Flywheel eccentric overload exercises versus barbell half squats for basketball players: Which is better for induction of post-activation performance enhancement?

Hezhi Xie; Wenfeng Zhang; Xing Chen; Jiaxin He; Junbing Lu; Yuhua Gao; Duanying Li; Guoxing Li; Hongshen Ji; Jian Sun

doi:10.1371/journal.pone.0277432

. 2022 Nov 21;17(11):e0277432. doi: 10.1371/journal.pone.0277432

Flywheel eccentric overload exercises versus barbell half squats for basketball players: Which is better for induction of post-activation performance enhancement?

Hezhi Xie ^1,^‡, Wenfeng Zhang ^2,^‡, Xing Chen ², Jiaxin He ², Junbing Lu ², Yuhua Gao ¹, Duanying Li ¹, Guoxing Li ¹, Hongshen Ji ¹, Jian Sun ^1,^*

Editor: Laurent Mourot³

PMCID: PMC9678314 PMID: 36409686

Abstract

Objective

This study compared the post-activation performance enhancement (PAPE) effects of a flywheel eccentric overload (FEOL) exercise and barbell half squats (BHS) on countermovement jump (CMJ) and 30 m sprint performance.

Methods

Twelve male collegiate competitive basketball players were enrolled in this study and they implemented two training protocols: barbell half squat (BHS) and flywheel eccentric overload (FEOL) training. The BHS protocol included three intensities of load: low (40% 1RM), medium (60% 1RM), and high (80% 1RM), with each intensity consisting of 5 sets of 3 repetitions. The FEOL protocol included three inertia intensities: low (0. 015 kg∙m²), medium (0.035 kg∙m²), and high (0.075 kg∙m²), with each intensity consisting of 3 sets of 6 repetitions. The measurement time points were before training (baseline) and at 3, 6, 9, and 12 minutes after training. A two-stage (stage-I and stage-II) randomized crossover design was used to determine the acute effects of both protocols on CMJ and sprint performance.

Results

At each training intensity, the jump height, jump peak power output (PPO), jump impulse and 30m sprint speed at 3, 6, 9, and 12 minutes after BHS and FEOL training did not change significantly compared to the baseline. A 2-way ANOVA analysis indicated significant main effects of rest intervals on jump height, jump PPO, and jump impulse, as well as 30m sprint speed. The interaction of the Time × protocol showed a significant effect on jump height between BHS and FEOL groups at high intensity in stage-I (F = 3.809, p = 0.016, df = 4) and stage-II (F = 3.044, p = 0.037, df = 4). And in high training intensity, the jump height at 3 (7.78 ± 9.90% increase, ES = 0.561), 6 (8.96 ± 12.15% increase, ES = 0.579), and 9 min (8.78 ± 11.23% increase, ES = 0.608) were enhanced in I-FEOL group compared with I-BHS group (F = 3.044, p = 0.037, df = 4). In stage-II, the impulse and sprint speed of the FEOL group were significantly higher than those of the BHS group at 6, 9, and 12 min under low (FEOL = 0.015kg∙m², BHS = 40%1RM), medium(FEOL = 0.035kg∙m², BHS = 60%1RM), and high (FEOL = 0.075kg∙m², BHS = 80%1RM) intensities. Furthermore, the sprint speed of the two training protocols did not change at different time points. The interaction of Time × training intensity showed lower sprint speeds in the II-BHS group at a high intensity (BHS = 80%1RM) compared to low (BHS = 40%1RM) and medium (BHS = 60%1RM) training intensities, especially at 9 min and 12 min rest intervals.

Conclusion

Although barbell half squat training and flywheel eccentric overload training did not provide a significant PAPE effect on explosive power (CMJ and sprint) in male basketball players, FEOL training showed a better potential effect on enhanced CMJ jump performance at the high training intensity.

Introduction

The characteristics of basketball require players’ high levels of neuromuscular abilities including power output, strength, and speed [1]. Both strength and power training programs for basketball players should focus on developing the performance of explosive movements [2]. An acute enhancement in explosive sport performance namely throws, sprints and jumps can be achieved due to the muscular phenomenon called post-activation potentiation (PAP) [3] and an alternative term has been proposed in 2017, a post-activation performance enhancement (PAPE) [4]. Despite both are helpful in the increment of sports performance, differences exist in underlying physiological mechanisms and in the time of enhancement persistence. The primary underlying PAP mechanism is the phosphorylation of the myosin regulatory light chain and a very short period (<3 min) [5–8], while PAPE would be associated with other potential mechanisms namely muscle temperature [9], water content [10] and a longer “window of opportunity” (>4 min) [4, 11] as well as the presence of possible neural mechanisms [12, 13]. In training practice, the potentiation can be achieved by the execution of biomechanically similar conditioning activity (CA) [14] at maximal or near-maximal intensities prior to the subsequent athletic task. As our further in-depth understanding of the physiological mechanism of acute effects in muscle contractile function, many studies have indicated that an appropriate induction protocol can successfully induce PAPE.

Squat exercises can induce PAPE in the lower limbs. Most representative studies have reported positive effects of weighted squat training on athletes’ performance in jump height, rate of force development, response time, maximal power, and maximal speed [15–18]. High and moderate weighted squats (90% and 60% of 1RM, respectively) have been reported to improve sprint and countermovement jump (CMJ) performance in male subjects [19, 20]. Additionally, flywheel ergometer squat training can also enhance the acute effects of strength, power, sprint, jumps, and maximal voluntary contraction [21–27]. These play an important role in most of the necessary movements in the sport.

Flywheel ergometer squat training stimulates eccentric overload training (EOL), where the eccentric muscle force generated (e.g., flexion phase of the squat) exceeds the maximum concentric force (e.g., extension phase of the squat) [28–30]. In conventional squat training, there is a short pause between the ECC and CON movements. In contrast, the movements in the flywheel squat pattern are coupled and involve a stretch-shortening cycle, which may facilitate CON muscle activation and strength building [31]. However, eccentric overload has been reported to appear to be a means of increasing eccentric power and rate of force development (RFD) rather than concentric output [32]. Currently, there is only 1 literature comparing the acute effects of PAPE on physical performance induced by conventional squats and flywheel ergometers respectively, and only one training intensity [33]. Therefore, there is a need for a longitudinal study of both training protocols (with multiple intensities).

Previous studies on the PAPE effect have mostly focused on explosive power-based sports such as throwing [34], weightlifting [35], soccer [36], rugby [15], and track and field [37]. The effects of PAPE activation induced by barbell squatting and EOL training in elite basketball players over a season are rarely reported. This study aimed to compare the influence of exercise modality (FEOL or BHS) and intensity (low (FEOL = 0.015kg∙m², BHS = 40%1RM), moderate (FEOL = 0.035kg∙m², BHS = 60%1RM), and high (FEOL = 0.075kg∙m², BHS = 80%1RM)) on PAPE in CMJ and sprint in basketball players.

Methods

Experimental approach to the problem

A two-phase randomized crossover study was used. Participants underwent a total of 12 training sessions lasting 13 weeks, with a washout period at week 7. The subjects had one additional familiarization session prior to the experiment. In stage-I (weeks 1–6), subjects were randomized into two groups (I-FEOL vs. I-BHS). In stage-II (weeks 8–13), the training modalities of the two groups of subjects were swapped, that is, I-FEOL was replaced by II-BHS, and I-BHS was replaced by II-FEOL. To compare the acute effects of the FEOL protocol and BHS protocol on CMJ and sprint performance after each training session (each intensity), the subjects underwent two rounds of either the FEOL protocol or the BHS protocol in each stage. The measurement time points for CMJ or sprint performance were set at baseline and at 3, 6, 9, and 12 minutes after each training session. We assumed that the low, medium or high resistance in the FEOL and BHS protocols were equivalent. The results are therefore inherently based on how well the intensities are matched. Each protocol contained three intensities: low (FEOL = 0.015kg∙m², BHS = 40%1RM), medium (FEOL = 0.035kg∙m², BHS = 60%1RM), and high (FEOL = 0.075kg∙m², BHS = 80%1RM), with one intensity implemented each week. First round (1–3 weeks) of stage-I included week 1 = low, week 2 = medium, week 3 = high, and jump performance was measured. Second round (weeks 4–6) of stage-I included week 4 = low, week 5 = medium, week 6 = high, and sprint performance was measured. Phase two crossover trials. Round one (8–10 weeks) of stage-II was week 8 = low, week 9 = medium, week 10 = high, and jump performance was measured. Second round (weeks 11–13) of stage-II was week 11 = low, week 12 = medium, week 13 = high, and sprint performance was measured (shown in Fig 1).

The authors interrupted one training session (week 7) as a washout period (14 days between training sessions) to mitigate the effects of the first program on the second one, which were considered that the duration of the washout period needed further discussion. Participants did not alternate between CMJ and sprint tests during the first 3 training sessions based on the hypothesis that cross-validation after one training session (particularly in the FEOL protocol) might induce some muscle impairments that could lead to biased maximal performance at CMJ or sprint.

Participants

Eighteen players (all team members) of the basketball team from Guangzhou Sport University, participating in the National University Basketball League (CUBA), volunteered to participate in this test. The inclusion criteria were as follows: the absence of any injury or disease [38] (Physical Activity Readiness Questionnaire), regular participation in basketball team training (4 training sessions of 120 min each per week), 3 basketball training sessions (Monday, Wednesday, and Saturday), 1 physical training session (Friday), more than 1 year of heavy strength resistance training experience, and assessed by 2 physical training specialists (mean experience of 12 years) for their fitness status. The players in this trial typically performed resistance training in the strength and conditioning laboratory once a week as a training task, and therefore had a priori knowledge of the training protocol and testing methods. All subjects were informed about the potential risks and benefits of the current procedures and signed an informed consent form. The players were also asked to maintain habitual exercise for 48 h before the trial and not to intake any stimulant substances or alcohol. Finally, twelve participants (age 20.63 ± 1.32 years, range 19–23 years; body mass 21.96 ± 1.36 kg; height 187.56 ± 5.55 cm) were included in the final analysis (Table 1). This study was approved by the Academic Ethics Committee of Guangzhou Sport University (2021LCLL-11). All procedures were conducted according to the Declaration of Helsinki for studies involving human participants.

Table 1. Basic information of the participates.

Metrics	I-BHS (n = 6)	I-FEOL (n = 6)	Total	P
Age (years)	20±1.41	21.25±1.26	20.63±1.32	0.235
Height (cm)	190.5±3.7	184.63±3.15	187.06±3.55	0.161
Body weight (kg)	78.4±4.14	66.73±2.26	72.56±6.51	0.003^**
Body Mass Index(kg/m²)	23.25±0.58	20.68±0.43	21.96±1.36	<0.001^**

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** Significantly different from two groups at p < 0.05.

Procedures

During the first visit to the laboratory on a Friday afternoon one week prior to the trial, the basic information of all players was recorded. Height were measured using JENIX, DS-103M (Korea). Body and weight composition was recorded by experienced investigators using the InBody 370 body composition analyzer (Korea). Subsequently, the 1RM of a weighted half squat (knee angle 90°) was measured for all subjects under the guidance of a physical training specialist [39]. They were then informed and familiarized with the FEOL and BHS protocols, the CMJ jump and the 30m sprint test. On each subsequent Friday from 15:00–17:00, participants returned and were instructed to perform standardized warm-up exercises, including joint mobility, dynamic stretching, mid-zone activation, and specific exercises (e.g., weighted half squat and sprint) before performing tests and training sessions [40]. All tests and training interventions were set up with an appropriate movement control mode. Technical feedback from the field was provided by experienced investigators. Tests and training sessions were repeated once the movements were performed incorrectly or not at maximum effort by the players.

Measure

Countermovement jump

Participants arrived at the lab and had a standardized warm-up followed by a 3-minute passive rest period. Subsequently, their CMJ performance was recorded twice (using participant rotation as the rest interval) and the better test was considered as the baseline for that training session. CMJ jump performance was measured again at 3, 6, 9, and 12 minutes after the participants performed one intensity of either FEOL or BHS protocol, respectively. Meanwhile, Participants used passive recovery between time points. SmartJump (Fusion Sport; Australia) was used to assess the CMJ performance of the players. CMJ jumps were performed using a uniform movement pattern: Maximal effort CMJs were performed using a self-selected depth and with hands-on-hips to prevent the influence of arm swing [41]. An investigator provided technical feedback to ensure that the jumps were performed correctly and encouraged all participants to make their best efforts in the test. The following variables were selected for data analysis: jump height (cm), jump peak power output (W), and jump impulse (Ns). Smart jump obtained the following formula by measuring the air time during the jump during the jump:

Jump height (cm) = (Flight time /1000)²*g*100/8, where the unit of flight time is (ms), gravity (g) = 9.81 m/s.

Jump PPO(W) = 60.7*jump height+45.3*mass-2055, the PPO is an estimate and not a measurement.

30m sprint test

Participants arrived at the laboratory and had a standardized warm-up followed by a 3-minute passive rest period. The performances of two rounds (with participant rotation as the rest interval) of 30m sprints of the participants were recorded and the better one was the baseline for the training session. Participants performed the FEOL or BHS protocol and 30m sprint performance was measured again at minutes 3, 6, 9, and 12, respectively. They were allowed to use a passive recovery mode between time points. The Brower timing system (TC-1H, USA) was placed at the starting line and the finish line of the 30 m sprint track, 1 m above the ground. Specific positions of the players were designated less than 0.5 m from the starting line with their feet apart in front of them (high starting position), arms at the side of the body, and hips and knees slightly flexed. On the GO signal, the participants were instructed to perform a sprint and the sprint time of 30 m (0.00s) was recorded.

