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. 2025 Dec 29;20(12):e0339480. doi: 10.1371/journal.pone.0339480

Sex-based differences in front crawl and butterfly sprint performance in age-group swimmers

Radomyos Matjiur 1,#, Phornpot Chainok 1,*,#, Jessy Lauer 2,3, Weerawat Limroongreungrat 4, Karla de Jesus 5, Rodrigo Zacca 6,7,8,9, Ricardo J Fernandes 10, J Paulo Vilas-Boas 10
Editor: Dalton Müller Pessôa Filho11
PMCID: PMC12747348  PMID: 41460882

Abstract

Objectives

To identify the key variables influencing 50 m sprint performance in front crawl and butterfly strokes and determine the predominant predictors of sex-related performance differences in each technique in age-group swimmers.

Methods

Thirty national-level age-group swimmers (15 boys and 15 girls; age 13.5 ± 1.0 years) underwent assessments of anthropometry, biological maturation, neuromuscular performance (dynamic strength index of upper and lower limbs), anaerobic critical velocity, tethered swimming force, and stroke mechanics.

Results

Multivariate analyses revealed substantial sex differences (p < 0.05), with boys outperforming girls in upper-body force output and anaerobic critical velocity (AnCV). Boys showed a greater AnCV (1.54 vs. 1.45 m·s ⁻ ¹) and lower fatigue index (−8.52% in front crawl). Boys and girls had a 27.60 N front crawl force differential and 13.59 N butterfly force difference in the first 10 s of tethered swimming. Controlling for sex and biological maturity, the maximum explained variation (ƞ2) was found in front crawl tethered swimming force (47%), and butterfly lower limb neuromuscular performance (29%). In front crawl, total push-up peak force (diff: 215.44 N; 95% CI: 1.25 to 3.08; p < 0.001) and body height (diff: 0.08 cm; 95% CI: −1.82 to −0.28; p < 0.001) were key discriminators, while in butterfly, push-up force (diff: 215.44 N; 95% CI: 1.25 to 3.08; p < 0.001) and stroke index (diff: 0.54 m² ⋅ s ⁻ ¹; 95% CI: 1.04 to 2.79; p < 0.001) were the most effective predictors.

Conclusion

Our findings confirm the predictive ability of upper-limb neuromuscular performance and stroke efficiency in identifying sex-based differences in sprint swimming. The practical implications of these findings are substantial, offering a framework for coaches and sports scientists to improve procedures for training by focusing on technique- and sex-specific performance characteristics at critical stages of athletic development.

Introduction

Swimming is predominantly considered as a biophysical sport, where biomechanical and bioenergetic factors play pivotal roles in determining performance. Consequently, coaches and swimming scientists often prescribe training and evaluate physical conditioning and technical proficiency in combination, instead of assuming independent analysis [1,2]. The efficacy of swimming, especially in sprint events such as the 50 m simultaneous (butterfly), and alternated technique (front crawl), is significantly determined by a swimmer’s ability to generate force and maintain velocity throughout short distances [3–5]. While factors including swimming technique, starts and turns [6,7], along with physical and physiological endurance and energy system capacity and power are essential [1,2], the coordinated generation of propulsive force, involving strength and power in both the upper and lower limbs, is crucial in determining performance success.

Previous investigations into the variables and characteristics of propulsive force associated with swimming performance have predominantly focused on indirect assessments of land-based strength and conditioning, encompassing isokinetic evaluations, one-repetition maximum (1-RM), countermovement jump (CMJ), isometric peak torque and handgrip strength [8–14]. Direct assessments of a swimmer’s maximal strength and force production capabilities have previously involved fully-tethered [11,15] and semi-tethered swimming [16,17], alongside evaluations of anaerobic and sprint performance across four swimming techniques [9,18,19]. Still, although tethered swimming provides a direct assessment of force production [11], current research has not established the optimal balance between maximal strength and explosive power that facilitates faster and more efficient techniques, thus enhancing sprint swimming performance.

