Exploring the acute affective responses to resistance training: A comparison of the predetermined and the estimated repetitions to failure approaches

Hadar Schwartz; Aviv Emanuel; Isaac Isur Rozen Samukas; Israel Halperin

doi:10.1371/journal.pone.0256231

. 2021 Aug 18;16(8):e0256231. doi: 10.1371/journal.pone.0256231

Exploring the acute affective responses to resistance training: A comparison of the predetermined and the estimated repetitions to failure approaches

Hadar Schwartz ^1,², Aviv Emanuel ^1,^2,³, Isaac Isur Rozen Samukas ^1,², Israel Halperin ^1,^2,^*

Editor: Daniel Boullosa⁴

PMCID: PMC8372906 PMID: 34407124

Abstract

Background

In resistance-training (RT), the number of repetitions is traditionally prescribed using a predetermined approach (e.g., three sets of 10 repetitions). An emerging alternative is the estimated repetitions to failure (ERF) approach (e.g., terminating sets two repetitions from failure). Despite the importance of affective responses experienced during RT, a comparison between the two approaches on such outcomes is lacking.

Methods

Twenty women (age range: 23–45 years) without RT experience completed estimated one repetition maximum (RM) tests in four exercises. In the next two counterbalanced sessions, participants performed the exercises using 70%1RM. Participants completed ten repetitions in all three sets (predetermined condition) or terminated the sets when perceived to be two repetitions away from task-failure (ERF condition). Primary outcomes were affective-valence, enjoyment, and approach-preference and secondary outcomes were repetition-numbers completed in each exercise.

Results

We observed trivial differences in the subjective measures and an approximately even approach-preference split. Under the ERF condition, we observed greater variability in repetition-numbers between participants and across exercises. Specifically, the mean number of repetitions was slightly lower in the chest-press, knee-extension, and lat-pulldown (~1 repetition) but considerably higher in the leg-press (17 vs. 10, p<0.01).

Conclusions

Both approaches led to comparable affective responses and to an approximately even approach preference. Hence, prior to prescribing either approach, coaches should consider trainee’s preferences. Moreover, under the ERF condition participants completed a dissimilar number of repetitions across exercises while presumably reaching a similar proximity to task-failure. This finding suggests that ERF allows for better effort regulation between exercises.

Introduction

The number of repetitions to complete per set and exercise is one of the key variables in designing and prescribing resistance-training (RT) programs. Professional organizations, such as the American College of Sports Medicine, advocate the prescription of a fixed and predetermined number of repetitions before session or set initiation (e.g., three sets of 10 repetitions) [1, 2]. In an attempt to personalize the loads to be lifted, trainees are instructed to use a certain percentage of their predetermined or predicted one repetition maximum (1RM), which is the heaviest load they can lift once (e.g., 70% of 1RM) [1, 2]. However, studies report considerable variability in the number of repetitions trainees can complete to task failure (TF) even when using the same percentage of 1RM [3, 4]. Note that here we refer to TF as an umbrella term that includes not being able to complete another repetition despite attempting to (also known as "momentary failure"), or not attempting the next repetition assuming it could not be completed (also known as "repetition maximum") [5]. Considering the variability in repetitions to TF, using a predetermined number could lead to different proximity to TF [3, 4] resulting in different perceived effort [6] and possibly dissimilar training outcomes.

To illustrate, consider two trainees instructed to complete ten repetitions in a given exercise using 70% of 1RM. One trainee can complete 20 repetitions to TF, so terminating the set after ten repetitions will correspond to a reserve of ten repetitions before reaching TF. Conversely, the other trainee can only complete eight repetitions, so the predetermined goal could not be achieved, and the set will terminate at TF. Terminating sets at different proximities to TF requires different levels of actual effort (i.e., terminating a set further away from TF requires relatively less effort compared to a set terminated at a closer proximity to TF). Reaching different levels of actual effort in RT influences trainees’ ratings of perceived exertion (RPE) [6], affective [7–9] and physiological [10–12] responses. Those differences could alter exercise-adaptations [13] and psychological outcomes such as perceptions of autonomy and competence [14]. For example, trainees might feel unchallenged or bored in case they are prevented from fulfilling the repetitions potential of the set (i.e., by a fixed number of repetitions) [15], or stressed and incompetent in the case they are pushed to premature TF (i.e., if they cannot complete the fixed number of repetitions due to natural variability in abilities) [14, 16]. These responses, in turn, may also influence the likelihood of adherence to RT programs [17]. Therefore, there is a need to explore repetition prescription strategies that can better account for individual differences in affective responses to RT.

An emerging alternative to the predetermined approach is to prescribe the number of repetitions relative to TF (e.g., terminating a set two or three repetitions away from TF). This approach has been implemented using the Estimated Repetitions to Failure (ERF) [18], and the Repetitions in Reserve (RIR) scales [19] which share similarities. Here, we will use the term ERF as it better represents the methodology we employed. ERF holds the potential to better regulate intensity of effort [18, 19] and possibly the affective responses it elicits. First, using the ERF approach can better account for individual abilities as there is no restriction upon the number of repetitions to be completed as long as one reaches the specific proximity to TF. Second, the ERF approach might lead to more positive experiences in RT sessions as it may elicit a greater sense of control over one’s actions (i.e., autonomy) [e.g., 16, 17]. Allowing people to control their actions by providing them with certain choices regarding their surrounding increases psychological well-being [14, 20, 21] and positive affective responses [22]. Since trainees decide when to terminate a set based on their perceived distance from TF, it can be viewed as an autonomy-supportive process. The latter is of great importance as positive affect experienced in a range of activities, including RT, is correlated with future intention and adherence to exercise [17, 22, 23]. Given that only 30% or less of the world’s population are meeting the general RT recommendations [24–26], exploring how ERF influences affective responses is also of public health value.