PAPE inducing action

Flywheel eccentric overload (FEOL) exercise protocol

The FEOL protocol was accomplished by performing repetitive half squats using a flywheel ergometer (Exxentric AB, Sweden). The flywheel dynamometer includes 3 inertial moment intensities: low (inertia moment = 0. 015 kg∙m²), medium (inertia moment = 0.035 kg∙m²), and high (inertia moment 0.075 kg∙m²), and only one intensity is executed per training session, each intensity is performed for 3 sets × 6 reps with 2 min of passive recovery between each set [40]. Participants started in a half squat position and were asked to execute the concentric phase as quickly as possible and to control the braking phase until the knees were flexed to approximately 90 degrees. An investigator provided technical feedback on each repetition. Participants received strong standardized encouragement to perform each repetition to the maximum extent possible [40].

Loaded barbell half squats (BHS) protocol

The BHS protocol was completed by performing weighted half squats using a barbell squat rack (YANBO J009, China). The BHS protocol consisted of 3 intensities: 40%, 60%, and 80% of 1RM. Only one intensity was performed in each training session, performing 5 sets × 3 reps with a 2-minute rest interval between sets for passive recovery [42]. Depending on the participant’s height, an elastic band was attached to the barbell squat rack crossbar and used as a control brake for the eccentric phase of the squat until the knees were bent to approximately 90 degrees (hips touching the elastic band). Participants used a high bar position mode of half squat and were asked to descend slowly during the eccentric phase and finish as quickly as possible during the centripetal phase. Two investigators provided technical feedback for each repetition. Participants received strong standardized encouragement to perform each repetition to the maximum extent possible. All experimental measurements were conducted in the digitalized strength and conditioning laboratory of Guangdong Province, China.

Statistical analysis

Statistical analysis was performed on SPSS software (v24.0, Chicago, USA). Data are presented as mean ± SD. Within-session reliability of test measures computed using a single measures two-way random intraclass correlation coefficient (ICC (2,1)) with an absolute agreement, inclusive of 95% confidence interval (relative reliability) [43] and the coefficient of variation (CV) (absolute reliability) [44]. ICC values less than 0.5 are indicative of poor reliability, values between 0.5 and 0.75 indicate moderate reliability, values between 0.75 and 0.9 indicate good reliability and values greater than 0.90 indicate excellent reliability. A CV ≤10% was set as the criterion to declare a variable as reliable. Analysis of variance (ANOVA) was performed for each variable in order to evaluate the significant modification of each score. Univariate analysis was performed using the groups (FEOL vs. BHS) as the between factor of the analysis and using the stage-I and stage-II as the within factor of the analysis. Multivariate analysis of variance for repeated measures (RM-MANOVA), was used to evaluate significant differences between the two groups (FEOL vs. BHS, named protocol), among different time points (0, 3, 6, 9 and 12 min, named Time), and in the interaction, Protocol × Time. RM-MANOVA was also used to evaluate significant differences among the different training intensity (low, medium, and high intensity, named Training intensity), and in the interaction, Time × Training intensity. One-way repeated-measure ANOVA was used to assess the effects of the two protocols (I- or II-BHS vs. I- or II-FEOL) on CMJ and sprint performance. If a meaningful F value was found, a Bonferroni post hoc test could be applied for correction. Time × protocol interaction and Time × training intensity interaction effects were analyzed using Pillai’s trace multivariate criteria. Cohen’s formula was used for evaluating the effect size (ES) of all dependent variables, including rest duration, exercise protocols, and intensity [45]. The influence degree was calculated and interpreted as follows: trivial < 0.200, 0.2 ≤ small < 0.6, 0.6 ≤ moderate < 1.20, 1.20 ≤ large < 2.0, very large ≥2.000 [40]. The significance was set at p < 0.05, and confidence interval was set at 95%.

Results

Test reliability

Within-session reliability data are presented in Table 2, implying that all data reported moderate to high reliability, with the exception of the I-BHS group (ICC = 0.45) and the I-FEOL group (ICC = 0.37) for stage-I of the medium-intensity post-training sprint test, the I-FEOL group (ICC = 0.34) for the high-intensity post-training sprint test, and the II-FEOL group (ICC = 0.01) for stage-II of the high-intensity post-training sprint test.

Table 2. Mean test ± standard deviations (SD), test reliability.

Stage	Groups	Metrics	Intensities	M±SD	ICC (2,1)	CV
Stage	Groups	Metrics	Intensities	M±SD	(95%CI)	(%,95%CI)
Stage 1	I-BHS	CMJ	Low	50.62±1.19	0.88 (0.47–0.99)	2.35 (0.18–4.52)
Stage 1	I-FEOL	CMJ	Low	55.16±1.24	0.80 (0.44–0.98)	2.24 (0.17–4.31)
Stage 1	I-BHS	CMJ	Medium	52.28±0.92	0.89 (0.63–0.99)	1.76 (0.14–3.39)
Stage 1	I-FEOL	CMJ	Medium	55.45±1.89	0.74 (0.30–0.97)	3.40 (0.27–6.54)
Stage 1	I-BHS	CMJ	High	52.45±0.39	0.82 (0.48–0.99)	0.75 (0.06–1.44)
Stage 1	I-FEOL	CMJ	High	55.84±1.80	0.76 (0.33–0.98)	3.22 (0.25–6.19)
Stage 1	I-BHS	PPO	Low	4569.90±67.38	0.96 (0.80–1.00)	1.47 (0.12–2.83)
Stage 1	I-FEOL	PPO	Low	4317.15±75.07	0.76 (0.37–0.98)	1.74 (0.14–3.34)
Stage 1	I-BHS	PPO	Medium	4669.71±62.24	0.96 (0.81–1.00)	1.34 (0.10–2.58)
Stage 1	pre- FEOL	PPO	Medium	4311.66±95.30	0.68 (0.28–0.97)	2.21 (0.17–4.25)
Stage 1	I-BHS	PPO	High	4684.84±23.80	0.95 (0.84–1.00)	0.50 (0.04–0.98)
Stage 1	I-FEOL	PPO	High	4358.38±109.21	0.77 (0.34–0.98)	2.50 (0.20–4.81)
Stage 1	I-BHS	Ns	Low	246.93±3.39	0.97 (0.83–1.00)	1.37 (0.11–2.64)
Stage 1	I-FEOL	Ns	Low	219.42±2.48	0.81 (0.45–0.98)	1.13 (0.09–2.17)
Stage 1	I-BHS	Ns	Medium	251.36±2.48	0.98 (0.89–1.00)	1.00 (0.08–1.90)
Stage 1	I-FEOL	Ns	Medium	220.04±3.75	0.81 (0.40–0.98)	1.70 (0.13–3.28)
Stage 1	I-BHS	Ns	High	251.96±0.95	0.98 (0.92–1.00)	0.38 (0.03–0.73)
Stage 1	I-FEOL	Ns	High	221.42±4.31	0.76 (0.34–0.98)	1.94 (0.15–3.74)
Stage 1	I-BHS	Sprint	Low	4.20±0.06	0.62 (0.20–0.96)	0.15 (0.12–2.87)
Stage 1	I-FEOL	Sprint	Low	4.00±0.03	0.63 (0.22–0.96)	0.69 (0.05–1.33)
Stage 1	I-BHS	Sprint	Medium	4.15±0.04	0.45 (0.07–0.93)	1.07 (0.08–2.07)
Stage 1	I-FEOL	Sprint	Medium	4.00±0.04	0.37 (0.03–0.91)	0.91 (0.07–1.75)
Stage 1	I-BHS	Sprint	High	4.09±0.03	0.67 (0.27–0.97)	0.79 (0.06–1.51)
Stage 1	I-FEOL	Sprint	High	4.03±0.07	0.34 (0.02–0.90)	1.65 (0.13–3.17)
Stage 2	II-FEOL	CMJ	Low	52.44±1.35	0.90 (0.62–0.99)	2.58 (0.20–4.96)
Stage 2	II-BHS	CMJ	Low	54.29±0.95	0.54 (0.14–0.95)	1.75 (0.14–3.36)
Stage 2	II-FEOL	CMJ	Medium	54.30±1.44	0.86 (0.46–0.99)	2.64 (0.21–5.08)
Stage 2	II-BHS	CMJ	Medium	54.74±0.97	0.78 (0.37–0.98)	1.77 (0.14–3.41)
Stage 2	II-FEOL	CMJ	High	55.04±1.31	0.79 (0.32–0.98)	2.37 (0.19–4.56)
Stage 2	II-BHS	CMJ	High	55.00±0.57	0.87 (0.60–0.99)	1.03 (0.08–1.99)
Stage 2	II-FEOL	PPO	Low	4683.90±82.19	0.96 (0.81–1.00)	1.75 (0.14–3.37)
Stage 2	II-BHS	PPO	Low	4264.17±57.63	0.59 (0.18–0.96)	1.35 (0.11–2.60)
Stage 2	II-FEOL	PPO	Medium	4796.98±87.18	0.95 (0.74–1.00)	1.82 (0.14–3.49)
Stage 2	II-BHS	PPO	Medium	4350.42±47.76	0.53 (0.08–0.95)	1.10 (0.09–2.11)
Stage 2	II-FEOL	PPO	High	4842.18±79.29	0.94 (0.69–1.00)	1.64 (0.13–3.15)
Stage 2	II-BHS	PPO	High	4336.88±36.13	0.55 (0.09–0.95)	0.83(0.07–1.60)
Stage 2	II-FEOL	Ns	Low	252.01±3.27	0.97 (0.88–1.00)	1.30 (0.10–2.50)
Stage 2	II-BHS	Ns	Low	217.78±1.91	0.80 (0.45–0.98)	0.88 (0.07–1.68)
Stage 2	II-FEOL	Ns	Medium	256.43±3.42	0.97 (0.84–1.00)	1.33 (0.10–2.56)
Stage 2	II-BHS	Ns	Medium	222.81±4.26	0.53 (0.09–0.95)	1.91 (0.15–3.68)
Stage 2	II-FEOL	Ns	High	258.14±3.08	0.97 (0.83–1.00)	1.19 (0.09–2.29)
Stage 2	II-BHS	Ns	High	221.27±3.61	0.46 (0.03–0.94)	1.63 (0.13–3.14)
Stage 2	II-FEOL	Sprint	Low	4.21±0.06	0.86 (0.54–0.99)	1.53 (0.12–2.94)
Stage 2	II-BHS	Sprint	Low	4.01±0.03	0.77 (0.40–0.98)	0.83 (0.07–1.60)
Stage 2	II-FEOL	Sprint	Medium	4.10±0.06	0.66 (0.23–0.97)	1.54 (0.12–2.96)
Stage 2	II-BHS	Sprint	Medium	4.00±0.03	0.85 (0.51–0.99)	0.79 (0.06–1.52)
Stage 2	II-FEOL	Sprint	High	4.07±0.05	0.58 (0.16–0.95)	1.27 (0.10–2.45)
Stage 2	II-BHS	Sprint	High	3.96±0.05	0.01 (-0.07–0.55)	1.27 (0.10–2.45)

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ICC values > 0.9 = excellent, 0.75–0.9 = good, 0.5–0.75 = moderate, and < 0.5 = poor, in accordance with Koo and Li. CV values were considered acceptable if < 10%.

Jump height

In stage-I, jump heights did not change significantly at low(FEOL = 0.015kg∙m², BHS = 40%1RM), medium(FEOL = 0.035kg∙m², BHS = 60%1RM), and high(FEOL = 0.075kg∙m², BHS = 80%1RM) training intensities, and the effect size of improvement for all dependent variables was below 0.60 (Fig 2A). Simultaneously, the jump height of the I-BHS and I-FEOL groups did no difference exists at each training intensity (Fig 2B).

Repeated measures ANOVA was performed on jump heights at each interval in the I-BHS group and the I-FEOL group. A 2-way ANOVA showed a significant main effect of rest intervals on jump height at low (FEOL = 0.015kg∙m², BHS = 40%1RM), medium (FEOL = 0.035kg∙m², BHS = 60%1RM), and high(FEOL = 0.075kg∙m², BHS = 80%1RM) training intensities (p < 0.05). Mauchly’s spherical hypothesis test showed that the interaction of the effect of Time × protocol on jump height had no statistical significance (F_low = 1.917, p = 0.190, df = 4) at a low (FEOL = 0.015kg∙m², BHS = 40%1RM) training intensity. However, it had a significant effect on jump height at moderate(FEOL = 0.035kg∙m², BHS = 60%1RM) and high(FEOL = 0.075kg∙m², BHS = 80%1RM) training intensities (F_medium = 3.584, p = 0.020, df = 4; F_high = 3.809, p = 0.016, df = 4; Fig 2A). In medium (FEOL = 0.035kg∙m², BHS = 60%1RM) training intensity, the jump height at 3 (9.12 ± 15.84% increase, ES = 0.472), 6 (6.03 ± 12.97% increase, ES = 0.389), and 9 min (6.20 ± 10.07% increase, ES = 0.513) were increased in I-FEOL group compared with the I-BHS protocol. And in high (FEOL = 0.075kg∙m2, BHS = 80%1RM) training intensity, the jump height at 3 (7.78 ± 9.90% increase, ES = 0.561), 6 (8.96 ± 12.15% increase, ES = 0.579), and 9 min (8.78 ± 11.23% increase, ES = 0.608) were enhanced in I-FEOL group compared with I-BHS group (Fig 2A, F_high = 3.044, p = 0.037, df = 4). Furthermore, the interaction of Time × training barely affected jump height (p > 0.05, Fig 2B). Additionally, repeated-measures ANOVA was performed on the jump height at each rest interval at different intensities. None of the effects of the interaction of Time × training intensities on jump height had any statistical significance (p > 0.05, Fig 2B).

In stage-II, different intensities of BHS and FEOL training also did not affect the jump height (Fig 2A and 2B). Repeated measures ANOVA of jump height at each rest interval in the II-FEOL and II-BHS groups showed that the Time × protocol interaction did not affect jump height at low(FEOL = 0.015kg∙m², BHS = 40%1RM) and medium(FEOL = 0.035kg∙m², BHS = 60%1RM) training intensities (F_low = 1.689, p = 0.185, df = 4; F_medium = 0.923, p = 0.580, df = 4; Fig 2A). However, a significant interaction effect (Time × protocol) was observed at high training intensities (F_high = 3.044, p = 0.037, df = 4; Fig 2A). Furthermore, the interaction of Time × training barely affected jump height (p > 0.05, Fig 2B).