Sprint swimming is an event where variations in movement techniques, both simultaneous (breaststroke and butterfly) and alternated (front crawl and backstroke), may be emphasized and influenced by distinct primary biophysical factors, including energy and biomechanical aspects [20]. From a biomechanical perspective, the ability to enhance mechanical and propulsive efficiency could be associated with the optimization of swimming technique and the capacity to balance maximal and explosive strength, referred to as the dynamic strength index (DSI) [3,9,21,22]. Considering that DSI profiling is probably associated with the 50 m sprint swimming distance, the correlations between swimming performance and the profile components of the upper and lower limbs may differ separately between simultaneous and alternating techniques.

Consequently, biophysical factors, encompassing energy and biomechanical aspects, should not be independently examined. The complex relationship between upper and lower limb neuromuscular performance, force generation during fully-tethered swimming, anaerobic critical velocity (AnCV) and swimming performance at 50 m remains controversial, with no consensus regarding the bilateral and unilateral limbs that directly influence the biomechanics of sprint swimming particularly in age-group. Notwithstanding the apparent inconsistencies in some available results, there is a compelling imperative to enhance the development of age-group swimmers, particularly during the pubertal period, when maturity status can significantly influence a swimmer’s growth, development and performance [23]. Therefore, the purposes of this study were: (i) to conduct a multivariate analysis of age-group swimmers’ performance to determine which variables are predominant to achieve better performances when analyzing the difference between sex in two swimming techniques (front crawl and butterfly) and (ii) identify the least set of predictors that discriminate the sex differences.

With this in mind, we also intend to provide important and useful information that may help coaches, strength and conditioning and sport scientists to improve the development and understanding characteristics of propulsive force associated with swimming performance, and increase success opportunities in their training sessions and competitions. Besides, we hypothesized that differences in swimming performance across techniques are associated with a minimal set of key physiological and biomechanical predictors, specifically AnCV, tethering force, and upper and lower limb dynamic strength index (DSI).

Materials and methods

Participants

A priori power analysis was conducted using G*Power version 3.1.9.2 to determine the required sample size. The analysis indicated that a minimum of 30 participants was necessary to detect a large effect size (0.95) with a statistical power of 0.95 and an alpha level of 0.05. Accordingly, thirty national-level age-group swimmers (15 boys and 15 girls), all specializing in short-distance events and having provided written informed consent, were recruited for the study. All participants, possessed at least of three year of competition experience in regional or national competitions, underwent current medical evaluations and qualified for the national championships. Swimmers with any contraindications for study participation were excluded. No swimmers in the age group were utilizing medications or dietary supplements recognized to affect physical performance. The research complied with the standards set out by the World Medical Association’s Declaration of Helsinki, and ethics approval was granted by the local university (code number HS025/2567(C3)). The participants and their guardians were provided with a comprehensive explanation of the testing protocols before obtaining signed consent for participation.

Testing procedures

We conducted a prospective cohort study using descriptive, comparative, correlational, and multivariate analysis to assess physiological variables (i.e., AnCV), biomechanical factors (e.g., tethering force and stroke mechanics — stroke length [SL], stroke rate [SR] and stroke index [SI]) and neuromuscular performance (i.e., DSI of upper and lower limbs) affecting performance across sex and techniques. Testing was conducted during the final four weeks leading up to the National Age–Group Championships. Assessments were carried out on five separate occasions between the first macrocycle (January -April, 2025) of a traditional three-peak preparation program.