A growing number of studies [27–31], including a recent meta-analysis [32] have examined trainees’ ERF predication accuracy, as well as the long term effects of following ERF on strength and power production among different populations [33–36]. However, despite its potential to influence various psychological outcomes, excluding a few examples [34, 37], the topic remains relatively underexplored. In view of the limited research on this topic, the primary aim of this study was to explore the effects of the ERF, and the predetermined RT prescription approaches, on acute affective responses measured during and after RT sessions, among a cohort of women inexperienced in RT. The secondary aim was to compare the number of repetitions completed under the two conditions in different exercises. To achieve these goals, we implemented RT sessions that are representative of how both approaches are commonly used in practice (i.e., exercise selection [34, 38], loads [2, 7, 22], predetermined repetition numbers and sets [2, 39]). We estimated that under the ERF condition the affective responses will be more positive and that the number of repetitions will vary to a greater extent within participants, as opposed to the predetermined condition.

Materials and methods

Study design

This was a randomized, counterbalanced, within-subject, cross-over design. Participants first attended a 1RM prediction session, followed by two experimental conditions. In the predetermined condition, the number of repetitions was fixed to ten for all sets in four exercises: leg-press, knee-extension, chest-press and lat-pulldown. In the ERF condition, participants were instructed to terminate the set when they estimated to be two repetitions away from TF. This value was selected as it was expected to be demanding enough to be aligned with common RT recommendations [1, 19], yet not overly demanding leading to negative affect or physiological experiences (e.g., fatigue or discomfort) [40].

Participants

A sample of 22 healthy women with extensive Pilates experience but without RT experience volunteered to participate in this study of which 20 completed all three sessions (Table 1). We selected this sample since we were interested in the responses of women, who are often under-represented in RT studies [41]. Moreover, since inexperienced trainees are less adherent to RT, investigating this population segment is of added value [42]. We decided upon 22 participants as we were aware of our recruitment abilities and resources [43]. Nevertheless, this sample size is common in exercise science studies in which discoveries of non-null effects often occur. Inclusion criteria were age 18–45, no former orthopedic injuries and no former experience in RT. We excluded pregnant women, injured women and those who reported any RT experience. Participants’ background in physical activity consisted of Pilates, aerobic exercise, and dance. All participants were informed of the benefits and the risks of the investigation prior to signing the informed consent form on the first session. Two participants dropped out after the first session due to physical inconvenience experienced during the session. This study was approved by Tel Aviv University Ethics Committee (number 0001540–1).

Table 1. General demographics.

Age	34.4±6.5 (23–45)
Height (cm)	162.0±5.6 (151–172)
Weight (kg)	58.6±9.0 (44–74)
BMI	22.5±2.8 (19–29)
Weekly training sessions (non-RT)	3.1±0.9 (2–4)
5RM Leg Press (kg)	83.1±19.9 (50–120)
Predicted 1RM (kg)	93.5 ±22.4 (56–135)
5RM Knee Extension (kg)	51.1±10.6 (32–72)
Predicted 1RM (kg)	57.5±12.0 (36–82)
5RM Chest Press (kg)	32.0±9.8 (20–52)
Predicted 1RM (kg)	36.0±11.0 (22–60)
5RM Lat Pull Down (kg)	27.1±8.5 (13–40)
Predicted 1RM (kg)	30.5±9.6 (14–45)

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Female participants (N = 20). Values are presented as mean±SD (range)

Procedures

Participants completed three sessions (a single 1RM prediction session and two experimental conditions) with a minimum of three days apart (mean days interval between sessions: 6.2, range: 3–14). Each session consisted of four exercises performed on standard weight-stack machines: 1) leg-press (60° inclination), 2) chest-press (Technogym, Barcelona, Spain), 3) knee-extension, and 4) lat-pulldown (Life Fitness, Illinois, USA). These exercises were selected as they target the major muscle groups of both the upper and lower body. Exercise order was blocked-randomized so that leg-press was always performed prior to knee-extension. The assigned sequence was consistently performed by each participant and the equipment settings were recorded and maintained throughout the experimental sessions. Exercise execution and form were maintained throughout the sessions. This included consistent hand and feet placement, seat heights, and joint angles, in addition to repetition duration (approximately one second concentric phase and two seconds eccentric phase) in all exercises, which were confirmed by the experimenter across all sessions. Participants were asked to refrain from a strenuous exercise session on the day before sessions. They were also asked to have a fair night sleep and a light meal approximately two hours before sessions. All data were collected by the same two experimenters, at approximately the same time of day (±2 hours), with a consistent room temperature of 22 degrees Celsius.

Self-report measures

Affective valence was measured via the Feeling Scale (FS), an eleven points bipolar scale ranging from +5 (’very good’) through zero (’neutral’) to -5 (’very bad’) [44]. The experimenter presented the scale to the participants before and after each set asking the question: "How do you feel?" (also written at the top of the scale). Enjoyment was measured at the end of each session using the Exercise Enjoyment Scale, a seven-points Likert scale ranging from 1 (’not at all’) to 7 (’extraordinarily’) [45]. The experimenter presented the scale to the participants asking the question: "How much did you enjoy the exercise session?" (also written at the top of the scale). At the end of the third session, the experimenter asked participants the question: "If you had to choose one of the two conditions for your future workouts, which one would you prefer and why?". The experimenter documented participants’ answers via a tape-recorder. Participants’ responses were transcribed to a data file, translated to English, and edited for coherence by the first author. The same question was introduced to participants again 48 hours later via a text message to allow for short-term effects of the last experimental condition to fade (e.g., arousal, heartrate, etc.). After receiving the responses, we examined if any preference changes occurred. If a participant changed her mind, we coded her last response for analysis and documented any additional qualitative information in a designated column on our data file. We then aggregated the data and extracted the underlying preference themes, in line with Halperin et. al. [46]. All single-item scales went through common validation procedures prior to implementation [8].