For participants who underwent FEOL training in stage-I, BHS training in stage-II did not affect the jump height among different intensities at 3 (ES = 0.084), 6 (ES = 0.243), 9 (ES = 0.202), and 12 (ES = 0.208) min (p > 0.05, Fig 2C). Similarly, for the participants who underwent BHS training in stage-I, FEOL training in stage-II did not affect the jump among different intensities at 3 (ES = 0.432), 6 (ES = 0.283), 9 (ES = 0.338), and 12 (ES = 0.314) min (p > 0.05, Fig 2C).

Jump peak power

In stage-I, there was no significant difference after BHS and FEOL training at the three training intensities, and the effect size of improvement for all dependent variables ranged from 0.072–0.455 (Fig 3A). Additionally, there was no significant difference in PPO between I-BHS and I-FEOL group at different measuring time points (Fig 3A). Furthermore, there was no significant difference in PPO between I-BHS and I-FEOL group at each training intensity (Fig 3A).

The 2-way ANOVA showed a significant main effect of rest interval on PPO (p < 0.05). At high(FEOL = 0.075kg∙m², BHS = 80%1RM) training intensity, the interaction of Time × protocol had a significant improving effect on PPO (F_high = 3.809, p = 0.016, df = 4; Fig 3A). However, the interaction of Time × training at intensity also did not affect PPO (p > 0.05, Fig 3B).

In stage-II, different intensities of BHS and FEOL training did not affect PPO (Fig 3A and 3B). Furthermore, there was no significant change in PPO at the levels of Time × protocol interaction and Time × training intensity interaction (p > 0.05, Fig 3A and 3B).

For participants who underwent FEOL training in stage-I, BHS training in stage-II nearly did not affect PPO (p > 0.05, Fig 3C). Additionally, for the participants who underwent BHS training in stage-I, FEOL training in stage-II did not affect the PPO at each time point (p > 0.05, Fig 3C).

Jump impulse

In stage-I, the jump impulse after BHS and FEOL training was almost unchanged compared with the baseline value (Fig 4A). However, the impulse in the I-BHS group was significantly higher than that in the I-FEOL group at 9 min, and 12 min at low (FEOL = 0.015kg∙m², BHS = 40%1RM), medium (FEOL = 0.035kg∙m², BHS = 60%1RM), and high (EFOL = 0.075kg∙m², BHS = 80%1RM) intensities (p < 0.05; Fig 4A). At medium (FEOL = 0.035kg∙m², BHS = 60%1RM) and high (FEOL = 0.075kg∙m², BHS = 80%1RM) training intensities, the Time × protocol interaction affected the impulse (Fig 4A). Compared to the I-FEOL protocol, the impulse in I-BHS group was markedly higher at medium (F_medium = 3.775, p = 0.016, df = 4) and high training intensities (F_high = 3.042, p = 0.037, df = 4).

In stage-II, the impulse of the II-FEOL group was significantly higher than that of the II-BHS group in 6 min, 9 min, and 12 min at low (FEOL = 0.015kg∙m², BHS = 40%1RM), medium (FEOL = 0.035kg∙m², BHS = 60%1RM), and high (EOL = 0.075kg∙m², BHS = 80%1RM) intensities (p < 0.05; Fig 4A). Neither the Time × protocol interaction term nor Time × training intensity showed an effect on impulse (Fig 4A and 4B).

For participants who performed FEOL training in stage-I, there was no significant difference in the impulse between both stages after receiving BHS training in stage-II (p > 0.05, Fig 4C). Similarly, for participants who performed BHS training in stage-I, there was no significant difference in the impulse between the two stages after receiving FEOL training in stage-II (p > 0.05, Fig 4C).

Sprint speed

In stage-I, the sprint speed after BHS and FEOL training almost had no significant change compared to the baseline value (p > 0.05, Fig 4A). The sprint speed of the I-FEOL group was significantly lower than that of the I-BHS group at 9 min of low (3.81 ± 1.26% decrease, p = 0.009, ES = 0.843; Fig 5A) and medium (2.74 ± 1.64% decrease, p = 0.029, ES = 0.759; Fig 5A) intensity. The Time × protocol interaction and the Time × training intensity interaction barely affected the sprint speed (p > 0.05, Fig 5A and 5B).

In stage-II, there was no significant difference in sprint speed between the II-FEOL group and the II-BHS group at each rest interval at low (FEOL = 0.015kg∙m², BHS = 40%1RM) and medium (FEOL = 0.035kg∙m², BHS = 60%1RM) training intensities. However, at high (FEOL = 0.075kg∙m², BHS = 80%1RM) training intensity, the sprint speed of the II-FEOL group was significantly higher than that of the II-BHS group at 6 min (2.81 ± 1.17% increase, p = 0.042, ES = 0.73), 9 min (2.55 ± 0.38% increase, p = 0.032, ES = 0.75), and 12 min (3.16 ± 1.29% increase, p = 0.019, ES = 0.791) (Fig 5A). Although there was no significant difference in sprint speed between the II-FEOL and II-BHS groups at the level of Time × protocol interaction, there was a significant difference in sprint speed between the II-BHS and II-FEOL groups at the level of Time × training intensity (F = 2.500, p = 0.029; Fig 5B).

For participants who underwent FEOL training in stage-I, BHS training in stage-II had no effect on sprint speed (p > 0.05, Fig 5C). Similarly, for participants who underwent BHS training in stage-I, FEOL training in stage-II did not affect sprint speed (p > 0.05, Fig 5C).

Discussion

The main finding of this study was that no difference exists on CMJ and 30m sprint PAPE were induced by BHS and FEOL training after a two-phase crossover trial. However, jump height at rest intervals of 3 (7.78 ± 9.90% increase, ES = 0.561), 6 (8.96 ± 12.15% increase, ES = 0.579), and 9 (8.78 ± 11.23% increase, ES = 0.608), were greater for FEOL than BHS protocol.

A 13-week half squat training program was conducted along well as the standardization of training frequency, time, sets, repetitions, and rest intervals, to ensure comparability of training conditions between the two groups in both phases. Under such a circumstance, it is necessary and challenging to control for these variables when comparing the results of different training programs [46]. Therefore, a randomized crossover design was adopted in our study. A crossover design has an advantage of requiring a small sample size and eliminating difference between individuals [47]. In our crossover design, athletes underwent a 2-week washout period between stage-I and stage-II, which was essential for adjusting the heterogeneity across the athletes enrolled in this study. Although they did not perform resistance training during this period, whether the effects of this specific training impact stage-II needs to be further explored.

Flywheel resistance training used in this study is indeed really different from the plyometric mode of muscle action and therefore relies not on the same mechanical (e.g. paralelle or serie elastic component) and neural elements (e.g. stretch reflex). The rotational inertia during flywheel exercise causes a greater eccentric overload than that produced by the traditional resistance exercise [22]. The barbell training under different intensities was constant resistance training. Flywheel, by contrast, provided unlimited resistance under every intensity and presented maximum or closely-maximum activation from the beginning due to its inertia force. The characteristics of flywheel inertia are that as the inertia increases, the velocity of peak concentric, peak eccentric, average concentric, and average eccentric tends to decrease, whereas the ratio of peak eccentric and peak concentric power increases [30]. However, we found that there was no difference exists in jump height between the BHS and FEOL groups at different intensities within each time interval. Such variations might be explained by the actual program used for PAPE-induction, as mentioned previously.

In addition, FEOL training presented to be jump height-increasable, compared with BHS. Comparing II-BHS with II-FEOL, FEOL was more effective in increasing jump height, especially at 3 min, 6 min, and 9 min after training. Likewise, comparing I-BHS with I-FEOL, the latter was more effective at 3 min, 6 min, 9 min, and 12 min after training [26]. Previous studies demonstrated that a longer recovery interval (4 to 8 min) resulted in a better PAPE effect, compared with a shorter recovery time (2 to 3 min), though individual variations were observed therein [48]. Additionally, it was reported that the afferent excitability caused by muscle contraction could last for 3 to 10 min after exercise [49], which was consistent with our findings.

Both BHS training and FEOL training could not improve the performance of 30-meter sprint possibly due to different moving patterns of half-squat (BHS and FEOL) and sprint. However, the effect of preload stimulation on sprint performance was ambiguous. Some studies reported improvements [18, 50–52], some showed no change [19, 35, 36], and several proposed different results depending on testing distance [16] and timing of measuring [50]. This study found that the BHS group had lower sprint speed under high-intensity (BHS = 80%1RM) sessions, especially at intervals of 9 min and 12 min, compared with low (BHS = 40%1RM) and moderate (BHS = 60%1RM) intensities (F = 2.500, p = 0.029; Fig 5B). This difference might be associated with the distance (30 compared to the previous 5 and 10 meters) and measuring time.

There are still some limitations in this study. We assumed that the low, medium and high resistance were equivalent in the FEOL and BHS protocols. The results are therefore inherently based on how well the intensities are matched. However, due to the difference in the working patterns of the barbell and flywheel, the resistance is actually different at equal intensities. The effect of the PAPE method and recovery time on the PAPE enhancement effect was analyzed using repeated measurement, but the influence of muscle strength on the effect of PAPE was not investigated. Furthermore, in light of the parameters of this study, neither BHS nor FEOL could significantly increase the jump height of basketball players, whereas jumping ability is the basic athletic quality required by many events [37, 42]. Whether this is related to training volume, training intensity, muscle fiber type, or other factors remains to be investigated. Furthermore, we took into account the greater risk of 30-m maximal sprint-induced muscle damage. However, the repeated bout effect associated with eccentric strength training influenced the magnitude and etiology of the experimental training’s residual effects. Therefore, it was conceivable that the PAPE effects observed for sprint performance after 3 days of training did not represent the effects that could be observed after the first occurrence of eccentric strength training. In addition, gender factor must be considered in the practical application of PAPE [53]. Rixon et al. [54] enrolled 30 participants to perform maximal isometric squat protocol (maximal voluntary contraction PAPE) and maximal dynamic squat (DS) protocol (DS-PAPE) to induce PAPE, and the results showed that male participants were significantly better than females in both jump height and power output. Tsolakis et al. [53] conducted a study on 23 participants and showed that after inducing PAPE by isometric (3 sets of 3 sec) or plyometric (3 sets of 5 repetitions) bench and leg press, male participants outperformed female participants in both CMJ and bench press throw. As this study only analyzed the sports performance of male basketball players, we still need to expand the sample size and take gender into account in future research.

In summary, although barbell (BHS) and flywheel (FEOL) half squat training did not provide a significant PAPE effect on explosive power (CMJ and sprint) in male basketball players, FEOL training showed a better potential effect on enhanced CMJ jump performance following high-intensity (EOL = 0.075kg∙m²) training.

Practical applications

Jumping performance is important for basketball players. However, as mentioned previously, the effect of PAPE is only transitory and could not be effective during an entire match. Furthermore, players run from the onset of the match which can therefore offset the effectiveness of a conditioning protocol on jumping performance. Therefore, the limit related to the activity would instead stand upon the practicability of this protocol. PAPE protocols induced by half squats (barbell or flywheel) should be implemented in training to improve jumping performance during exercise and thus improve training effectiveness.

Supporting information

S1 Data

(XLSX)

Click here for additional data file.^{(996.7KB, xlsx)}

Acknowledgments

The authors thank the participants for their participation in this study.

Data Availability

All relevant data are within the manuscript and its Supporting Information files.

Funding Statement

The authors received no specific funding for this work.

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PLoS One. doi: 10.1371/journal.pone.0277432.r001

Decision Letter 0

Laurent Mourot

25 Mar 2022

PONE-D-22-02783Eccentric overload exercises versus loaded half squats for basketball players: which is better for induction of postactivation potentiation?PLOS ONE

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: General comment

The study aimed to test the influence of exercise modality (eccentric overloading or squatting) and intensity (light, moderate and heavy) on post-activation performance enhancement (and not PAP) in CMJ and sprint. The experimental protocol contain several bias that should be taken into account to appropriately discuss the findings. First, the authors implemented a cross-over designed for the conditioning exercise, but not for the load, which lead therefore to a progressive increase in load for all subjects. It would have therefore been more suitable to randomize the allocation order for load in order to avoid any adaptive effects from the load on the PAPE response. Then, the intensity and volume of the two conditioning protocols differed which could results into different workload between the two protocol. In absence of quantification of the total workload during exercise, it is difficult to account for this effect on the PAPE effect. Finally, this study thought to improve recommendation about conditioning protocol to improve jump performance in basketball players. However, the context of these recommendations should be precise in the context of this activity; that is, whether such protocol should be implemented at the onset of a match (but with likely confounding effects from sprint actions performed), or during training to optimize training effectiveness.

Furthermore, due to the multiple conditions (allocation group, exercise and intensity), the protocol and the results section are difficult to understand, and needs to be thoroughly amend or rephrase to improve this particularly limiting point. Many sentences are therefore confusing and scramble understanding of the results.

Finally, some elements are lacking to support statement provided particularly in the discussion section. Authors should therefore strengthen their rational in order to avoid sections that only describe findings of the present or previous studies, but provide more elements to understand the present findings and conclude on recommendations.

Please find below specific comments :

1. L 52: Undefined previously, please define

2. L 54-55: "Could increase PPO to a certain extent" is an inapropriate statement to present results. Please rephrase or present the magnitude of this increase.

3. L 58: performances were only assessed at different precise timing after exercise, and not during different period after exercise termination. Therefore, I suggest using time-points rather than time windows.