On the first visit, participants underwent a comprehensive assessment of their anthropometric data, body composition, and biological maturation. Subsequently, on the same day, a second testing session was executed, comprising a maximal 50 m front crawl swimming assessment in a 25 m pool. On the following day, the dynamic strength index (DSI) for both the upper and lower limbs was assessed. On the third day, the anaerobic critical velocity (AnCV) was assessed with maximum effort trials of 10 m, 15 m and 25 m in front crawl and butterfly, with a 30 min rest period between techniques. The fourth day included a 30 s maximal tethered swimming force assessment, conducted with a specialized tethered swimming force apparatus (Swimforce V1.0.0, Germany) for both front crawl and butterfly techniques, with a 30 min interval between the trials. Finally, an all-out 50 m butterfly swimming performance was performed in a 25 m pool at the final appointment.

Anthropometry, body composition and biological maturation

The standing height was measured using ultrasonic height meter in which automatically measures height for improved input accuracy (X-Contact 357S, Jawon Medical Co., Ltd., Korea) and body mass and body mass index (BMI; kg·m-2) were evaluated using bioelectrical impedance analysis (BIA; Body Composition Analyzer: X-Contact 357S, Jawon Medical Co., Ltd., Korea), performed by a qualified anthropometrist with over fifteen years of experience, ensuring compliance with established anthropometric measurement protocols according to the techniques described by the International Society for the Advancement of Kinanthropometry [30]. The biological maturity offset was determined by calculating the age at peak height velocity (age-at-PHV) [24]. Weight, height, seating height and sex were all factors in a specific calculation. The maturity offset is a numerical value that measures how many years an individual is away from their peak height velocity (PHV) age. A maturity offset can be positive (+) or negative (-) showing how many years the participant has been in the sport after reaching PHV and how many years the participant has to go before reaching PHV, respectively.

Neuromuscular performance

The lower-limb dynamic strength index (DSI) was calculated as the ratio of peak force during the countermovement jump (CMJ) to peak force during the isometric mid-thigh pull (IMTP), based on data extracted from their respective force-time curves [25]. The CMJ were evaluated at a 1000 Hz sample rate utilizing the commercially available K-deltas dual force platforms (Kinvent Physio, Montpellier, France). Peak force measurements from these evaluations encompassed dominant CMJ peak force (N), non-dominant CMJ peak force (N), and total CMJ peak force (N), which were utilized for further investigation. The isometric mid-thigh pull (IMTP) was performed on the K-deltas dual force platforms 60 s subsequent to the CMJ. In this test, age-group swimmers exerted maximal force by pulling a bar and pressing their feet against the force platform for 5 seconds. Peak force values, including dominant and non-dominant IMTP peak force (N), and total IMTP peak force (N) were derived from the force-time curves for subsequent analysis.

Peak forces (N) from both the CMJ and the IMTP were used for subsequent analysis of the lower limb dynamic strength index (DSI). To comprehensively assess strength characteristics, the unilateral strength asymmetry index was also calculated for both CMJ and IMTP, which serves as an evaluation of maximal isometric force. This index was determined by computing the percentage difference between the dominant (D) and non-dominant (ND) limbs. The dominant limb was methodically defined as the one that exhibited the higher peak force during the test. The asymmetry index was calculated using the following formula: (D − ND)/ D × 100 [22].

For the component of upper limb DSI, ballistic push-up and isometric grip strength were used to determine upper extremity DSI from K-deltas dual force platforms (Kinvent Physio, Montpellier, France) [25]. The ballistic push-up test was performed at a sampling rate of 1000 Hz using the K-deltas dual force platforms (Kinvent Physio, Montpellier, France). Age-group swimmers positioned their hands at approximately shoulder width on a K-deltas dual force platform and lowered their chests until contact with the plate was made [25]. The peak force measurements from this test, including Dominant push-up peak force (N), Non-dominant push-up peak force (N), and Total push-up peak force (N), were recorded for subsequent analysis. [25].