1RM prediction and familiarization (session 1)

Participants were briefed about the general study design, signed all required forms, were weighed, and familiarized with the self-report scales. They were then instructed to perform a five-minutes warmup walk on a treadmill at a self-selected pace, followed by a general warmup consisting of dynamic stretching and calisthenics exercises. This warmup was identical in all experimental sessions. Then, a 5RM prediction protocol took place based on Brzycki’s prediction equation [47]. We used this approach as the Brzycki prediction equation commonly leads to accurate 1RM and since lifting lighter loads can be less intimidating for inexperienced trainees [48, 49]. Participants performed two warmup sets of eight to ten repetitions using a light load which was selected by the experimenter. Participants then performed sets of five repetitions with increasing load until TF was reached. Roughly two minutes of rest were provided between sets. We decided on this rest period to keep the length of this session within a reasonable timeframe, and in view of other studies that have used similar, or shorter rest periods, when implementing 1RM prediction protocols [50]. The maximal load for five repetitions was typed into a web-based calculator (www.ExRx.net) where 1RM prediction values and derivative percentages were calculated. This protocol was repeated for all exercises, in the same order assigned to each participant (see above), with three-minutes of rest between them. To gain familiarity with the FS, participants rated it before and after a few sets.

Experimental conditions (sessions 2–3)

Participants were first reminded of the single-item scales and performed the general warmup protocol. Thereafter, two specific warmup sets were performed using a light weight selected by the experimenter prior to each exercise (eight to ten repetitions) with approximately one-minute rest between them. Then, three sets were performed using 70% of participants’ predicted 1RM, with two-minutes of rest between each set. Three minutes of rest were provided between the different exercises. In the predetermined condition participants were instructed to perform ten repetitions in each set, whereas in the ERF condition, they performed as many repetitions as required until they felt they were two repetitions away from TF. FS scores were collected before and ~5 seconds after each set in both conditions whereas enjoyment scores were collected after each session. Finally, the open-ended question of preference was presented at the end of the third session in person and 48 hours later via a text message.

Statistical analyses

Excluding the preference outcome and number of repetitions completed in the predetermined condition, we inspected the normality of the data via kurtosis and skewness inspection, in which skewness < 2 and kurtosis > 7 were considered as substantial deviations from normality [51]. Unless noted otherwise, data is presented as means ± standard deviation (SD). Single item scales were treated as continuous variables following the recommendations of Rhemtulla et al. [52]. We compared the FS scores between the two conditions using the mean absolute scores across sets and exercises, and the mean difference in FS scores (by subtracting the post-set score from the pre-set score for each set in each exercise) using paired t-tests. To further examine the effects of sets, exercises, condition, and their interactions on FS ratings after each set, while holding constant the level of FS ratings before sets-initiation, we tested a mixed regression model of the following form with a random intercept (nested within participants):

Post-set F S ~ c o n d i t i o n X s e t X e x e r c i s e + Pre-set F S

We compared the mean overall enjoyment levels in each condition using paired t-tests. We tested whether the proportion of approach preferences significantly differed from what is expected by chance (0.50) using a binomial test. We compared the mean number of repetitions performed in the ERF condition relative to the fixed ten repetitions in the predetermined condition using a one sample t-test.

Both p-values and 95% confidence intervals (CIs) were calculated and reported for all outcomes. Cohen’s d effect sizes were reported when appropriate. For the FS and enjoyment outcomes we calculated Cohen’s d as $\frac{M_{d i f f}}{\sqrt{\frac{S_{p r e d}^{2} + S_{E R F}^{2}}{2}}}$ (the mean differences divided by the average SD across conditions), and for the number of repetitions it was calculated as $t / \sqrt N$ [53]. Cohen’s d were interpreted using the following criteria: small 0.2–0.5, moderate 0.5–0.8, and large >0.8 [54]. We considered effect sizes smaller than 0.2 as trivial. Binomial and t-tests were carried out with Jamovi (version 1.2.17) and the mixed regression analysis was carried out with R (version 4.0.3) and the lme4 package.

Results

Twenty participants completed the three experimental sessions. We excluded a datum of knee-extension as it invoked knee pain in one participant and a datum of lat-pulldown of a different participant who performed the exercise on a different machine (with one rather than two pully strings), causing the load to be ~50% lighter than planned. All dependent variables were normally distributed (skewness < 2, kurtosis < 7). The mean FS scores across sets and exercises was slightly higher in the predetermined (3.29±0.89) compared to ERF (3.01±0.95) condition (95%CI [0.09, 0.46], p = 0.006, ES = 0.29). (Fig 1). The mean difference of the pre-post FS scores were comparable in the predetermined (0.27±0.72) and ERF (0.18±0.80) conditions (95%CI [(-0.10,0.30], p = 0.331, ES = 0.13). Table 2 presents the mixed regression results examining the effects of sets, exercises, condition, and their interactions on FS ratings after each set, with the pre-set level of FS rating held constant.

Fig 1 — Note that n = 20 for the leg-press and chest-press and n = 19 for the knee-extension and the lat-pulldown. *ERF- Estimated Repetitions to Failure; Pred- Predetermined; FS- Feeling Scale*.

Table 2. Mixed model regression results.

Variable	Estimate (b)	SE	t-statistic (df)	p-value	95% CI
Condition (ERF vs. Predetermined)	0.19	0.22	0.87 (425)	0.383	-0.24, 0.64
Exercise (Knee-extension vs. Chest-press)	-0.40	0.22	-1.77 (425)	0.078	-0.88, 0.64
Exercise (Lat-pulldown vs. Chest-press)	0.21	0.22	0.95 (425)	0.344	-0.25, 0.68
Exercise (Leg-press vs. Chest-press)	0.10	0.22	0.45 (425)	0.656	-0.32, 0.52
Set 2 vs. Set 1	-0.01	0.22	-0.05 (425)	0.958	-0.46, 0.43
Set 3 vs. Set 1	-0.01	0.22	-0.08 (425)	0.937	-0.49, 0.40
Condition X Exercise (knee- extension)	0.06	0.32	0.20 (425)	0.845	-0.53, 0.71
Condition X Exercise (Lat-pulldown)	-0.38	0.32	-1.20 (425)	0.230	-1.01, 0.24
Condition X Exercise (Leg-press)	0.01	0.31	0.06 (425)	0.955	-0.60, 0.62
Condition X Set 2	-0.06	0.31	-0.20 (425)	0.839	-0.68, 0.53
Condition X Set 3	-0.06	0.31	-0.20 (425)	0.839	-0.65, 0.55
Exercise (knee-extension) X Set 2	0.19	0.32	0.60 (425)	0.552	-0.43, 0.82
Exercise (Lat-pulldown) X Set 2	-0.13	0.32	-0.44 (425)	0.664	-0.76, 0.50
Exercise (Leg-press) X Set 2	0.13	0.31	0.41 (425)	0.683	-0.50, 0.78
Exercise (Knee- extension) X Set 3	0.59	0.32	1.85 (425)	0.066	-0.04, 1.18
Exercise (Lat-pulldown) X Set 3	0.16	0.31	0.51 (425)	0.607	-0.44, 0.82
Exercise (Leg-press) X Set 3	0.33	0.31	1.06 (425)	0.291	-0.28, 0.93
Condition X Exercise (Knee-extension) X Set 2	0.02	0.45	0.05 (425)	0.957	-0.85, 0.88
Condition X Exercise (Lat-pulldown) X Set 2	0.25	0.45	0.55 (425)	0.583	-0.65, 1.15
Condition X Exercise (Leg-press) X Set 2	-0.21	0.44	-0.48 (425)	0.632	-1.15, 0.73
Condition X Exercise (Knee-extension) X Set 3	-0.28	.45	-0.63 (425)	.526	-1.17, 0.62
Condition X Exercise (Lat-pulldown) X Set 3	-0.18	.45	-0.59 (425)	.551	-0.70, 1.05
Condition X Exercise (Leg-press) X Set 3	-0.25	.44	-0.58 (425)	.564	-1.13, 0.55