4. L 67-70: Please conform to the findings of the cited reference (and others e.g.; Blazevich and Babault, 2019; DOI: 10.3389/FPHYS.2019.01359), by mentioning the difference between electrically-evoked and voluntary improvements in performance. With reference to the area of interest of the present study, authors monitored PAPE and not PAP

5. L 72-74: Only referring to phosphorylation of MHC or change in fascicle pennation angle is really scarce in light of others potentials factors driving improvement in voluntary performance (e.g. muscle temperature, muscle blood flow), and particularly when focusing on eccentric mode of muscle action (e.g. neural factors). Please amend to provide a reliable overview of these mechanisms.

6. L 78: typing error : provided

7. L 80-81: Because squat exercise modality can induce a PAPE only in the lower limbs (in comparison to the upper limbs), I suggest the authors to precise this element in order to avoid misunderstanding by novice readers.

8. L 82-83: Please precise which parameters were improved in these studies (e.g. jump height, rate of force development, reaction time, maximal power, maximal speed, ...). Indeed, the conflicting findings about the factors improved by PAPE which depend upon the conditioning sequence should be avoid here.

9. L 85: "Has been pro" should be rephrase for a better understanding

10. L 96-100: Please also report the above-mentioned study (i.e. Norrbrand 2010) that reported similar improvement in MVC than the concentric training. A more reliable overview of the litterature, and the conflicting conclusions, should be drawn here.

11. L 101-103: Although scarce, please cite some references focusing on jumping performance (e.g. French et al., 2003, DOI: 10.1519/ 1533-4287(2003)017<0678:CIDEPF>2.0.CO;2)

12. L 116: It is unclear what are the short-term effects mentioned here. The authors stated a two-stages randomized cross-over study, lasting for 13 weeks. Therefore, are the short-term effects the acute effects following bouts of exercise, or the immediate effects of the training protocol tested at the end of the last bout? Should be precise.

13. L 116: The greater sprint performance could only be speculated here, and could therefore be mentioned as an expected finding at the end of the introduction section. I suggest the authors to rephrase this sentence in order to differentiate between the expected, and the actual findings of the protocol.

14. L 129: Rephrase as : and they were then informed about the EOL protocol.

15. L 130-131: Please provide additional explanations about the expected effects of the familiarization procedure for experienced subjects.

16. L 133-139: The procedure implemented to assess CMJ and sprint performance requires further supporting elements. Could the authors indicate for instance why they did not alternate the testing between CMJ and sprint? It could be suppose that the first 3 bouts of exercse (and particularly during the EOL protocol) induced some muscular impairments leading to bias the maximal performance during CMJ or sprint. Could the authors provide reliability measurements between sessions to account for this possible confounding factor?

17. L 139: Please add the time-delay allowed between the two sequences of this protocol.

18. Also, justify that the 1-week washout period is sufficient to alleviate the effects of the first protocol on the testing and effectiveness of the second sequence. (which seems unlikely).

19. L 149: I recommend the authors to avoid the excessive use of decimals and report the appropriate precision provided by the measurements they performed. For instance, rouding age to the nearest year as they ask to the participants, or report body-mass to the precision allowed by the body scale.

20. L 161: Should be : "subjects were asked to"

21. L 170: Please detail what are those "basic information"

22. L 178-180: Do the authors control for the reproducibility between the two trials to ensure the validity of the calculated mean? If so, please provide the accepted range between trials to ensure two maximal performance.

23. L 181: What was the recovery modality allowed to the subjects between the different time points?

24. L 191-193: Please provide the height of the photoelectric cells.

25. L 205: In accordance with one of my previous comment regarding the lack of details about the "basic information" recorded by means of body scale, the authors should provide additional information regarding the method used to calculate body surface area.

26. L 207-209: Please precise whether the pace was controlled during the downward phase of the half squat. If so, this information should be added to provide an estimate of the braking resistance applied by the subjects

27. L 214-215: It seems that the amount of repetitions per set is lacking here. Please amend.

28. L 225-227: Provide further explanations about the meaning one his one-way ANOVA. Indeed, your protocol implemented wo exercises and three modality. How could the authors therefore performed only a one-way ANOVA?

29. L 233-234: Statistical information are lacking in figures (significant different and not only ANOVA F or p values) forcing the readers to back-and-forth between figures and text. It could be therefore suitable to add the calculated 95%CI on the graphs and symbols to indicate statistical differences.

30. L 240-243: The comparisons between time points and intensity for pre-HS and pre-EOL is unclear here. It is state in the protocol that each session differed from the other by the testing protocol (HS or EOL) or the intensity (low, med and high). Please amend therefore to understand which variables were compared here.

31. L 249: Could you please indicate the degree of freedom for the F value of the ANOVA. In addition, I suggest to avoid the appelation of week1, 2 or 3, should rather precise the intensity that is one of the main independent variable.

32. L 252-253: This sentence requires rephrasing to avoid misinterpretation. Under the current version, this sentence would means that the performance at PRE is significantly related to measurements made at POST. However, it seems that this analysis was not performed, and is not of primary importance for this study.

33. L 263-265: It could be suitable to report the magnitude of the significant changes in the text to allow the reader a better adoption of the findings.

34. L 277-278: This third comparison lacks of support here, and should be presented in the statistics section.

35. L 282-283: This sentence is misconducting here since the mention of rest interval suggest that post-measurements would be presented, while it seems that comparison is performed on PRE measurements. Please amend and/ or correct.

36. L 284-285: Please state clearly this difference in the text

37. L 288-290: Again this sentence is misconducting, since is could be understand that the PRE-HS value is significantly correlated to PPO. Please rephrase.

38. L 333-335: How could the authors state that the sprint speed of PRE-EOL could be lower than PRE-HS at 9-min rest interval? Once again this sentence is conflicting here and needs to be rephrase.

39. L 342-344: Interactions rather revealed significant differences than influenced results. Please rephrase for a better understanding.

40. L 361-362: It would be suitable to differentiate between stretch shortening cycle occurring during running or CMJ for instance and the succession of eccentric and concentric phase with no (or only a few) storage of passive elastic energy (e.g. squatting). Flywheel resistance training used in the present study is indeed really different from plyometric mode of muscle action, and relies therefore not on the same mechanical (e.g. paralelle or serie elastic component) and neural elements (e.g. stretch reflex). Please amend and rephrase.

41. L 369-370: This aim differ from the scientific question addressed in the introduction section, and is therefore not supported by the rational. Please ensure consistency about the objectives of this study throughout the manuscript.

42. L 398-404: There are contradictory findings mentioned here between improvement in CMJ height and PPO due to EOL training, while non-statistical difference is noted. Please based your statement on the statistical findings and not graphical reading.

43. L 428-430: This section is quite descriptive and lacks of elements to explain the absence of significant improvement in this study. The authors should strenghten their discussion and provide scientific elements explaining their findings. Such approach would benefits to coaches in order to better understand how they could improve their intervention.

44. L438-440: I acknowledge that jumping performance is important for basketball players. However, as it is mentioned previously, the effect of PAPE is only transitory and would not be effective during an entire match. Furthermore, players runs from the onset of the match that can therefore offset the effectiveness of a conditioning protocol on jumping performance. Therefore the limit related to the activity would rather stands upon the practicability of this protocol. Authors should therefore provide recommendations or perspectives about how to applied such protocol for performance improvement. That is, should a PAPE protocol should be implement before a match (with a relatively low efficiency given the other actions, see above), or to used during training session in order to improve performance during exercise in order to improve training effectiveness?

45. L 447-449: This sentence contradicts the first one of the conclusion section. Please ensure coherence about the presence or absence of PAPE phenomenom in the present study. This question remains unclear while reading this section.

46. L 449-452: Both squatting and flywheel are based on eccentric-concentric contractions here. It appear therefore obvious to precise more specifically the different exercise modalities (e.g.; phase duratin, intensity, ...).

Reviewer #2: Abstract

• Line 46-47: not clear, rephrase and explain clearly the design.

• Lines 49-51: not useful in an abstract.

• Lines 52-58: there is no consistency between the methods and the results. The dependent parameters were not listed, nor the extent of the changes was reported. Please rewrite this section in accordance with what reported in the methods

• The last sentence makes no sense since every movement is a combination of concentric/eccentric actions.

Introduction

• Lines 103-106: It is not clear what “long season” means here. Please explain.

• Overall, why half-squat and not other squat variations? Please elaborate.

Methods

• Line 195: PAP or PAPE?

• The statistical analysis should be rerun: it is not clear to me why two different two-way analysis were performed instead of a three-way.

This is a major point that should be addressed. Therefore, I have stopped my review here, since the results should be rewritten accordingly.

Reviewer #3: General comments:

This study compared the post-activation performance enhancement induced by two forms of resistance exercise (flywheel and barbell half squats) and the effects of such training protocols over a period of weeks. The authors should be congratulated for performing a cross-over multiple week investigation. The study, and particularly the longitudinal nature, are a useful addition to the literature. However, there are a number of issues that I wish to raise. The most significant of these is the fact that it is not clear exactly what statistical analyses have been performed due to some confusion in the wording. Many assumptions or justifications inherent in the analyses are also missing. These factors make it difficult to follow and assess aspects of the Results and Discussion. I have mentioned some other specific comments, too.

Comment 1: The manuscript refers to post-activation potentiation (PAP) throughout – attributed to phosphorylation of myosin regulatory light chains. However, this ignores the recent body of literature questioning these mechanisms and time-courses and suggesting that post-activation performance enhancement would be a more appropriate name. Please see https://doi.org/10.3389/fphys.2019.01359 and related literature for example. The Introduction as a whole is quite short and missing some key literature.

Comment 2: The terms used to describe the exercises are quite vague. For example, an eccentric overload could be achieved in many different ways and a ‘loaded half squat’ could also be achieved in different ways. In fact, it could be argued that both exercises are ‘loaded half squats’.

Comment 3: The loads used for the barbell squat are individual-specific (a percentage of 1RM) but the flywheel inertias are not. This warrants further consideration or discussion.

Comment 4: In the statistical analysis section, it is stated that one-way repeated measures ANOVAs were performed. However, a few lines later on talk about interaction effects, which suggest that at least a two-way ANOVA was performed. It is therefore unclear what statistical analyses were performed – how many ANOVAs, what factors, and what conditions or intensities are in each. It is also mostly unclear whether the two phases are being tested separately or with all data combined (and why). The inherent assumptions in your statistical model also need to be considered and discussed. For example, are you assuming that the two lowest intensities (flywheel and barbell) are equivalent and the two highest are equivalent, etc.? Should you control for baseline values and/or session number or any other variables? You should also report confidence intervals (e.g. https://doi.org/10.1080/14763141.2020.1782555 ). Other recommendations in that editorial such as reporting exact p-values should also be followed. These factors make it difficult to follow and assess aspects of the Results and Discussion. Perhaps the Discussion would be easier to follow if it followed the narrative of the tests – i.e. one ANOVA at a time and discussing the main and interaction effects / post-hocs clearly.

Specific comments:

Authors: It is not clear how there can be three co-first authors.

Short title: Compared to what?

Data availability statement: I suggest that you upload the data alongside the manuscript for readers and reviewers in line with journal policy.

Abstract:

Line 52: PPO should be defined. Peak power output? It would also be useful to include some statistical results within the abstract.

Introduction:

Lines 74-75: This statement is too dramatic/ambitious and should be reduced in everity.

Line 95: Other studies have investigated the relationship between flywheel moment of inertia and velocity or power (concentric and eccentric) during flywheel half squats – see https://doi.org/10.1080/02640414.2020.1860472 This is also important on line 217 where the statement about ‘different components of muscle power’ is quite vague and could be supported more.

Lines 101-106: Although not on jumping sports, quite a few PAPE studies have focused on vertical or horizontal jumps. These have investigated the effect of factors such as the flywheel inertia, number of sets, etc. on flywheel PAPE. For some examples:

https://doi.org/10.1123/ijspp.2019-0476 (review paper)

https://doi.org/10.1519/JSC.0000000000003214 (effect of inertia)

https://doi.org/10.1123/ijspp.2019-0411 (effect of volume)

https://doi.org/10.3390/sports9010005 (effect of inertia and jump direction on ground reaction force parameters)

Methods:

Lines 118-120: It’s unclear how many sessions this is in total. How many familiarisation sessions were performed if any? See https://doi.org/10.1123/ijspp.2017-0282 but be aware of the use of magnitude based inference (e.g. https://doi.org/10.1080/14763141.2020.1782555 )

Line 148: Why 12 participants? This number should be justified. See https://doi.org/10.1525/collabra.33267

Line 161 and elsewhere: I suggest being consistent with ‘participants’ or ‘subjects’ – the section is called ‘Participants’ so it would be good to stick with this.

Lines 178 and 188: Why were two trials averaged? Why two and why an average?

Lines 185-186: How were these parameters calculated? There are multiple possible methods for some of them.

Line 192: What was the starting position for the sprint? In line with the timing gate or slightly behind?

Line 201: Why 3 sets x 6 reps? The volume PAPE paper mentioned earlier could be used here, but it is important to justify these choices.

Lines 208-209: Were participants instructed to resist throughout the eccentric phase or only in a certain portion of it?

Lines 232-233: These should be reworded with signs such as ‘greater than or equal to’ to ensure that there are no gaps. For example, 1.195 and 1.995 currently have no category.

Results:

I suggest adding tables to make the results clearer.

Discussion:

Line 368: ‘shown’ may be better than ‘proved’ – to show more uncertainty.

It would be good to re-summarise the main overall results early in the Discussion.

Lines 369-370: More justification is needed for why basketballers might be different to other populations and why results might not continue over a season.

Line 382: What is meant by ‘ground-lifting’?

Lines 384-387: Some of the studies I mentioned above (e.g. the effects of inertia on PAPE) may be useful here. Likewise, for lines 390-391 where the differential effects of peak power / velocity / force are discussed.

Line 397: Could this be controlled for within the statistical analysis?

Line 411: Was this ‘tendency’ significant? If not then it should not be discussed as an effect. The same applies in line 448 (if not then this should not be part of the conclusion).