The isometric grip strength was measured using a K-Grip Dynamometer (Kinvent Physio, Montpellier, France) for a duration of 5 s, 60 s after completing the ballistic push-up, with a 30 s rest time between each side. The peak force values recorded were dominant grip strength peak force (N), non-dominant grip strength peak force (N) and total grip strength peak force (N). Peak forces (N) from the ballistic push-up and static grip strength tests were utilized for subsequent analysis for upper limb DSI. The unilateral strength asymmetry index of the ballistic push-up and static grip strength test was determined as the percentage difference between the dominant limb and the non-dominant limb as proposed by Bishop et al. [22].

Tethered swimming force

The tethered swimming force was measured using a load-cell device (Swimforce V1.0.0, Germany), which recorded data at a frequency of 100 Hz and had a maximum capacity of 1,000 N. The system was situated on a starting block 5 m distance, sloping at an inclination of 5.7° to the water surface [26]. The maximal tethered swimming tests for the whole crawl and butterfly technique were conducted in separate testing sessions. Force data was consistently gathered during a 30 s maximal effort interval. The data was subsequently imported into Acqknowledge 4.0 (BIOPAC Systems, Inc., CA, USA) and filtered with a 15 Hz cut-off digital filter (finite impulse response, FIR – Window Blackman −61 dB), as established through Fast Fourier Transform (FFT) analysis to reduce artifact noise [26]. The key force variables derived from the individual force-time curves included the mean force at each 10 s interval and the fatigue index [26,27].

Anaerobic critical velocity (AnCV)

Anaerobic performance for front crawl and butterfly swimming techniques was assessed using the AnCV method that originally adapted for swimming from the critical power concept that provides a reliable measure of an athlete’s anaerobic capacity [28,29]. This approach, widely recognized in swimming research which was calculated for each age-group swimmer by analyzing the slope of the distance-time (Dd-t) relationship, based on swimming performance times for 10, 15 and 25 m over time [28,29]. All swimming performance times for the 10 m, 15 m, and 25 m trials were meticulously recorded by two experienced researchers using Seiko S140 chronometers. To ensure exceptional inter-observer reliability, the final time utilized was the average of the two recorded measures, based upon their values not differing by more than 0.20 seconds [28,29]. A 10-minute rest period was strictly enforced between each swimming session to ensure sufficient recovery. The regression model is expressed as y = ax + b, where y denotes the distance covered and x represents time. In this context, the coefficient an is primarily recognized as the short-distance velocity coefficient (slope), while also being recognized for its conventional meaning in the literature as part of the anaerobic critical velocity (AnCV). The constant b corresponds to the y-intercept of the regression line [28,29].

Swimming performance

Age-group swimmers completed a 400 m warm-up swim, followed by a 15 min passive rest period prior to the 50 m front crawl and butterfly block all-out performance time trial. The 50 m race times were recorded by qualified timekeeper using a SEIKO S056 stopwatch (Tokyo, Japan). Results were obtained for three key kinematic variables frequently discussed in swimming biomechanics: stroke rate (SR), stroke length (SL), and stroke index (SI). SR and SL were calculated from the time it took to complete three consecutive stroke cycles. Stroke length was determined using the ratio of swimming velocity (v) to the corresponding SR, while SI was calculated by multiplying the swimming velocity (v) by the SL [30].

Statistical analysis

Descriptive statistics are presented as mean ± standard deviation (M ± sd). The normality assumption was assessed using the Shapiro–Wilk test, where no significant violations were noticed. Sex differences were firstly compared in a univariate fashion using Student t test; Cohen’s d values were also calculated and interpreted as follows: < 0.20 (trivial), 0.20 to 0.59 (small), 0.60 to 1.19 (moderate), 1.20 to 1.99 (large), 2.0 to 3.9 (very large), and > 4.0 (extremely large) [31]. Then, the effects of sex and biological maturation on anthropometric and body composition, neuromuscular performance (upper and lower limbs DSI), tethering force, AnCV and swimming technique kinematics (SI) were examined using a multivariate analysis of covariance (MANCOVA) and eta squared (ƞ2) was used as a measure of explained variance. Further, using only variables that had a statistically significant effect, a forward stepwise discriminant function analysis was employed to identify the smallest set of variables that maximizes the differences between sexes for each swimming technique. The statistical analyses were conducted using SPSS 25.0 (IBM Corp., Armonk, New York, US), significance level was established at alpha = 0.05.