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SE–standard error CI- Confidence interval

Mean enjoyment scores were slightly higher in the predetermined (5.70±0.80) compared to ERF (5.40±0.94) condition (95%CI [-0.04,0.6], p = 0.081, ES = 0.34). Twelve participants preferred the predetermined condition compared to eight that preferred the ERF condition (p = 0.261). We observed that participants completed less than the prescribed ten repetitions in 13% of occasions (mostly by 1–2 repetitions). Accordingly, we also compared the number of completed repetitions between conditions using paired, and one sample t-tests. Given that the results of both these tests were similar, we only report the one sample t-test results in Table 3. The number of repetitions completed by each participant in each exercise under the ERF condition is illustrated in Fig 2. Examples of participants’ responses to the open-ended question regarding their preferences are presented in Table 4. Note that only one participant changed her preference from the ERF to the predetermined condition between the end of the session to the text message (48 hours later).

Table 3. Mean ± SD values for repetitions in the ERF condition compared to the fixed ten repetitions assigned in the predetermined condition.

	Repetitions (Mean±SD)	Mean difference (95%CI)	p-value	Effect size
Overall	10.48±2.66	0.48 (-0.76, 1.73)	0.421	0.18
Leg-press	16.90±6.61	6.90 (3.80, 9.99)	<0.001	1.04
Knee-extension	8.44±2.13	-1.56 (-2.59, -0.53)	0.005	-0.73
Chest-press	7.93±1.84	-2.07 (-3.92, -1.20)	<0.001	-1.12
Lat-pulldown	8.70±2.73	-1.29 (-2.61, 0.02)	0.053	-0.47

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Mean difference, confidence intervals, p-values and Cohen’s d effect sizes are reported. Note that n = 20 for the leg-press and chest-press and n = 19 for the knee-extension and the lat-pulldown.

ERF- Estimated Repetitions to Failure

Fig 2 — Circles represent the number of repetitions performed in each exercise by each participant. *ERF*: *Estimated Repetitions to Failure*, LP: *Leg-press*, KE: *Knee extension*, CP: *Chest press*, *LatP*: *Lat pulldown*.

Table 4. Examples of participants’ responses to the question: "Which training approach did you prefer?".

Predetermined selection	ERF selection
• Selecting the number of repetitions was confusing. It made me want to quit sooner.	• It was psychologically challenging for me not to give up. The predetermined number was less challenging.
• I like to know where I am going and the endpoint of the set.	• I feel I know how to listen to my body. It feels unpleasant when I am pushed.
• When I am tired, I prefer someone telling me what to do. It makes it easier to adhere and this way I am less dependent on my mood.	• I trust I can adequately challenge myself. I know what the most suitable effort is, and the right number of repetitions for me.
• I think the instructor knows better than me. It was easier to perform this way.	• The instructor cannot identify my true state like I can during the set.

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Participants’ responses were translated from Hebrew and edited for coherence.

Discussion

In this study we compared the affective responses during RT using different repetition prescription approaches: the predetermined approach, in which the number of completed repetitions were fixed, and the ERF approach, in which participants were required to terminate the set two repetitions away from TF. The primary outcome were affective responses, collected during and after each session. We collected FS scores before and after each set, enjoyment levels experienced after each session, and participant’s approach preferences. The secondary outcome was the number of repetitions completed in each condition. Overall, we observed negligible differences between the conditions in the psychological outcomes, and some difference in the number of repetitions completed in the ERF condition. These findings shed light on the subjective experiences of trainees during RT, and point to future research directions.

In contrast to our expectation, we observed trivial to small differences between conditions in the FS and enjoyment scores, with a small trend favoring the predetermined condition. These results mostly suggest that both approaches led to similar acute affective-valence and enjoyment levels. These trivial to small differences could also stem from the study’s duration which lacked the required resolution to capture differences. The similarity in affective responses is also consistent with–and can partly explain–the approximate even split in approach preferences. Two main themes emerged when analyzing participants’ answers concerning the approach they preferred: 1) the need to have a clear set endpoint, and 2) the need to make decisions autonomously (Table 4). These two themes are also known to play important roles in motor performance [21, 55] and human motivation [14, 20]. Those who preferred the predetermined condition, might have experienced uncertainty and confusion when allowed to self-regulate the number of repetitions and therefore preferred the predetermined condition. As expressed by one participant: "This condition is more organized. Figuring out the number of repetitions on my own was confusing and felt inaccurate". Those who preferred the ERF condition may have wanted to make decisions during the RT session by regulating their effort. As expressed by another participant: "It was harder for me to perform an imposed number of repetitions. I prefer to be aware of my abilities and decide when to stop". We note that the two reasons leading participants to prefer one approach or the other are not necessarily mutually exclusive. We assume that both can co-exist, yet their relative importance differs between participants.