Lines 418/420/421 – consistency needed around minutes / -minutes / min

**********

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PLoS One. 2022 Nov 21;17(11):e0277432. doi: 10.1371/journal.pone.0277432.r002

Author response to Decision Letter 0

25 May 2022

Dear editor and reviewers

Regarding the manuscript ID (NO.PONE-D-22-02783) entitled " Eccentric overload exercises versus loaded half squats for basketball players: which is better for induction of postactivation potentiation?". Thank you for your letter and the reviewers' comments on our manuscript entitled " Eccentric overload exercises versus loaded half squats for basketball players: which is better for induction of postactivation potentiation?" (NO.PONE-D-22-02783) were evaluated. These comments were valuable and helpful to us in revising and improving the paper, as well as important guidance for our research. We have carefully studied these comments and made revisions, which we hope will be approved by all of you. The revised parts are marked in red in the thesis.and The main corrections in the paper and the responses to the reviewers are listed below.

Responds to Reviewer #1:

1. Response to comment: L 52:Undefined previously, please define.

Responds: We greatly appreciate the reviewers' comments. We have changed the definition of PPO to Peak power output (PPO). In L52

2. Response to comment: L 54-55:"Could increase PPO to a certain extent" is an inapropriate statement to present results. Please rephrase or present the magnitude of this increase.

Responds: Thank you for your valuable comments. For the reviewers' valuable comments, we have revised the content to EOL training in the second stage increased PPO to a certain extent, especially at 3 min (p=0.046, ES=0.716). In L56-58

3. Response to comment: L 58:Performances were only assessed at different precise timing after exercise, and not during different period after exercise termination. Therefore, I suggest using time-points rather than time windows.

Responds: Thank you for your valuable comments. For the valuable comments of the reviewers. We have changed the time windows to time-points. In L63-64

4. Response to comment: L 67-70:Please conform to the findings of the cited reference (and others e.g.; Blazevich and Babault, 2019; DOI: 10.3389/FPHYS.2019.01359), by mentioning the difference between electrically-evoked and voluntary improvements in performance.

Responds: We are very grateful for the reviewers' comments. For the reviewers' valuable comments, we add the study by Blazevich and Babault. In this study, the term PAPE was used in relation to the enhancement of muscle contraction after conditioning activity. In L80-81

5. Response to comment: L 72-74:Only referring to phosphorylation of MHC or change in fascicle pennation angle is really scarce in light of others potentials factors driving improvement in voluntary performance (e.g. muscle temperature, muscle blood flow), and particularly when focusing on eccentric mode of muscle action (e.g. neural factors). Please amend to provide a reliable overview of these mechanisms.

Responds: We are very grateful for the reviewers' comments. After carefully reading the reviewers' comments, we have added the concepts and mechanisms related to PAP and PAPE. In L83-90.

6. Response to comment: L 78:Typing error : provided

Responds: Thank you for your valuable comments. After carefully reading the reviewers' comments, we have changed the typing to provided.

7. Response to comment: L 80-81:Because squat exercise modality can induce a PAPE only in the lower limbs (in comparison to the upper limbs), I suggest the authors to precise this element in order to avoid misunderstanding by novice readers.

Responds: We greatly appreciate the reviewers' comments. For the reviewer's valuable comment, we have changed it to Squat exercise can induce a PAPE in the lower limbs. In L94.

8. Response to comment: L 82-83:Please precise which parameters were improved in these studies (e.g. jump height, rate of force development, reaction time, maximal power, maximal speed, ...). Indeed, the conflicting findings about the factors improved by PAPE which depend upon the conditioning sequence should be avoid here.

Responds: Thank you for your valuable comments. After carefully reading the reviewers' comments, we have listed the relevant metrics: strength, power, sprint, jumps and maximal voluntary contraction (MVC). In L100.

9. Response to comment: L 85:"Has been pro" should be rephrase for a better understanding

Responds: Thank you for your valuable input. After carefully reading the article, we have changed to Heavy and moderate weighted squats (90% and 60% of 1RM, respectively) have been reported to improve sprint and CMJ performance in male subjects. In L97

10. Response to comment:. L 96-100:Please also report the above-mentioned study (i.e. Norrbrand 2010) that reported similar improvement in MVC than the concentric training.

Responds: Thank you for your valuable input. After carefully reading the article, we have made revision and addition in the corresponding places.

11. Response to comment: L 101-103:Although scarce, please cite some references focusing on jumping performance (e.g. French et al., 2003, DOI: 10.1519/ 1533-4287(2003)017<0678:CIDEPF>2.0.CO;2)

Responds: Thank you for your valuable comments. After carefully reading the reviewers' comments, we have described their impact on jump performance and added relevant references. In L114-116.

12.Response to comment: L 116:It is unclear what are the short-term effects mentioned here. The authors stated a two-stages randomized cross-over study, lasting for 13 weeks.

Responds: We are very grateful for the reviewers' comments. We have rewritten the sentences to compare the acute effects of the EOL protocol (three intensities) and the HS protocol (three intensities) on CMJ jump height or 30 m sprint performance after each training session(each intensity). In L129-131

13.Response to comment: L 116:The greater sprint performance could only be speculated here, and could therefore be mentioned as an expected finding at the end of the introduction section.

Responds: We are very grateful to the reviewers for giving such a high rating to our article. We have rewritten the Experimental approach to the problem in order to be more clear about the design of the experiment and in response to the question you raised. In L124-140

14.Response to comment: L 129:Rephrase as : and they were then informed about the EOL protocol.

Responds: After reading the article carefully, we have rewritten the sentence: They were then informed and familiarized with the EOL and HS protocols, CMJ jumps and 30m sprint tests. In L173-175.

15.Response to comment: L 130-131:Please provide additional explanations about the expected effects of the familiarization procedure for experienced subjects.

Responds: Thank you for your valuable suggestions. After carefully reading the reviewers' comments, we have added the following clarification: Participants in this trial typically performed resistance training in the strength and conditioning laboratory once a week as a training task, and therefore had a priori knowledge of the training protocol and testing methods. An additional familiarization exercise was provided prior to the experiment. In L158-160.

16.Response to comment: L 133-139:The procedure implemented to assess CMJ and sprint performance requires further supporting elements. Could the authors indicate for instance why they did not alternate the testing between CMJ and sprint?

Responds: We are grateful to the reviewers for their comments. We are currently hypothesizing in accordance with your opinion that participants did not alternate CMJ and sprint tests during the first 3 sessions based on the hypothesis that cross-testing after one training session (particularly in the EOL protocol) may induce some muscle damage that could lead to biased maximal performance at CMJ or sprint. We also tried to further improve the reliability of our conclusions by conducting the same repeated trials based on the same group of investigators at different time periods. In L144-147.

17.Response to comment:. L 139:Please add the time-delay allowed between the two sequences of this protocol.

Responds: We are very grateful for the reviewers' comments. We would like to express the meaning: Training break of 1 week (14 days) between the two programs. In L141-144.

18.Response to comment:Also, justify that the 1-week washout period is sufficient to alleviate the effects of the first protocol on the testing and effectiveness of the second sequence. (which seems unlikely).

Responds: We greatly appreciate the reviewers' comments. We are currently revising in accordance with your comments to: The authors interrupted the training sessions for 1 week as a washout period (14 days between training sessions) to mitigate the effects of the first protocol on the second protocol tested further research was required. In L141-144.

19.Response to comment:L 149:I recommend the authors to avoid the excessive use of decimals and report the appropriate precision provided by the measurements they performed.

Responds: We greatly appreciate the reviewers' comments. We have added the table about the basic information of the participates. (age, height, weight, etc.) to the attachment. L 260-265

20.Response to comment:L 161:Should be : "subjects were asked to"

Responds: Thank you for your valuable comments. We have revised the presentation. All subjects were informed about the potential risks and benefits of the current procedures and were asked to signed an informed consent form. In L162.

21.Response to comment:L 170:Please detail what are those "basic information"

Responds: We are very grateful for the reviewers' comments. We have added the table about the basic information of the participates. (age, height, weight, etc.) to the attachment. L 260-265

22.Response to comment:. L 178-180:Do the authors control for the reproducibility between the two trials to ensure the validity of the calculated mean? If so, please provide the accepted range between trials to ensure two maximal performance.

Responds: We greatly appreciate the reviewers' comments. We have added the motion control method between the two trials: All test and training interventions are set up with the appropriate movement control mode. Technical feedback from the field is provided by experienced investigators. Tests and training sessions are re-executed once the subject's movements are incorrectly executed or not at maximum effort. In L178-182.

23.Response to comment:L 181: What was the recovery modality allowed to the subjects between the different time points?

Responds: We are grateful for the reviewers' comments. We added the recovery method for different time points and the participants used passive recovery between time points. In L191-192.

24.Response to comment: L 191-193:Please provide the height of the photoelectric cells.

Responds: We greatly appreciate the reviewers' comments. We have added the height of the equipment: These photocells were mounted 1 m above floor level. In L207.

25.Response to comment:L 205:In accordance with one of my previous comment regarding the lack of details about the "basic information" recorded by means of body scale, the authors should provide additional information regarding the method used to calculate body surface area.

Responds: Thank you for your valuable comments. We appreciate the reviewers' comments. We have added the basic information to the attachment. We are very sorry that our Inbody370 device was not able to provide body scale calculations.

26.Response to comment: L 207-209:Please precise whether the pace was controlled during the downward phase of the half squat. If so, this information should be added to provide an estimate of the braking resistance applied by the subjects.

Responds: Thank you for your valuable comments. We have added the motion control method. Subjects started in a half-squat position and were asked to execute the concentric phase as quickly as possible and to control the braking phase until the knees were flexed to approximately 90 degrees. In L219-222.

27.Response to comment: L 214-215:It seems that the amount of repetitions per set is lacking here. Please amend.

Responds: Thank you for your valuable comments. We have modified the number of reps. For performing 5 sets × 3 reps with a 2-minute rest period between sets. In L229.

28.Response to comment: L 225-227:Provide further explanations about the meaning one his one-way ANOVA. Indeed, your protocol implemented two exercises and three modality. How could the authors therefore performed only a one-way ANOVA?

Responds: We apologize for any confusion caused in the article. In our design, different intensity(3 intensities) was implemented each week for three weeks, and repeated measures of outcome indicators were performed after each trial. Given the specificity of the trial, we viewed the three intensities as independent of each other and therefore performed a one-way repeated measures ANOVA in each intensity. We also did a two-way ANOVA. We have uploaded the statistics in the attachment and hope it will help you to solve the confusion of reading. L 241-256

29.Response to comment: L 233-234:Statistical information are lacking in figures (significant different and not only ANOVA F or p values) forcing the readers to back-and-forth between figures and text. It could be therefore suitable to add the calculated 95%CI on the graphs and symbols to indicate statistical differences.

Responds: Thank you for your valuable comments that would enhance the quality of our manuscript. We have tried as much as we can, however, due to the dense graphics, the graphics appear more confusing after adding 95% CI, which seriously affects the clarity of the graphics. For this reason, we weighed again and again and apologized for not adding 95% CI to the graphics. We have uploaded the statistics in the attachment and hope it will help you to solve the confusion of reading.

30.Response to comment: L 240-243:The comparisons between time points and intensity for pre-HS and pre-EOL is unclear here. It is state in the protocol that each session differed from the other by the testing protocol (HS or EOL) or the intensity (low, med and high). Please amend therefore to understand which variables were compared here.

Responds: Thank you for your valuable comments that so enhance the quality of our manuscript, and We have revised the study design of the manuscript, which we hope will contribute to the understanding of the results. In the first phase (weeks 1-6) participants were randomized into two groups (pre-EOL vs. pre-HS) and in the second phase (weeks 8-13) participants crossed over between the two groups (pre-EOL to post-HS, pre-HS to post-EOL). We also have revised flowchart of the experiment. and re-uploaded it as an attachment. In L126-129

31.Response to comment: L 249: Could you please indicate the degree of freedom for the F value of the ANOVA. In addition, I suggest to avoid the appelation of week1, 2 or 3, should rather precise the intensity that is one of the main independent variable.

Responds: Thank you for your valuable comments that so enhance the quality of our manuscript, and We have made revisions and added information to the manuscript in the appropriate places based on the comments.

32.Response to comment: L 252-253:This sentence requires rephrasing to avoid misinterpretation. Under the current version, this sentence would means that the performance at PRE is significantly related to measurements made at POST. However, it seems that this analysis was not performed, and is not of primary importance for this study.

Responds: We apologize for any confusion caused in the article. We used a two-stage crossover design. We have revised the study design of the manuscript, which we hope will contribute to the understanding of the results. In the first phase (weeks 1-6) participants were randomized into two groups (pre-EOL vs. pre-HS) and in the second phase (weeks 8-13) participants crossed over between the two groups (pre-EOL to post-HS, pre-HS to post-EOL). We also have revised flowchart of the experiment. and re-uploaded it as an attachment.

33.Response to comment: L 263-265:It could be suitable to report the magnitude of the significant changes in the text to allow the reader a better adoption of the findings.

Responds: Thank you for your valuable comments that so enhance the quality of our manuscript, and We have revised the sloppy presentation. We have add the magnitude of the significant changes in the text, and uploaded the statistics in the attachment and hope it will help you to solve the confusion of reading. L 299

34.Response to comment: L 277-278:This third comparison lacks of support here, and should be presented in the statistics section.

Responds: Thank you for your valuable comments that so enhance the quality of our manuscript, and We have made additional revision in the statistics section. In L248

35.Response to comment:: L 282-283:This sentence is misconducting here since the mention of rest interval suggest that post-measurements would be presented, while it seems that comparison is performed on PRE measurements. Please amend and/ or correct.