Results

Descriptive statistics for age, anthropometric and body composition, biological maturation, neuromuscular performance, AnCV, tethered force and swimming performance variables of boys and girls age-group swimming in front crawl and butterfly swimming technique are shown in Table 1 and Table 2, respectively. Substantial sex differences were identified in the selected variables (p < 0.05), with the exception of the CMJ asymmetry index, ITMP asymmetry index, lower limb DSI, push-up asymmetry index, grip strength asymmetry index and upper limb DSI in both swimming techniques, as well as AnCV and SR for butterfly.

Table 1. Descriptive statistics (M ± SD) for general characteristics, anthropometry and maturation and neuromuscular performance in age-group swimmers.

Variables Boys Girls Mean difference (95% CI) Cohen’s d
M ± SD M ± SD
Age (years) 13.27 ± 0.33 13.73 ± 0.96 −0.47 (−1.23, 0.23) −0.51
50 m World aquatic point 418.80 ± 86.12 454.60 ± 87.83 −35.38 (−1.13, 0.32) −0.41
Biological maturation
Maturity offset (years) −1.37 ± 0.88 −0.43 ± 0.97 −0.93(−1.82, −0.28)* −1.01
Anthropometry and body composition
Height (cm) 1.70 ± 0.07 1.62 ± 0.05 0.08 (−1.82, −0.28)** 1.44
Body mass (kg) 60.73 ± 9.23 50.00 ± 4.33 10.73 (0.62, 2.34)** 1.48
Body mass index (kg ⋅ m-2) 20.82 ± 2.37 19.08 ± 1.60 1.74 (0.10, 1.60)* 0.86
Lower limbs neuromuscular performance
Dominant CMJ peak force (N) 750.83 ± 119.84 552.47 ± 63.24 198.37 (1.16, 2.96)** 2.07
Non-dominant CMJ peak force (N) 704.65 ± 118.12 524.52 ± 56.66 180.12(1.06, 2.81)** 1.94
Total CMJ peak force (N) 1,455.52 ± 236.26 1,076.99 ± 116.95 378.53(1.13, 2.91)** 2.03
CMJ asymmetry index (%) 6.22 ± 3.84 4.91 ± 4.55 1.31 (−0.41, 1.03) 0.31
Dominant ITMP peak force (N) 958.47 ± 273.36 712.21 ± 132.76 246.27(0.36, 1.91)* 1.15
Non-dominant ITMP peak force (N) 876.71 ± 242.81 633.31 ± 119.65 243.40(0.47, 2.05)** 1.27
Total IMTP peak force (N) 1,835.17 ± 511.89 1,344.86 ± 251.28 490.31(0.42, 1.99)** 1.22
ITMP asymmetry index (%) 8.39 ± 5.88 11.13 ± 3.70 −2.73 (−1.28, 0.18) −0.56
Lower limb DSI (%) 0.85 ± 0.27 0.82 ± 0.12 0.04 (−0.55, 0.89) 0.17
Upper limbs neuromuscular performance
Dominant push-up peak force (N) 369.01 ± 67.83 257.10 ± 37.93 111.91 (1.13, 2.92)** 2.04
Non-dominant push-up peak force (N) 328.06 ± 57.68 224.52 ± 36.17 103.54 (1.23, 3.05)** 2.15
Total push-up peak force (N) 697.07 ± 122.42 481.63 ± 68.05 215.44 (1.25, 3.08)** 2.18
Push-up asymmetry index (%) 11.61 ± 7.80 12.11 ± 10.25 −0.49 (−0.77, 0.66) −0.05
Dominant grip strength peak force (N) 304.06 ± 66.07 220.67 ± 44.17 83.39 (0.66, 2.29)** 1.48
Non-dominant grip strength peak force (N) ()(N)(N) 282.29 ± 65.45 201.62 ± 46.40 80.67 (0.61, 2.21)** 1.42
Total grip strength peak force (N) 586.35 ± 130.37 422.29 ± 90.06 164.07 (0.64, 2.27)** 1.46
Grip strength asymmetry index (%) 7.43 ± 6.01 9.03 ± 5.91 −1.67 (−0.99, 0.44) −0.28
Upper limb DSI (%) 1.24 ± 0.31 1.17 ± 0.21 0.07 (−0.47, 0.97) 0.25
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Note: CMJ = Counter movement jump; IMTP = Isometric mid-thigh pull; AnCV = Anaerobic critical velocity DSI = Dynamic strength index; (NS) = Non-significant; (*) = p < 0.05; (**) = p < 0.01; (***) = p < 0.001.