In the secondary analysis, the mean number of repetitions completed across exercises was comparable. However, when examining the exercises individually (Table 3), in three exercises the number of repetitions was lower in the ERF condition by approximately one repetition as opposed to the leg-press where considerably more repetitions were completed in the ERF condition (17 vs. 10). Despite completing dissimilar number of repetitions across exercises under the ERF condition, participants’ perceptions of distance from TF were similar. That is, assuming participants were able to accurately predict TF, then following ERF suggest that they reached comparable actual effort across exercises as indicated by the similar proximity to TF. Conversely, completing ten repetitions across exercises in the predetermined condition suggest that proximity to TF differed between exercises, which led to dissimilar actual effort. Hence, the ERF approach may be advantageous when the goal is to reach comparable degrees of actual effort between exercises.

While a relationship between repetitions number, distance from failure, and FS ratings has been shown to exist [8], when inspecting this relationship in the current study an unclear picture emerges. Whereas the slightly lower FS scores in the ERF condition may be related to the considerably higher repetitions completed in the leg-press, this pattern was inconsistent. This is because in the remaining three exercises FS scores were slightly lower in the ERF condition despite completing less than ten repetitions on average (see Fig 2). It is possible that this relationship was partly masked by other factors, such as the need for a clear endpoint or the need to be guided (Table 4). These results highlight the need to further inspect how different RT variables interact with one another and influence affective responses.

This study has a number of methodological aspects worthy of discussion. First, we did not verify the actual number of repetitions to TF. This decision was based on the notion that such a requirement may have been overly demanding for this cohort. Moreover, our aim was to ecologically examine the influence of different prescriptions on affective responses rather than inspect prediction accuracy. Therefore, we followed similar RT protocols, in which sets are not taken to failure [22, 39]. Second, our sample consisted of women inexperienced in RT but with experience in Pilates. It is possible that their former background and gender, influenced their estimation, affect, and preferences. This limits our ability to generalize the results of the current study to other populations. Future studies including males and completely untrained participants will shed more light on this issue. Third, we used a prediction protocol to identify 1RM and did not include a familiarization session of this protocol, both of which could have led to some inaccuracies in identifying the true 1RM. The within-subject design we implemented confirmed that all participants lifted the same loads under both experimental conditions although the high number of repetitions in the leg-press could have been a result of not reaching true 5RM in the first session. This might have caused an inaccurate prediction of 1RM and consequently more repetitions performed under the ERF condition. Finally, given that this study was a cross-over design composed of two experiential sessions, future studies should compare the different approaches in a longitudinal manner to develop a deeper understanding of the long-term implications of these prescription approaches.

Conclusion

We observed that both prescription approaches elicited similar levels of affective-valence, enjoyment, and an approximate even split of approach preferences. Approximately half of the participants preferred the predetermined approach as, according to them, it provided clear and certain endpoints, while the other half preferred the ERF approach as it heightened their sense of autonomy and control. While the mean number of repetitions across all exercises was similar, under the ERF condition participants demonstrated greater variability in repetition-numbers between participants and exercises. Since they maintained a similar proximity to TF, the invested effort across exercises was likely better standardized compared to the predetermined approach. Given these results, RT coaches can attempt to optimize the training experience by introducing both approaches and selecting one or the other based on their trainees’ preferences.

Supporting information

S1 Data

(XLSX)

Click here for additional data file.^{(40.3KB, xlsx)}

Acknowledgments

This study was conducted at the Tel Aviv University Sports Center in partial fulfillment of Hadar Schwartz’s PhD degree. The authors would like to express their gratitude to the Tel Aviv University Sports Center management and staff for their assistance.

Data Availability

All relevant data are within the paper and its Supporting information files.

Funding Statement

This study was supported by grants from the Israeli Science Foundation (1249/20) and the Marguerite Stolz Research Fund, Sackler Faculty of Medicine, Tel Aviv University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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PLoS One. 2021 Aug 18;16(8):e0256231. doi: 10.1371/journal.pone.0256231.r001

Author response to previous submission

19 Feb 2021

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PLoS One. doi: 10.1371/journal.pone.0256231.r002

Decision Letter 0

Daniel Boullosa

25 May 2021

PONE-D-21-04923

Exploring the acute affective responses to resistance training: a comparison of the predetermined and the estimated repetitions to failure approaches

PLOS ONE

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Reviewer #1: I commend the authors for conducting a well-thought experiment examining the acute affective responses to resistance training. This is an important piece of research that answers several important questions regarding resistance training prescription from a public health perspective, and highlights some avenues for future research. The manuscript is well written, ideas and methods are clearly presented, results appropriately discussed, and limitations acknowledged. However, I do have some comments which could help to strengthen the manuscript further. For more specific comments, please see below.

Abstract

Line 25-26: This parenthetical statements reads like a statement to someone, perhaps revise it to read “(e.g., termination of the sets two repetitions from failure)”, so that it’s more descriptive.

Line 33: Please replace “before” with “away from”.

Introduction

Line 56: Is there a reason why one repetition maximum is written using capital letters?

Line 76: You say “For example, feelings of boredom and monotony in the case of not fulfilling the repetitions…”. Don’t you think that feelings of boredom and monotony are more related to the long-term considerations such as exercise selection, progression schemes etc rather than some acute considerations? Regardless of whether relative effort is taken into account during RT prescription or not, a given RT program can still lead to boredom and monotony. Also, one can fail to fulfil his or her repetition potential even if the relative effort is taken into account with training prescription due to a number of other factors that are beyond our control. So, perhaps this example could be revised to include a reference to a “fixed number of repetitions” paradigm (e.g., constantly doing 3 sets of 10 can lead to …). This becomes even more relevant after reading the second part of the sentence which, to me, suggests that premature TF can happen if relative effort is not taken into account (e.g., people are instructed to do 10 reps, but they only do 8 because that’s all they can do which can then lead to disappointment). I would just revise this to better reflect problems associated with fixed repetitions as it’s obvious that you are trying to build that case in the introduction.

Line 103: I would revise “the topic remains unexamined” because you gave examples where it actually was examined, so it’s a bit contradictory. Perhaps, “…psychological outcomes, this topic remains relatively unexplored (29,32).”