Responds: We apologize for any confusion caused in the article. Thank you for your valuable comments that so enhance the quality of our manuscript, and We have modified the experimental design. Since the previous presentation of the experimental design caused confusion in your reading of the results. Again, we apologize. In L124-140

36.Response to comment: L 284-285:Please state clearly this difference in the text

Responds: Thank you for your valuable comments that so enhance the quality of our manuscript, and we have completed the changes in the manuscript. We have added relevant information. In L321-323

37.Response to comment:L 288-290:Again this sentence is misconducting, since is could be understand that the PRE-HS value is significantly correlated to PPO. Please rephrase.

38.Response to comment: L 333-335:How could the authors state that the sprint speed of PRE-EOL could be lower than PRE-HS at 9-min rest interval? Once again this sentence is conflicting here and needs to be rephrase.

39.Response to comment:L 342-344: Interactions rather revealed significant differences than influenced results. Please rephrase for a better understanding.

Responds: Thank you for your valuable comments. We have revised the inappropriate statement. Change affect to influence. L380-381

40.Response to comment: L 361-362:It would be suitable to differentiate between stretch shortening cycle occurring during running or CMJ for instance and the succession of eccentric and concentric phase with no (or only a few) storage of passive elastic energy (e.g. squatting).

Responds: We are very grateful for the reviewers' comments. We have added your summary. In L411-413

41.Response to comment:L 369-370:This aim differ from the scientific question addressed in the introduction section, and is therefore not supported by the rational. Please ensure consistency about the objectives of this study throughout the manuscript.

Responds: We are very grateful for the reviewers' comments. We have removed the inappropriate expressions. And revised the presentation in the introduction and the discussion section so that the discussion is consistent with the introduction.

42.Response to comment:L 398-404:There are contradictory findings mentioned here between improvement in CMJ height and PPO due to EOL training, while non-statistical difference is noted. Please based your statement on the statistical findings and not graphical reading.

Responds: We apologize for any confusion caused in the article. Thank you for your valuable comments that so enhance the quality of our manuscript, and we have revised the presentation in the introduction and the discussion section and modified the experimental design. Since the previous presentation of the experimental design caused confusion in your reading of the results. we have re-uploaded the flowchart of the experiment and the statistical results. Again, we apologize. In L124-140

43.Response to comment:L 428-430:This section is quite descriptive and lacks of elements to explain the absence of significant improvement in this study.

Responds: We are very grateful for the reviewers' comments. We have revised the inappropriate statement. In L430-438

44.Response to comment:L 438-440:I acknowledge that jumping performance is important for basketball players. However, as it is mentioned previously, the effect of PAPE is only transitory and would not be effective during an entire match.

Responds: We are very grateful for the reviewers' comments. We have revised the description and added a Practical Application section. In L470-477

45.Response to comment: L 447-449:This sentence contradicts the first one of the conclusion section. Please ensure coherence about the presence or absence of PAPE phenomenom in the present study. This question remains unclear while reading this section.

Responds: We are very grateful for the reviewers' comments. We have rewritten the conclusion. In L465-468. We apologize for any confusion caused in the article. Thank you for your valuable comments that so enhance the quality of our manuscript, and We have modified the experimental design. Since the previous presentation of the experimental design caused confusion in your reading of the results. we have re-uploaded the flowchart of the experiment and the statistical results. Again, we apologize. In L124-140

46.Response to comment: L 449-452:Both squatting and flywheel are based on eccentric-concentric contractions here. It appear therefore obvious to precise more specifically the different exercise modalities (e.g.; phase duratin, intensity, ...).

Response to Reviewer #2:

1.Response to comment: Line 46-47:Not clear, rephrase and explain clearly the design.

Responds: We apologize for any confusion caused in the article. Thank you for your valuable comments that so enhance the quality of our manuscript, and We have modified the Methods L 42-51. We have modified the experimental design. Since the previous presentation of the experimental design caused confusion in your reading of the results. we have re-uploaded the flowchart of the experiment and the statistical results. Again, we apologize. In L124-140

2.Response to comment: Lines 49-51: Not useful in an abstract.

Responds: Thank you for your valuable input. We have removed the inappropriate statement.

3.Response to comment: Lines 52-58:There is no consistency between the methods and the results.

Responds:We apologize for any confusion caused in the article. Thank you for your valuable comments that so enhance the quality of our manuscript, and We have modified the result. L52-66 We have modified the experimental design. Since the previous presentation of the experimental design caused confusion in your reading of the results. we have re-uploaded the flowchart of the experiment and the statistical results. Again, we apologize. In L124-140

4.Response to comment: The last sentence makes no sense since every movement is a combination of concentric/eccentric actions.

Responds: Thank you for your valuable input. We have removed the inappropriate statement.

5.Response to comment: Lines 103-106:It is not clear what “long season” means here. Please explain.

Responds: We are very sorry that our presentation has caused you confusion. We intended to say over a season. In L117

6.Response to comment:Overall, why half-squat and not other squat variations? Please elaborate.

Responds: We are very sorry that our presentation has caused you confusion. We have modified the expression, the flywheel exercise is a half-squat movement pattern, in order to compare the effect of the two programs, the traditional squat also uses the barbell half-squat pattern.

7.Response to comment:: Line 195:PAP or PAPE?

8.Response to comment:The statistical analysis should be rerun: it is not clear to me why two different two-way analysis were performed instead of a three-way.

Responds: Thank you for such valuable comments, and we have asked several statistical experts to conduct a thorough evaluation of the statistical methods in the manuscript, and they believe that we have a cross-sectional design, however a repeated measures design nested within it that measures outcome indicators at different time points, so the two-factor ANOVA and single-cause repeated measures ANOVA used in the current manuscript support our conclusions well.

9.Response to comment:: This is a major point that should be addressed. Therefore, I have stopped my review here, since the results should be rewritten accordingly.

Responds: For this, I am very sorry. We have made many revision changes to address the issues you have raised. Please continue to review our manuscript. Thank you.

Response to Reviewer #3:

1.Response to comment: The manuscript refers to post-activation potentiation (PAP) throughout – attributed to phosphorylation of myosin regulatory light chains.

Responds: We are very grateful for the reviewers' comments. After carefully reading the reviewers' comments, We adopted the concept of PAPE, complemented the relevant literature, and described the mechanisms associated with PAP and PAPE. In L83-90.

2.Response to comment: The terms used to describe the exercises are quite vague. For example, an eccentric overload could be achieved in many different ways and a ‘loaded half squat’ could also be achieved in different ways. In fact, it could be argued that both exercises are ‘loaded half squats.

Responds: We are very grateful for the reviewers' comments. We have carefully reviewed and rewritten the methods. We compare flywheel eccentric overloading and barbell squatting.

3.Response to comment: The loads used for the barbell squat are individual-specific (a percentage of 1RM) but the flywheel inertias are not. This warrants further consideration or discussion.

Responds: We are very grateful for the reviewers' comments. We acknowledge that comparing the effects of two different movement patterns is a great challenge, and we have discussed it. In L402-410

4.Response to comment: In the statistical analysis section, it is stated that one-way repeated measures ANOVAs were performed. However, a few lines later on talk about interaction effects, which suggest that at least a two-way ANOVA was performed. Responds: Thanks to such valuable comments, we have rephrased the study design and uploaded the study roadmap with the results of data analysis. We have also considered carefully and invited statistical experts for a thorough review of the study methodology in the manuscript. However, they felt that they believed that we were a cross-sectional design and, with a repeated measures design nested within it that measured outcome indicators at different time points, and therefore, suggested that a two-factor ANOVA and a single-cause repeated measures ANOVA would support our conclusions well in the manuscript.

Although we did not make the assumption that the two minimum strengths (flywheel and barbell) are equal, we standardized the movement pattern of the half squat (flywheel and barbell) and We used the lightest weight and inertia torque of the two devices as the low intensity for this test. We also consider this a great challenge.

5.Response to comment: Specific comments:Authors: It is not clear how there can be three co-first authors.

Responds: We have revised to two co-first authors.

6.Response to comment: Short title: Compared to what?

Responds: We are very grateful for the reviewers' comments. Flywheel half-squat compare to barbell half-squat exercise.

7.Response to comment: Data availability statement: I suggest that you upload the data alongside the manuscript for readers and reviewers in line with journal policy.

Responds: We are very grateful for the reviewers' comments. We have uploaded the statistics rusult in the attachment.

8.Response to comment: Line 52:PPO should be defined. Peak power output? It would also be useful to include some statistical results within the abstract.

Responds: We greatly appreciate the reviewers' comments. We have changed the definition of PPO to Peak power output (PPO). In L52

9. Response to comment: Lines 74-75:This statement is too dramatic/ambitious and should be reduced in everity.

Responds: We greatly appreciate the reviewers' comments. We have modified the inappropriate statement. In L80-93

10. Response to comment:Line 95:Other studies have investigated the relationship between flywheel moment of inertia and velocity or power (concentric and eccentric) during flywheel half squats – see https://doi.org/10.1080/02640414.2020.1860472

Responds: We greatly appreciate the reviewers' comments. We have added and revised the presentation in the preface and discussion sections, and added references.

11. Response to comment: Lines 101-106:Although not on jumping sports, quite a few PAPE studies have focused on vertical or horizontal jumps.

Responds: We are very grateful for the reviewers' comments. As the presentation has been rewritten, we have added relevant references in different places.

12. Response to comment: Lines 118-120:It’s unclear how many sessions this is in total. How many familiarisation sessions were performed if any?

Responds: We are very grateful for the reviewers' comments. 12 sessions in total, an additional 1 familiarization sessions were performed, and we have cited references and modified the presentation accordingly. The corresponding statement was modified in the method section. We have modified the experimental design. Since the previous presentation of the experimental design caused confusion in your reading of the results. we have re-uploaded the flowchart of the experiment and the statistical results. Again, we apologize. In L124-140

13. Response to comment: Line 148:Why 12 participants? This number should be justified. See https://doi.org/10.1525/collabra.33267

Responds: Thank you for your valuable comments that so enhance the quality of our manuscript, and we have the changes in the manuscript. The entire membership of a basketball team participated in the trial, originally 18, with 6 withdrawing due to injury. In L260-265

14. Response to comment:Line 161 and elsewhere:I suggest being consistent with ‘participants’ or ‘subjects’ – the section is called ‘Participants’ so it would be good to stick with this.

Responds: Modified to: participants.

15. Response to comment: Lines 178 and 188:Why were two trials averaged? Why two and why an average?

Responds: We are very grateful for the reviewers' comments. We have revised the presentation. Two tests were conducted to ensure that it was a maximum effort and that the results met the criteria of the movement pattern. The best performance was used for statistical analysis. In L188 and L202

16. Response to comment: Lines 185-186:How were these parameters calculated? There are multiple possible methods for some of them.

Responds: Thank you for your valuable comments. The jump performance parameters were measured by Smart Jump (Fusion Sport; Australia) and standardized to the CMJ movement pattern. In L193-195

17. Response to comment: Line 192:What was the starting position for the sprint? In line with the timing gate or slightly behind?

Responds: We are very grateful for the reviewers' comments. We have revised the presentation. In L207-209

18. Response to comment:Line 201:Why 3 sets x 6 reps? The volume PAPE paper mentioned earlier could be used here, but it is important to justify these choices.

Responds: Thank you for your valuable comments that so enhance the quality of our manuscript. The exercise was performed by reference: 10.1519/JSC.0000000000003005. The applicability of the method will be studied in depth subsequently. Maroto-Izquierdo et al. (10.5114/biolsport.2020.96318) found that a single set (i.e., 6 repetitions) of the half-squat flywheel exercise performed with the optimal concentric peak power intensity in physically active young men led to significant acute gains in CMJ jump height.

19 Response to comment:Lines 208-209: Were participants instructed to resist throughout the eccentric phase or only in a certain portion of it?

Responds: Thank you for your valuable comments that so enhance the quality of our manuscript, and we have revised in the manuscript. Eccentric process is resisted, knee flexion control at 90 degrees as the limit for centripetal contraction. In L219-224

20. Response to comment:Lines 232-233:These should be reworded with signs such as ‘greater than or equal to’ to ensure that there are no gaps. For example, 1.195 and 1.995 currently have no category.

Responds: Thank you for your valuable comments. We have rephrased trivial (<0.200), small (0.200 - 0.599), moderate (0.600 - 1.199) and large (1.200 -1.999), very large (≥2.000). In L254-255

21. Response to comment:I suggest adding tables to make the results clearer.

Responds: Thank you for your valuable comments. We have added the statistical result in the attachment.

22. Response to comment:Line 368:‘shown’ may be better than ‘proved’ – to show more uncertainty.

Responds: Thank you for your valuable comments. We have revised the inappropriate statement.

23. Response to comment: It would be good to re-summarise the main overall results early in the Discussion.

Responds: Thank you for your valuable comments. We have rewritten the main overall results early in the Discussion. In L397-401

24. Response to comment:Lines 369-370: More justification is needed for why basketballers might be different to other populations and why results might not continue over a season.

Responds: Thank you for your valuable comments. We have added Practical Applications. In L 470-477

25. Response to comment: Line 382:What is meant by ‘ground-lifting’?

Responds: Thank you for your valuable comments. Due to inaccurate translation, we have removed the expression.

26. Response to comment: Lines 384-387:Some of the studies I mentioned above (e.g. the effects of inertia on PAPE) may be useful here. Likewise, for lines 390-391 where the differential effects of peak power / velocity / force are discussed.

Responds: Thank you for your valuable comments. We have revised the presentation and cited the relevant literature. In L 418-423

27. Response to comment: Line 397: Could this be controlled for within the statistical analysis?

Responds: Thank you for your valuable comments. We did make relevant controls, re-upload the study roadmap and data statistics, and rewrote the study design to make it easier to understand.

28. Response to comment:Line 411:Was this ‘tendency’ significant? If not then it should not be discussed as an effect. The same applies in line 448 (if not then this should not be part of the conclusion).

Responds: Thank you for your valuable comments. We have revised the word to effect in the relevant position.