Table 2. Descriptive statistics (M ± SD) for anaerobic critical velocity (AnCV), tethered force and swimming performance in age-group front crawl and butterfly swimmers.

Variables Boys Girls Mean difference (95 % CI) Cohen’s d
M ± SD M ± SD
Front crawl
Anaerobic Critical velocity
AnCV (m⋅s-1) 1.54 ± 0.09 1.45 ± 0.07 0.08 (0.26, 1.80)** 1.04
Swimming tethered force
Average mean force (0-10s) (N) 78.92 ± 19.10 51.33 ± 15.70 27.60 (0.74, 2.39)** 1.58
Average mean force (10-20s) (N) 65.77 ± 16.37 42.49 ± 11.75 23.29 (0.79, 2.46)** 1.63
Average mean force (20-30s) (N) 53.33± 14.40 31.73 ± 9.27 21.59 (0.92, 2.63)** 1.78
Fatigue index (%) 36.62± 10.21 45.13 ± 8.31 -8.52 (-1.66, -0.15)* -0.92
Swimming performance
Average velocity (m⋅s-1) 1.78 ± 0.13 1.65 ± 0.07 0.13 (0.44, 2.02)** 1.24
Stroke rate: SR (cycles⋅min-1) 50.33 ± 3.22 47.84 ± 2.48 02.49 (0.11, 1.66)* 0.87
Stroke length: SL (m) 2.12 ± 0.17 2.07 ± 0.14 0.05 (-0.39, 1.06)** 0.34
Stroke index: SI (m2⋅s-1) 3.78 ± 0.52 3.41 ± 0.33 0.38 (0.10, 1.60)* 0.86
Butterfly
Anaerobic Critical velocity AnCV (m⋅s-1) 1.49 ± 0.14 1.42 ± 0.09 0.08 (-0.09, 1.38) 0.65
Anaerobic Critical velocity AnCV (m⋅s-1) 1.49 ± 0.14 1.42 ± 0.09 0.08 (-0.09, 1.38) 0.65
Swimming tethered force
Average mean force (0-10s) (N) 64.15 ± 15.80 50.56 ± 12.73 13.59 (0.18, 1.70)* 0.95
Average mean force (10-20s) (N) 53.81 ± 12.21 39.09 ± 5.93 14.72 (0.70, 2.34)** 1.53
Average mean force (20-30s) (N) 46.64 ± 11.56 32.34 ± 3.93 14.29 (0.81, 2.48)** 1.66
Fatigue index (%) 32.61 ± 16.18 39.37 ± 8.13 -6.75 (-1.25, 0.21)** -0.53
Swimming performance
Average velocity (m⋅s-1) 1.62 ± 0.16 1.51 ± 0.07 0.10 (0.07, 1.57)* 0.83
Stroke rate: SR (cycles⋅min-1) 53.27 ± 6.57 54.36 ± 4.89 -1.07 (-0.90, 0.53) -0.19
Stroke length: SL (m) 1.83 ± 0.16 1.68 ± 0.12 0.15 (0.31, 1.85)** 1.09
Stroke index: SI (m2⋅s-1) 3.08 ± 0.36 2.53 ± 0.17 0.54 (1.04, 2.79)** 1.93
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Note: CMJ = Counter movement jump; IMTP = Isometric mid-thigh pull; AnCV = Anaerobic critical velocity DSI = Dynamic strength index; * = p < 0.05; ** = p < 0.01; *** = p < 0.001.