Line 105: Please revise this part of the sentence as follows “… the effects of the ERF and the predetermined RT prescription approaches on acute affective responses…”.

Line 108: Please remove “the” before “different exercises”

Line 123: Please remove “e.g., muscle soreness” since muscle soreness can happen even without reaching failure – in fact, even when further away from it. Muscle soreness is also related to the familiarity – physiologically speaking – with the task, not just “difficulty”. As far as I’m concerned you don’t need an example, but if you want to provide some, I would advise going with fatigue, perception of pain or discomfort.

Lines 190-193: Perhaps, these sentences could be moved to go after describing “a 5RM test”? I believe that would follow a more appropriate sequence of events.

Statistical analysis

I’m unsure how you treated the data from all the sets? You aggregated and then compared the data from all the sets and exercises? You mention in this section that comparisons were made “by subtracting the post-set score from the pre-set score for each set of each exercise”. However, results for each set are not presented. Can you please expand on this in the manuscript?

This above also makes me wonder why you haven’t opted for a factorial design since you already measured variables of interest after every set? I completely understand if this is something that you were not interested apriori. However, even if you were not interested in the sets (apriori – which is, again, completely fine), you can still evaluate the main effect of the condition and include specific comparisons with corrections that are only related to the main effect of condition (perhaps, your main interest). This could be a more robust approach then doing a series of t-tests (regardless of the correction applied). Perhaps, this could be re-analysed and checked whether it makes a difference? Linear-mixed effects modelling is another option here, but since your design seems to be quite balanced, it would probably complicate things without adding much value.

Lines 234-236: I appreciate that you are transparent with regards to missing data, but since you used t-tests, how did you deal with missing data? Did you entirely exclude participants’ data who missed information from their knee extension and lat pulldown sessions, respectively?

Results

I’m wondering, since you already measured all the affective responses after each set of each exercise, why you didn’t report your results broken down by the exercise (and even sets)? This could have unpacked the potential effects of the number of repetitions performed in a given exercise (or set) on the affective responses. Perhaps, doing ~16 repetitions vs ~ 10 repetitions in the leg press exercise affected the psychological outcomes. For instance, if affective valence and enjoyment were not in favour for ERF condition after the leg press exercise, but they were in favour for others, one could argue that the number of repetitions completed confounded the findings. I understand that the manuscript is already packed with the information and complicating it further might not be necessary, but it might still be something worthy of consideration or discussion?

Line 224: You said that the open-ended question of preference was presented at the end of the third session in person and 48 hours later via a text message. Which one did you take for the analysis (or how did you approach data aggregation) and why?

Line 239-240: Please revise this sentence to read: “…we observed that participants completed less than the prescribed 10 repetitions in 13% of occasions (mostly by 1-2 repetitions).”

Table 4: Please check whether this response “The instructor can't identify my true state as the trainee during the set” was correct? Should it maybe say “The instructor can't identify my true state like I can do during the set” or something along these lines?

Discussion

Line 258: Please revise this sentence to read: “…we compared the affective responses during RT using different repetition prescription approaches:…”

Line 261: Please replace “was” with “were”.

Lines 286-287: Perhaps, a concluding statement indicating application of your specific findings here would strengthen the message of the paragraph?

Lines 297-299: I would remove this sentence as we don’t have enough evidence to say “most studies…”. In addition, one of the references you used (number 50) to support your statement stated the following in their practical application: “our findings suggest that RPE accuracy has a direct relationship with training experience; thus, a learning curve likely exists with novice trainees”. In that regard, it seems like we have a conflicting evidence, if nothing, so I would delete this sentence.

Lines 299-305: I believe that discussing your finding “When examining the number of repetitions completed in the predetermined condition across sets, we noted that in 13% of occasions participants completed less than the prescribed 10 (mostly by 1-2 repetitions)” would strengthen some of your arguments here even more.

Lines 306-326: I just want to compliment you here for listing all the limitations of your study (some of which might not even be a limitation given the research question). This level of honesty and consideration is not very common – respect.

Lines 333-334: Please revise this sentence to read: “While the mean number of repetitions across all exercises was similar, participants completed fewer repetitions in some exercises but considerably more in one exercise during the ERF condition”.

Ivan Jukic

Reviewer #2: Thank you for the opportunity to review this submission. This was a wonderfully simple study design addressing an important practical question that is well worth asking. I particularly appreciate the mixed methods approach which is something lacking in our field and a real strength of the work. The authors have already addressed previous concerns of other reviewers. I have some of my own suggestions below that I hope will help to improve the manuscript and feel that if these are addressed the manuscript would be a valuable addition to the literature.

My primary suggestion is to frame the study throughout in an exploratory manner given that an explicit a priori power analysis was not conducted for null hypothesis significance testing. The authors provide a very honest appraisal of their sample size justification which is often absent from most studies in the field where it is certainly the reality. It may be worth reviewing and citing this recent work from Daniel Lakens to support your resource constraint justification (https://psyarxiv.com/9d3yf/). Given this, I would also recommend removing p values from the manuscript and instead focusing on an estimation-based approach and interpretation with respect to uncertainty. I have some suggestions below for analyses and data visualisation in this manner, but in essence I would opt for reporting point and interval estimates and interpreting them cautiously and with respect to what findings may be worth following up on with confirmatory research.

On page 4 lines 76-78 - As the Rhodes and Kates article focuses on affective outcomes, you might want to offer some support that such outcomes are in fact linked to things such as boredom and autonomy in certain contexts (e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6208645/).

Page 5 lines 97-98 - Prevalence may be even less when 'resistance training' is actually parsed out from other 'muscle strengthening activities' - see discussion in https://bmcpublichealth.biomedcentral.com/articles/10.1186/s12889-017-4209-8. Also, given the female sample it is worth noting that prevalence is typically lower in women which may also give justification for this focus.

Table 1 – I would specify that training sessions refer to ‘non-RT’ training sessions.

Experimental conditions – Could you clarify here what the rest periods used were.