29. Response to comment: Lines 418/420/421-consistency needed around minutes / -minutes / min

Responds: Thank you for your valuable input. For consistency of presentation, we have modified the expression to read: min.

We gratefully appreciate for your valuable suggestion

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And all the changes are marked in red in revised paper.

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.

Once again, thank you very much for your comments and suggestions.

Yours sincerely,

Jian Sun, School of Athletic Training, Guangzhou Sport University, Guangzhou, P.R. China, E-mail: sunjian@gzsport.edu.cn . Tel:+8613728059899

Attachment

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PLoS One. doi: 10.1371/journal.pone.0277432.r003

Decision Letter 1

Laurent Mourot

20 Jul 2022

PONE-D-22-02783R1Flywheel eccentric overload exercises versus barbell half squats for basketball players: which is better for induction of post-activation potentiation enhancement?PLOS ONE

Dear Dr. Sun,

Please submit your revised manuscript by Sep 03 2022 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

We look forward to receiving your revised manuscript.

Kind regards,

Laurent Mourot

Section Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #3: (No Response)

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2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #3: Partly

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #3: No

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4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

Reviewer #3: No

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #3: Yes

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6. Review Comments to the Author

Reviewer #1: I thank the authors for considering my comments that enable significant improvements in the manuscript. It remains however some misunderstandings from my first revision that should be corrected before publication. Please find below these elements :

Abstract

L 58-59, 60: My previous comment about the magnitude of PPO increase considered the value of the increase (in % pre for instance) rather than the effect size of the statistical analysis. This would better inform the readers about the main findings of this study in the abstract.

L 145-148: I understand the statement of the authors considering the greater risk to induce muscle impairments with a 30-m maximal sprint. However, the repeated bout effect associated to eccentric strength training impact the magnitude and etiology of the experimental training’s residual effects. Therefore, it is conceivable that the PAPE effects observed for sprint performance after 3 days of training will not represent the effects that would be observed after the first occurrence to eccentric strength training. I suggest the authors to add this limit in the present article.

L 171: “basic information” is useless and could be remove to avoid excessive wordings (e.g. “participants’ height, age, weigth,…” is satisfactory).

Results:

L296-299: it seems that my comment in R1 was not well understood by the authors, which contribute also to confusion in the abstract. By “amplitude” I would say, could the authors provide the percentage increase (or decrease) in participants’ performance? The effect size refers to the power of the statistical analysis, but that is of moderate importance for practical application of the protocol from coaches and strength conditioners. Please add here, and in the abstract, the % change from PRE for your values.

L 380-381: again my comment in revision #1 was not understand. The statistical results of the ANOVA describe the differences observed in your study. This analysis (and the interaction provided here) made a posteriori could not “affect” or “influence” the sprint speed. The results of the ANOVA showed differences between the post-EOL and post-HS groups. Please correct carefully.

Reviewer #3: General comments:

I previously stated that, among other issues, it was unclear what statistical analyses had been performed. The previously recommended revisions have mostly been addressed/clarified, although a few areas remain difficult to interpret.

Comment 1: I still do not believe it is appropriate to consider low/medium/high intensity as being equivalent between the two exercises. For example, what rationale is there to assume that 40% and 0.015 are both low and that 80% and 0.075 are both high.? It is also worth noting that 80% is double 40% but 0.075 is five times 0.015. This may affect the statistical analysis used, but if not then it should at least be discussed as an assumption upon which the results rest.

Comment 2: In the statistical analysis section, it is much improved but still could be clearer exactly what variables are being assessed in what combinations/conditions. I suggest taking more words to spell this out in great detail. For example, the one-way ANOVA on line 247-248 can’t be the 2x2 pre/post HS/EOL and also can’t be the 2x1 pre/post or HS/EOL, so it’s not clear where the one-way ANOVA comes from. Generally, the statistics are easier to follow in the Results section because each individual result is discussed one at a time.

Comment 3: Despite changing to ‘barbell half squat’ and ‘flywheel eccentric overload’, the abbreviations HS and EOL are used. As previously stated, both are half squats and there are many ways of eliciting an eccentric overload. I suggest simply using the terms ‘barbell’ and ‘flywheel’ or including B and F in the abbreviations if necessary.

Comment 4: I also suggest avoiding the terms pre and post as they do not refer to the pre and post PAPE effect, which is confusing.

Comment 5: When referring to peak power or impulse, in many cases it is not stated whether this is during a jump or a sprint. This should always be clear in case a reader only reads specific sections.

Specific comments:

Title: This should be ‘performance’, nit ‘potentiation’ for PAPE

Lines 23-24: The authors should be commended for making the statistical results available in full, although this should not be stated as making the underlying data available.

Line 59: The ‘stages’ have not been explained yet so this is hard for someone to follow if only reading the abstract. These stages are called phases elsewhere, so it should be consistent.

Line 198: What method is used to calculate these? I know it is from Smart Jump, but readers should be told what method is used for the calculations.

Lines 254-255: There are still gaps – e.g. 0.5995. I suggest e.g. 0.2 ≤ small < 0.6; 0.6 ≤ moderate < 1.2.

Lines 260-265: this information should be in the participants section of the Methods.

Line 267: No criteria were given in the Methods for determining moderate or excellent reliability.

Line 276: Please do not say ;tended to increase’ if it was not significant.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #3: No

**********

PLoS One. 2022 Nov 21;17(11):e0277432. doi: 10.1371/journal.pone.0277432.r004

Author response to Decision Letter 1

21 Aug 2022

Question#1: Abstract: L 58-59, 60: My previous comment about the magnitude of PPO increase considered the value of the increase (in % pre for instance) rather than the effect size of the statistical analysis. This would better inform the readers about the main findings of this study in the abstract.

Response: Thank you very much for your suggestion. We have replaced effect size with percentages. Please see L58-59 and L61.

Question#2: L 145-148: I understand the statement of the authors considering the greater risk to induce muscle impairments with a 30-m maximal sprint. However, the repeated bout effect associated to eccentric strength training impact the magnitude and etiology of the experimental training’s residual effects. Therefore, it is conceivable that the PAPE effects observed for sprint performance after 3 days of training will not represent the effects that would be observed after the first occurrence to eccentric strength training. I suggest the authors to add this limit in the present article.

Responds: Thank you very much for your suggestion. We have added the relevant content. Please see L482-487.

Question#3: L 171: “basic information” is useless and could be remove to avoid excessive wordings (e.g. “participants’ height, age, weigth,…” is satisfactory).

Responds: Thank you very much for your suggestion. We have removed this section.

Question#4: Results: L296-299: it seems that my comment in R1 was not well understood by the authors, which contribute also to confusion in the abstract. By “amplitude” I would say, could the authors provide the percentage increase (or decrease) in participants’ performance? The effect size refers to the power of the statistical analysis, but that is of moderate importance for practical application of the protocol from coaches and strength conditioners. Please add here, and in the abstract, the % change from PRE for your values.

Responds: Thank you very much for your suggestion. We have added the corresponding percentages. Please see L322-323, L360, L395, L401-402, L408.

Question#5: L 380-381: again my comment in revision #1 was not understand. The statistical results of the ANOVA describe the differences observed in your study. This analysis (and the interaction provided here) made a posteriori could not “affect” or “influence” the sprint speed. The results of the ANOVA showed differences between the post-EOL and post-HS groups. Please correct carefully.

Responds: Thank you very much for your suggestion. We have corrected the relevant content. Please see L354-356, L403-406.

Reply to the third reviewer as follows:

Question#6: I still do not believe it is appropriate to consider low/medium/high intensity as being equivalent between the two exercises. For example, what rationale is there to assume that 40% and 0.015 are both low and that 80% and 0.075 are both high.? It is also worth noting that 80% is double 40% but 0.075 is five times 0.015. This may affect the statistical analysis used, but if not then it should at least be discussed as an assumption upon which the results rest.

Response: Thank you for your suggestion. We're not looking at low/medium/high intensity as an equivalence between the two sports. The low, medium, and high intensity of both types of exercise are relative terms. For the choice of training intensity in BHS, we refer to the study of Buscà et al. [1]. For the choice of training intensity in FEOL, we refer to the study of Petersen et al. [2].

[1] B. Buscà, J. Aguilera-Castells, J. Arboix-Alió, A. Miró, A. Fort-Vanmeerhaeghe, J. Peña, Influence of the Amount of Instability on the Leg Muscle Activity During a Loaded Free Barbell Half-Squat, International journal of environmental research and public health, 17 (2020).

[2] J. Petersen, K. Thorborg, M.B. Nielsen, E. Budtz-Jørgensen, P. Hölmich, Preventive effect of eccentric training on acute hamstring injuries in men's soccer: a cluster-randomized controlled trial, The American journal of sports medicine, 39 (2011) 2296-2303.

Question#7: In the statistical analysis section, it is much improved but still could be clearer exactly what variables are being assessed in what combinations/conditions. I suggest taking more words to spell this out in great detail. For example, the one-way ANOVA on line 247-248 can’t be the 2x2 pre/post HS/EOL and also can’t be the 2x1 pre/post or HS/EOL, so it’s not clear where the one-way ANOVA comes from. Generally, the statistics are easier to follow in the Results section because each individual result is discussed one at a time.

Response: Thank you for your suggestion. The main method of our study was a crossover design, however, to observe time effects, we further added a repeated measures design. Finally, to analyze the intervention mode and time effects, we used a combination of one-way ANOVA and repeated measures ANOVA. We have supplemented the relevant statement in the Methods section. Please see L266-275.

Question#8: Despite changing to ‘barbell half squat’ and ‘flywheel eccentric overload’, the abbreviations HS and EOL are used. As previously stated, both are half squats and there are many ways of eliciting an eccentric overload. I suggest simply using the terms ‘barbell’ and ‘flywheel’ or including B and F in the abbreviations if necessary.

Responds: Thank you for your suggestion. We have made changes to the relevant content. Please see Revised Manuscript and Revised Figures.

Question#9: I also suggest avoiding the terms pre and post as they do not refer to the pre and post PAPE effect, which is confusing.

Responds: We are sorry for our inappropriate presentation. We have replaced "pre" and "post" with "I" and "II", which represent the two training stages, Stage I and Stage II, respectively. We have modified the relevant content in the text and figures. Please see Revised Manuscript and Revised Figures.

Question#10: When referring to peak power or impulse, in many cases it is not stated whether this is during a jump or a sprint. This should always be clear in case a reader only reads specific sections.

Responds: We greatly appreciate the reviewer's comments. For the reviewer's valuable comments, we have stated in the text that it is peak power or impulse during the jump. Please see L207, L339, L368.

Question#11: Title: This should be ‘performance’, nit ‘potentiation’ for PAPE.

Responds: We are sorry for our carelessness. We have changed "potentiation" to "performance". Please see the Title and L72.

Question#12: Lines 23-24: The authors should be commended for making the statistical results available in full, although this should not be stated as making the underlying data available.

Responds: We have made changes to the Data Availability Statement. Please see L24.

Question#13: Line 59: The ‘stages’ have not been explained yet so this is hard for someone to follow if only reading the abstract. These stages are called phases elsewhere, so it should be consistent.

Responds: We are sorry for our inappropriate presentation. We have supplemented the relevant explanation of "stages" in the Abstract. In addition, we also corrected the incomprehensible “Phases” in the main text to the corresponding “stages-I” and “stage-II”. Please see L60, and Revised Manuscript.

Question#14: Line 198: What method is used to calculate these? I know it is from Smart Jump, but readers should be told what method is used for the calculations.

Responds: Your comments are greatly appreciated, and we have added the formula in the manuscript. Please see L208-212.

Question#15: Lines 254-255: There are still gaps – e.g. 0.5995. I suggest e.g. 0.2 ≤ small < 0.6; 0.6 ≤ moderate < 1.2.

Responds: Thank you for your suggestion. We have made changes based on comments. Please see L269-270.

Question#16: Lines 260-265: this information should be in the participants section of the Methods.

Responds: We are very grateful to the reviewers for their suggestions. We have added the information from this section to the Methods section. Please see L169-172.

Question#17: Line 267: No criteria were given in the Methods for determining moderate or excellent reliability.

Responds: We refer to the definition criteria of moderate and excellent reliability in the studies of Koo et al [1] and Cormack et al [2]. Briefly, ICC values less than 0.5 are indicative of poor reliability, values between 0.5 and 0.75 indicate moderate reliability, values between 0.75 and 0.9 indicate good reliability, and values greater than 0.90 indicate excellent reliability. A CV of ≤10% was set as the criterion to declare a variable as reliable. A 10% CV cut-off may encourage the examination of variables other than those possessing the highest reliability in future research. We added the relevant content in Methods. Please see L262-266.

[1] T.K. Koo, M.Y. Li, A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research, Journal of chiropractic medicine, 15 (2016) 155-163.

[2] S.J. Cormack, R.U. Newton, M.R. McGuigan, T.L. Doyle, Reliability of measures obtained during single and repeated countermovement jumps, International journal of sports physiology and performance, 3 (2008) 131-144.

Question#18: Line 276: Please do not say ;tended to increase’ if it was not significant.

Responds: Thank you for your suggestion. We have corrected the inappropriate representation. Please see L299.

PLoS One. doi: 10.1371/journal.pone.0277432.r005

Decision Letter 2

Laurent Mourot

14 Sep 2022

PONE-D-22-02783R2Flywheel eccentric overload exercises versus barbell half squats for basketball players: which is better for induction of post-activation performance enhancement?PLOS ONE

Dear Dr. Sun,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses all the points raised during the review process. Please submit your revised manuscript by Oct 29 2022 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

We look forward to receiving your revised manuscript.

Kind regards,

Laurent Mourot

Section Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: (No Response)

Reviewer #3: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Partly

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: No

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #3: Yes

**********

6. Review Comments to the Author

Reviewer #1: Abstract:

L 53: I suggest the authors to precise what time points are considered here? Is it only immediately after exercise, or at all time points? The sentence is misconducting.