When controlling for biological maturation, the MANCOVA results (Table 3) revealed significant results for each variable set only in the swimming tethered force. A total of 21 variables indicated that boys swimmers outperformed girls swimmers, with ƞ2 ranging from 23% (anthropometry and body composition) to 47% (tethered swimming force). For butterfly, the MANCOVA results (Table 4) revealed no significant results across all multivariate tests with a total of 20 variables in which boys outperformed girls swimmers and the ƞ2 varied from 7% (tethered swimming force) to 29% (lower limbs neuromuscular performance).

Table 3. Multivariate analyses of covariance (MANCOVA) with sex and maturity offset as covariates in the front crawl technique.

Variables Multivariate Test Univariate Test
F ƞ2 F ƞ2
Anthropometry and body composition 2.38 0.23
Height (cm) 23.12*** 0.47
Body mass (kg) 21.38*** 0.45
Body mass index (kg ⋅ m-2) 6.27* 0.19
Lower limbs neuromuscular performance 0.82 0.29
Dominant countermovement jump peak force (N) 33.59*** 0.56
Non-dominant countermovement jump peak force (N) 28.84*** 0.53
Total countermovement jump peak force (N) 31.77*** 0.55
Countermovement jump asymmetry index (%) 0.35 0.01
Dominant isometric mid-thigh pull peak force (N) 14.44** 0.36
Non-dominant isometric mid-thigh pull peak force (N) 17.93*** 0.41
Total isometric mid-thigh pull peak force (N) 16.33*** 0.39
Isometric mid-thigh pull asymmetry index (%) 1.97 0.07
Lower limb dynamic strength index (%) 0.13 0.01
Upper limbs neuromuscular performance 0.88 0.27
Dominant push-up peak force (N) 49.88*** 0.66
Non-dominant push-up peak force (N) 53.71*** 0.77
Total push-up peak force (N) 57.9*** 0.69
Push-up asymmetry index (%) 0.05 0.01
Dominant grip strength peak force (N) 23.19*** 0.47
Non-dominant grip strength peak force (N) 21.73*** 0.46
Total grip strength peak force (N) 22.88** 0.47
Grip strength asymmetry index (%) 0.65 0.02
Upper limb dynamic strength index (%) 0.29 0.01
Anaerobic Critical velocity (m ⋅ s-1) 14.94*** 0.37
Swimming tethered force 4.37** 0.43
Average mean force (0-10s) (N) 25.72*** 0.50
Average mean force (10-20s) (N) 27.68*** 0.52
Average mean force (20-30s) (N) 36.79*** 0.59
Fatigue index (%) 15.69*** 0.38
Swimming Performance 0.74 0.26
Average velocity (m ⋅ s-1) 20.72*** 0.44
Stroke rate (cycles⋅min-1) 2.10 0.08
Stroke length (m) 7.90** 0.23
Stroke index: SI (m2 ⋅ s-1) 18.38** 0.44
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Note: CMJ = Counter movement jump; IMTP = Isometric mid-thigh pull; AnCV = Anaerobic critical velocity DSI = Dynamic strength index; (NS) = Non-significant; (*) = p < 0.05; (**) = p < 0.01; (***) = p < 0.001.

Table 4. Multivariate analyses of covariance (MANCOVA) with sex and maturity offset as covariates in the butterfly technique.