Statistical analyses – Not to say that what has been done here is inherently bad, but I would perhaps opt for a different approach that maximises the use of the data. I have explored the available raw data using this and feel it would probably strengthen the manuscript and also align with its exploratory nature if interpreted cautiously. The primary outcome is FS. For this given you have collected data for multiple sets, and pre and post each set, I would in essence treat this in a similar manner to an RCT with baseline adjustment using ANCOVA, but extended to a within participant design. Also, there are two fixed effects I think worth exploring in interaction with your condition effects. These are the approach-preference categorisation, and also by exercise given the different reps for the leg press. So for feeling scale I would suggest a model of the type:

post_FS ~ (condition * preference * exercise) + pre_FS + (1 | subject_num)

You would in essence have 3 observations (1 per set) for each participant for each exercise and for each condition. From this I would extract the estimated marginal means and their confidence intervals, and then would visualise using a paired estimation plot i.e. plot the paired raw data along with the emmeans and CIs for each condition. Given the exploration of preference and exercise also, I would facet by exercise (a separate panel for each), and color code the data by preference. You can produce model summary tables with fixed and random parameter estimates, p values etc for the supplementary materials if people are interested. But I would focus on the data visualisation and cautious interpretation of the estimates and their uncertainty. You could do the same for enjoyment (but obviously would just have a single data point per participant per condition). The binomial analysis of the preferences is fine as it is. I don’t anticipate any of this will materially change the overall conclusions of the manuscript, but would just better reflect these.

Page 11 line 236 – Can you elaborate on what the technical error was?

Page 15 lines 286-287 – And may also be contextual – see the paper linked above.

Limitations – One of the other reviewers drew issue with the lack of confirmation of ERF accuracy. I would note that you have looked at ecologically valid prescriptions of RT on FS etc. and the aim was not to verify prediction accuracy.

Minor:

Change ‘exercise intensity’ to intensity of effort, and also I would use ‘actual effort’ as opposed to ‘relative effort’ as in places this might be confused with the perception of effort.

Change ‘One Repetition Maximum’ to lower case throughout.

Signed: James Steele

**********

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Reviewer #1: Yes: Ivan Jukic

Reviewer #2: Yes: James Steele

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PLoS One. 2021 Aug 18;16(8):e0256231. doi: 10.1371/journal.pone.0256231.r003

Author response to Decision Letter 0

9 Jul 2021

Reviewers comments

Response: We thank the reviewer for his kind response and for his valuable comments. We addressed them point by point below.

Abstract

Response: We thank the reviewer and revised the sentence accordingly (line 25).

Line 33: Please replace “before” with “away from”.

Response: The sentence was revised accordingly (line 32).

Introduction

Line 56: Is there a reason why one repetition maximum is written using capital letters?

Response: The capital letters were removed (line 54).

Response: We thank the reviewer for this comment. We modified this part of the introduction so it introduces the possible influences of the predetermined approach as they pertain to autonomy support and the intensity of effort. Our aim was to emphasis how the fixed number of repetitions is related to different experiences and the need for individualized prescriptions which will be described in the following paragraph of the manuscript:

“Those differences could alter exercise-adaptations [13] and psychological outcomes such as perceptions of autonomy and competence [14]. For example, trainees might feel unchallenged or bored in case they are prevented from fulfilling the repetitions potential of the set (i.e., by a fixed number of repetitions) [15], or stressed and less competent in the case they are pushed to premature TF (i.e., if they cannot complete the fixed number of repetitions due to natural variability in abilities) [14,16]. These responses, in turn, may also influence the likelihood of adherence to RT programs [17].” (lines 73-79).

Response: We thank the reviewer and revised as suggested (line 105).

Line 105: Please revise this part of the sentence as follows “… the effects of the ERF and the predetermined RT prescription approaches on acute affective responses…”.

Response: We revised accordingly (line 107).

Line 108: Please remove “the” before “different exercises”

Response: We revised accordingly (line 109).

Response: We thank the reviewer for this comment and have changed the example to “fatigue and discomfort” (line 125).

Lines 190-193: Perhaps, these sentences could be moved to go after describing “a 5RM test”? I believe that would follow a more appropriate sequence of events.

Response: We thank the reviewer for this comment. We added a sentence to connect the end of the warmup to the beginning of the 5RM protocol (line 196-197).

Statistical analysis

Response: We thank the reviewer for bringing up this point. When analyzing the FS scores across conditions we aggregated the data from all three sets and compared the crude mean difference between conditions in each exercises (Figure 1). However, following both reviewers’ comments we also tested a mixed regression model which examined the effects of sets, exercises, condition, and their interactions on FS ratings after each set. See Table 3 and our following response. We now added this information to the manuscript (lines 229-236).

Response: Due to this and Reviewer 2’s comments, we tested a mixed regression model which examined the effects of sets, exercises, condition, and their interactions on FS ratings after each set (lines 232-236). Regression results are presented in Table 3.

Response: When running the t-tests for each exercise we did exclude the missing data. In the knee extension and the lat-pulldown exercises only 19 participants were analyzed. We added this information to the manuscript (Figure 1 legend and Table 3 caption).

Results

Response: We thank the reviewer for this comment. First, we created a graphic visualization of the mean FS score for each exercise between the two conditions (Figure 1). We also analyzed our data in line with the reviewers’ recommendations (Table 2). We note that there were no significant effects to any of the factors (i.e., exercise, condition or set). The possible confounding variable of repetition-numbers was also examined and although there was a significant difference for the leg press exercise, this was not a consistent finding or even a trend since in the other three exercises participants performed less than the predetermined ten repetitions with no different influence on affective responses. These data suggest that the trivial to small differences in affect that were found in favor of the predetermined condition were not related to repetition-numbers. We discuss these findings in the discussion section (lines 337-346).

Response: We thank the reviewer for this comment. We sent the question again via text message 48 hours after the last session. First, we verified that the condition preference did not change and then we checked if there was any new qualitative information regarding participants’ preference and added it to our data file in a separate column. Thereafter, we aggregated the data and extracted the main two underlying preference themes presented in Table 4 and in the discussion section (lines 311-324). Overall, there was only one participant who changed her mind. This participant’s preference changed from the ERF approach to the predetermined approach and her explanation was: “when I think about it, I prefer that the instructor will choose the number of repetitions for me, so I can have a clear target”. We now added this information to the manuscript (lines 183-189 and lines 274-275).