L 57-59: was there a difference between FEOL and BHS at baseline? Please amend.

L60-62: the use of stage I and II is unclear here, and does not refer to one of the objectives stated previously. I suggest to remove this information in the abstract to make it clearer.

L 64-65: this sentence is unclear. If no change on sprint speed was observed after the two training protocols, therefore there was no effect. Please rephrase to make this sentence less confuse.

L 70: would you mean FEOL training?

Introduction

L 79: I suggest to consider rephrasing into “enhancement in explosive sport performance”

L 93: replace for “contractility” or “contractile function” depending on the meaning of your sentence

Methods

L 130: “and in stage-II, they crossed over…”

L 135: “were set before training, …”

L 169: it is unclear whether the 6 players dropped out because of injuries occurring during the experimental protocol, or were not included because of the inclusion criteria (line 158). Please be consistent throughout the paragraph.

L 179: as mentioned in a previous revision, the InBody 370 is a body composition analyzer, and could therefore not measure participant’s height. Please indicate the scale used to measure this variable.

L 198: words are lacking here, following what?

L 224: “On the GO signal” could be better

Results

The same problem still remains in this third version of the manuscript about interpretation of the statistical analysis. Authors should carefully translate their result, and mentioned difference, increase or decrease when statistics prove it. When no statistical difference is findings, therefore there is no increase or decrease of the variables, even if the numbers are not the same. This misconducting makes the results fallacious and decrease the quality of the manuscript. A real effort should be provided here to describe clearly and decently these findings.

Table 1: “indicates significant difference” or “differ significantly “. Under the present form this sentence is unclear

Discussion

L 422-426: the summary of the main findings is unclear. The first sentence states that no performance improvement was noted for CMJ and sprint after the two protocols. The second sentence argues that FEOL training can increase jump height to a greater extent that BHS. These sentences, under the present form, are therefore contradictory. Would the authors say that jump heights at 3, 6 9 and 12 min were greater for FEOL than BHS? If yes, then rephrase to correspond.

L 434-435: please state clearly how this performance could be impacted? Improvement? Decrease?

L 450: as state previously for results section, in absence of statistical difference, no difference exists. Please correct to correspond.

Reviewer #3: The majority of my previous comments have been addressed. Thank you. I only have two remaining comments:

Comment 1: Thank you for your response regarding the low/medium/high intensity for each exercise. I understand that they are not intended to be equivalent intensities between exercises. However, your use of an ANOVA may dictate that they are considered to be equal. For example, does this statistical model assume that you have 3 intensities (low/medium/high) at each of 2 exercises, and then compare? The main and especially the interaction effects may depend on this assumption, so it is worth stating/discussing. If this test is not performed then it is less of an issue, but perhaps giving the exact intensity in tables and results would be better than referring to two different ‘low’, two different ‘medium’, etc. is they are not equivalent.

Comment 2: Please check your equations in lines 210-212. I get different answers using these compared to standard equations. It is also not clear to me why flight time is divided by 1000 (instead of 2). If it is recorded in ms instead of s then this should be clear. I suggest indicating that the PPO is an estimate and not a measurement. If possible, I also suggest using g as 9.81 instead of 9.8.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #3: No

**********

PLoS One. 2022 Nov 21;17(11):e0277432. doi: 10.1371/journal.pone.0277432.r006

Author response to Decision Letter 2

29 Sep 2022

Dear editor and dear reviewers

Regarding the manuscript ID (NO.PONE-D-22-02783) entitled " Eccentric overload exercises versus loaded half squats for basketball players: which is better for induction of postactivation potentiation?". Thank you for your letter and the reviewers' comments on our manuscript entitled " Eccentric overload exercises versus loaded half squats for basketball players: which is better for induction of postactivation potentiation?" (NO.PONE-D-22-02783) were evaluated. These comments were valuable and helpful to us in revising and improving the paper, as well as important guidance for our research. We have carefully studied these comments and made revisions, which we hope will be approved by all of you. The revised parts are marked in red in the thesis. The main corrections in the paper and the responses to the reviewers are listed below.

Reply to the first reviewer as follows:

Question#1: Abstract: L 53: I suggest the authors to precise what time points are considered here? Is it only immediately after exercise, or at all time points? The sentence is misconducting.

Responds: Thank you very much for your valuable advice. We have made changes to the relevant content.Please see L53.

Question#2: L60-62: the use of stage I and II is unclear here, and does not refer to one of the objectives stated previously. I suggest to remove this information in the abstract to make it clearer.

Responds: Thank you for your valuable advice. We have removed this information from the Abstract.

Question#3: L 64-65: this sentence is unclear. If no change on sprint speed was observed after the two training protocols, therefore there was no effect. Please rephrase to make this sentence less confuse.

Responds: Thank you for your valuable advice. We have made changes to the relevant content.Please see L65-66.

Question#4: L 70: would you mean FEOL training?

Responds: Thanks for the tip. We have made changes to the relevant content.Please see L73.

Question#5: Introduction: L 79: I suggest to consider rephrasing into “enhancement in explosive sport performance”

Responds: We have made changes to the relevant content.Please see L82.

Question#6: L 93: replace for “contractility” or “contractile function” depending on the meaning of your sentence

Responds: Thank you for your valuable advice. We have made changes to the relevant content. Please see L96.

Question#7: Methods: L 130: “and in stage-II, they crossed over…”

Responds: Thank you for your prompt. We have revised the relevant content. Please see L135-136.

Question#8: L 135: “were set before training, …”

Responds: Thank you for your tip. We have revised the relevant content. Please see L140.

Question#9: L 169: it is unclear whether the 6 players dropped out because of injuries occurring during the experimental protocol, or were not included because of the inclusion criteria (line 158). Please be consistent throughout the paragraph.

Responds: Thank you very much for your valuable advice. We have revised the relevant content. Please see L164.

Question#10: L 179: as mentioned in a previous revision, the InBody 370 is a body composition analyzer, and could therefore not measure participant’s height. Please indicate the scale used to measure this variable.

Responds: Thank you very much for your valuable advice. We have revised the relevant content. Please see L184-185.

Question#11: L 198: words are lacking here, following what?

Responds: Thank you for your suggestion. We have changed the inappropriate expression. Please see L204-206.

Question#12: L 224: “On the GO signal” could be better

Responds: Sorry. We have made changes to the inappropriate statements. Please see L232.

Question#13: Results: The same problem still remains in this third version of the manuscript about interpretation of the statistical analysis. Authors should carefully translate their result, and mentioned difference, increase or decrease when statistics prove it. When no statistical difference is findings, therefore there is no increase or decrease of the variables, even if the numbers are not the same. This misconducting makes the results fallacious and decrease the quality of the manuscript. A real effort should be provided here to describe clearly and decently these findings.

Responds: We have revised it according to your valuable suggestion. Please see L56-60, L324-329, L340-342, L344-349, L359-362, L364-366, L373-375, L390-392, L412-415, L423-425, and L430-431.

Question#14: Table 1: “indicates significant difference” or “differ significantly “. Under the present form this sentence is unclear

Responds: We have revised it according to your valuable suggestion. Please see Table 1.

Question#15: Discussion

Responds: We have revised it according to your valuable suggestion. Please see L444-446.

Question#16: L 434-435: please state clearly how this performance could be impacted? Improvement? Decrease?

Responds: We apologise for our inappropriate statement. This part is speculation on our part and we are not sure whether these factors actually have an impact on sports performance. What we were actually trying to convey was the advantage of the current crossover design. We have amended this. Please see L452-458.

Question#17: L 450: as state previously for results section, in absence of statistical difference, no difference exists. Please correct to correspond.

Responds: Thank you for your valuable advice. We have revised the relevant content. Please see L311, and L470-471.

Reply to the third reviewer as follows:

Question#18: Thank you for your response regarding the low/medium/high intensity for each exercise. I understand that they are not intended to be equivalent intensities between exercises. However, your use of an ANOVA may dictate that they are considered to be equal. For example, does this statistical model assume that you have 3 intensities (low/medium/high) at each of 2 exercises, and then compare? The main and especially the interaction effects may depend on this assumption, so it is worth stating/discussing. If this test is not performed then it is less of an issue, but perhaps giving the exact intensity in tables and results would be better than referring to two different ‘low’, two different ‘medium’, etc. is they are not equivalent.

Responds: Thank you for asking the rigorous questions. At the outset of the design, it was noted that the comparison of the two devices for the semi-squat exercise would be the biggest challenge of this thesis. We have categorised the intensity according to the flywheel rotational inertia attached to the equipment as low (0. 015 kg∙m2), medium (0.035 kg∙m2) and high (0.075 kg∙m2), referencing the Petersen J,et al.[1] literature. In addition, the intensity was adjusted to low (40%), medium (60%) and high (80%) according to the number of sets, repetitions and individual 1RM, Gourgoulis V,et al.[2] ,Fukutani A.[3] ,Buscà B,et al.[4] , and other literature. We agree with you and do assume that they are equal, but in reality they are not. We will follow your suggestion to note the corresponding strengths in numerical form for modification.Please see L63-65, L68-69, L125-126, L142-143, L307-309, L315-317, L319-324, L338-339, L364, L386-389, L394-396, L419-421, L489-491, L521.

[1]Petersen J, Thorborg K, Nielsen MB, Budtz-Jørgensen E, Hölmich P. Preventive effect of eccentric training on acute hamstring injuries in men's soccer: a cluster-randomized controlled trial. Am J Sports Med. 2011 Nov;39(11):2296-303. doi: 10.1177/0363546511419277. Epub 2011 Aug 8. PMID: 21825112.

[2] Gourgoulis V , Aggeloussis N, Kasimatis P, et al. Effect of a submaximal half-squats warm-upprogram on vertical jumping ability[J]. J Strength Cond Res, 2003, 17(2):342-344. doi: 10.1519/1533-4287(2003)017<0342:eoashw>2.0.co;2

[3] Fukutani A, Takei S, Hirata K, et al. Influence of the intensity of squat exercises on thesubsequen jump performance[J]. J Strength Cond Res, 2014, 28(8):2236-2243. doi:10.1519/JSC.0000000000000409.

[4] Buscà B, Aguilera-Castells J, Arboix-Alió J, Miró A, Fort-Vanmeerhaeghe A, Peña J. Influence of the Amount of Instability on the Leg Muscle Activity During a Loaded Free Barbell Half-Squat. Int J Environ Res Public Health. 2020 Oct 31;17(21):8046. doi: 10.3390/ijerph17218046. PMID: 33142906; PMCID: PMC7672597.

Question#19: Please check your equations in lines 210-212. I get different answers using these compared to standard equations. It is also not clear to me why flight time is divided by 1000 (instead of 2). If it is recorded in ms instead of s then this should be clear. I suggest indicating that the PPO is an estimate and not a measurement. If possible, I also suggest using g as 9.81 instead of 9.8.

Responds: Thank you for your valuable advice. We have specified the unit ms in flight time and have used the PPO as an estimate rather than a measurement as you suggested, which has been very enlightening. Also changed the gravity (g) to 9.81 m/s. Please see L216-219.

We gratefully appreciate for your valuable suggestion

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.

Once again, thank you very much for your comments and suggestions.

Yours sincerely,

Jian Sun, School of Athletic Training, Guangzhou Sport University, Guangzhou, P.R. China, E-mail: sunjian@gzsport.edu.cn . Tel:+8613728059899

Attachment

Submitted filename: Responds to Reviewers.docx

Click here for additional data file.^{(22.9KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0277432.r007

Decision Letter 3

Laurent Mourot

24 Oct 2022

PONE-D-22-02783R3Flywheel eccentric overload exercises versus barbell half squats for basketball players: which is better for induction of post-activation performance enhancement?PLOS ONE

Dear Dr. Sun,

Statistical considerations still persist and it is of the uptmost importance to properly take into account reviewer's comments.

Please submit your revised manuscript by Dec 08 2022 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

We look forward to receiving your revised manuscript.

Kind regards,

Laurent Mourot

Section Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #3: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: (No Response)

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: (No Response)

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: (No Response)

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: (No Response)

Reviewer #3: Yes

**********

6. Review Comments to the Author

Reviewer #1: (No Response)

Reviewer #3: My previously recommended revisions have again mostly been addressed. I have one comment remaining which I believe represents a major assumption within the manuscript. The authors recognise this but it should be made clear throughout the article.

You have confirmed within your response that the statistical analysis treats both exercises as having equal low, medium, or high resistance. The results are therefore inherently based on the degree to which the intensities are well matched. You recognised this within your reviewer response, but I believe it should be made clear throughout all sections of the manuscript so that (potentially uninformed) readers can make their own interpretation of the results based on this assumption.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #3: No

**********

PLoS One. 2022 Nov 21;17(11):e0277432. doi: 10.1371/journal.pone.0277432.r008

Author response to Decision Letter 3

26 Oct 2022

Dear editor and dear reviewers

Regarding the manuscript ID (NO.PONE-D-22-02783) entitled " Eccentric overload exercises versus loaded half squats for basketball players: which is better for induction of postactivation potentiation?". Thank you for your letter and the reviewers' comments on our manuscript entitled " Eccentric overload exercises versus loaded half squats for basketball players: which is better for induction of postactivation potentiation?" (NO.PONE-D-22-02783) were evaluated. These comments were valuable and helpful to us in revising and improving the paper, as well as important guidance for our research. We have carefully studied these comments and made revisions, which we hope will be approved by all of you. The revised parts are marked in red in the thesis. The main corrections in the paper and the responses to the reviewers are listed below.

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #3: (No Response)

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: (No Response)

Reviewer #3: Yes

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: (No Response)

Reviewer #3: Yes

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: (No Response)

Reviewer #3: Yes

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: (No Response)

Reviewer #3: Yes

6. Review Comments to the Author

Reviewer #1: (No Response)

Responds: We agree with you so much that we have revised the text. Please see L138-140, L486-490.

Attachment

Submitted filename: Responds to Reviewers.docx

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