Line 239-240: Please revise this sentence to read: “…we observed that participants completed less than the prescribed 10 repetitions in 13% of occasions (mostly by 1-2 repetitions).”

Response: We revised accordingly (lines 267-268).

Response: We thank the reviewer for this suggestion. We now revised this sentence (Table 4).

Discussion

Line 258: Please revise this sentence to read: “…we compared the affective responses during RT using different repetition prescription approaches:…”

Response: We revised accordingly (line 294-295).

Line 261: Please replace “was” with “were”.

Response: We revised accordingly (line 297).

Lines 286-287: Perhaps, a concluding statement indicating application of your specific findings here would strengthen the message of the paragraph?

Response: We thank the reviewer and added a closing sentence to this paragraph:

“These findings shed light on the subjective experiences of trainees during RT and point to future research directions” (lines 303-304).

Response: We thank the reviewer for this comment. We removed this sentence from the manuscript.

Response: We thank the reviewer for this comment. Since this paragraph slightly changed, we respectfully decided not to include this sentence in the paragraph. See relevant changes in lines 338-347.

Response: We thank the reviewer for this comment.

Response: We revised accordingly (line 373-375).

Ivan Jukic

Response: We thank the reviewer for his kind words and for his valuable comments regarding this manuscript. Below are our detailed responses.

Response: We thank the reviewer for this comment. We now added the suggested reference of sample size justification (lines 132-133). We performed a different statistical analysis as suggested by the reviewers where we did not remove p-values but added confidence intervals for each segment as well as effect sizes when appropriate (see tables 2,3). We also aimed to emphasize the exploratory nature of this experiment throughout the manuscript (for example see lines 106, 112, 349-351).

Response: We thank the reviewer for this excellent reference. We slightly edited the paragraph and cited it in the relevant place:

Response: We thank the reviewer for this comment. We inserted this reference to support our statement (line 99).

Table 1 – I would specify that training sessions refer to ‘non-RT’ training sessions.

Response: We revised accordingly (Table 1).

Experimental conditions – Could you clarify here what the rest periods used were.

Response: Rest periods for the warmup sets were approximately one minute and two minutes between experimental sets. Three minutes rest were provided between exercises. We added this information to the manuscript (lines 213-216).

post_FS ~ (condition * preference * exercise) + pre_FS + (1 | subject_num)

Response: Due to this and Reviewer 1’s comments, we tested a mixed regression model of the form: Post-set FS ~ condition X set X exercise + pre-set FS + (1|subject_num). Regression results including 95% Cis, are presented in Table 2. We chose to replace the preference predictor with the set predictor in line with Reviewer 1’s comment, because we conducted preference measurement after the two conditions were completed. Thus, we thought it was more sensible to assume that affective state affected preferences but not vice-versa.

Page 11 line 236 – Can you elaborate on what the technical error was?

Response: The technical error occurred as a result of a human-error. The participant performed the exercise on a different machine (with one rather than two pully strings), causing the load to be ~50% lighter than planned. We added this information to the manuscript (lines 254-255).

Page 15 lines 286-287 – And may also be contextual – see the paper linked above.

Response: We thank the reviewer for this comment. Given that we added a new paragraph to the already relatively long discussion, we think that adding any additional information may take away from the key points.

Response: We thank the reviewer for this comment. We added this to the limitations section (lines 350-352).

Minor:

Change ‘exercise intensity’ to intensity of effort, and also I would use ‘actual effort’ as opposed to ‘relative effort’ as in places this might be confused with the perception of effort.

Response: We thank the reviewer for this comment. We changed exercise intensity to intensity of effort (line 87), and “relative” to “actual” effort (lines 69, 71, 332, 335, 336).

Change ‘One Repetition Maximum’ to lower case throughout.

Response: We revised accordingly.

Signed: James Steele

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PLoS One. doi: 10.1371/journal.pone.0256231.r004

Decision Letter 1

Daniel Boullosa

3 Aug 2021

Exploring the acute affective responses to resistance training: a comparison of the predetermined and the estimated repetitions to failure approaches

PONE-D-21-04923R1

Dear Dr. Halperin,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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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: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Reviewer #1: The authors are to be applauded for making significant changes to the manuscript. My comments have been adequately addressed, and the manuscript now makes a clear and significant contribution to the literature.

Ivan Jukic

Reviewer #2: Thank you for your responses and edits to both my comments and those of the other reviewer. I'm happy to endorse the submission in it's current form.

**********

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.

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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: Yes: Ivan Jukic

Reviewer #2: Yes: James Steele

PLoS One. doi: 10.1371/journal.pone.0256231.r005

Acceptance letter

Daniel Boullosa

9 Aug 2021

PONE-D-21-04923R1

Exploring the acute affective responses to resistance training: a comparison of the predetermined and the estimated repetitions to failure approaches

Dear Dr. Halperin:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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PERMALINK

Exploring the acute affective responses to resistance training: A comparison of the predetermined and the estimated repetitions to failure approaches

Hadar Schwartz

Aviv Emanuel

Isaac Isur Rozen Samukas

Israel Halperin

Roles

Abstract

Background

Methods

Results

Conclusions

Introduction

Materials and methods

Study design

Participants

Table 1. General demographics.

Procedures

Self-report measures

1RM prediction and familiarization (session 1)

Experimental conditions (sessions 2–3)

Statistical analyses

Results

Fig 1. Mean FS scores (pre and post sets) of each exercise between experimental condition.

Table 2. Mixed model regression results.

Table 3. Mean ± SD values for repetitions in the ERF condition compared to the fixed ten repetitions assigned in the predetermined condition.

Fig 2. Repetitions number performed in the ERF condition in relation to the fixed ten repetitions in the predetermined condition (continuous horizontal line).

Table 4. Examples of participants’ responses to the question: "Which training approach did you prefer?".

Discussion

Conclusion

Supporting information

Acknowledgments

Data Availability

Funding Statement

References

Author response to previous submission

Decision Letter 0

Daniel Boullosa

Roles

Author response to Decision Letter 0

Decision Letter 1

Daniel Boullosa

Roles

Acceptance letter

Daniel Boullosa

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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