Variables Multivariate Test Univariate Test
F ƞ2 F ƞ2
Anthropometry and body composition 2.28 0.23
Height (cm) 23.12*** 0.47
Body mass (kg) 21.38*** 0.41
Body mass index (kg ⋅ m-2) 6.23* 0.19
Lower limbs neuromuscular performance 0.82 0.29
Dominant countermovement jump peak force (N) 33.59*** 0.56
Non-dominant countermovement jump peak force (N) 28.84*** 0.53
Total countermovement jump peak force (N) 31.77*** 0.55
Countermovement jump asymmetry index (%) 0.35 0.01
Dominant isometric mid-thigh pull peak force (N) 14.41** 0.36
Non-dominant isometric mid-thigh pull peak force (N) 17.93*** 0.41
Total isometric mid-thigh pull peak force (N) 16.33*** 0.39
Isometric mid-thigh pull asymmetry index (%) 1.97 0.07
Lower limb dynamic strength index (%) 0.13 0.01
Upper limbs neuromuscular performance 0.88 0.27
Dominant push-up peak force (N) 49.88*** 0.66
Non-dominant push-up peak force (N) 53.71*** 0.67
Total push-up peak force (N) 57.96*** 0.69
Push-up asymmetry index (%) 0.05 0.01
Dominant grip strength peak force (N) 23.19*** 0.47
Non-dominant grip strength peak force (N) 21.73*** 0.46
Total grip strength peak force (N) 22.88*** 0.47
Grip strength asymmetry index (%) 0.65 0.02
Upper limb dynamic strength index (%) 0.29 0.01
Anaerobic Critical velocity (m ⋅ s-1) 6.37* 0.20
Swimming tethered force 0.40 0.07
Average mean force (0-10s) (N) 9.99** 0.23
Average mean force (10-20s) (N) 15.77*** 0.38
Average mean force (20-30s) (N) 19.33*** 0.43
Fatigue index (%) 0.66 0.23
Swimming Performance 0.91 0.09
Average velocity (m ⋅ s-1) 7.91** 0.23
Stroke rate (cycles⋅min-1) 0.04 0.01
Stroke length (m) 7.17* 0.22
Stroke index: SI (m2 ⋅ s-1) 25.74*** 0.50
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Note: CMJ = Counter movement jump; IMTP = Isometric mid-thigh pull; AnCV = Anaerobic critical velocity DSI = Dynamic strength index; * = p < 0.05; ** = p < 0.01; *** = p < 0.001.

Table 5 reports the main results of the forward stepwise discriminant function, and shows the best smaller set of the previous twenty-one variables that best discriminates the sex and are in order of importance of total push-up peak force and body height in front crawl and total push-up peak force and stroke index from the best smaller set of the previous twenty variables in butterfly, respectively.

Table 5. Summary of stepping in forward stepwise discriminant analysis in front crawl and butterfly techniques.

Step Entered Wilks’s Lambda Approx. F-Ratio p-Value
Front crawl
1 Total push-up peak force (N) 0.818 64.43 p < 0.001
2 Body height (cm) 0.457 36.85 p < 0.001
Butterfly
1 Total push-up peak force (N) 0.791 56.93 p < 0.001
2 Stroke index (m2 ⋅ s) 0.721 44.45 p < 0.001
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Discussion

This study investigated the multivariate profiles of age-group swimmers by sex in front crawl and butterfly techniques, controlling for biological development, and identified the minimal set of predictors that differentiate sexes. This study provided comprehensive evidence that growth and maturation, AnCV, tethering force and the DSI of both upper and lower limbs play pivotal roles in determining 50 m sprint swimming performance in age-group swimmers. Multivariate analysis revealed significant sex-based differences across physiological and biomechanical variables, with boys swimmers outperforming girls in several key domains, even after controlling for biological maturity. Total push-up peak force and body height distinguished sex differences in front crawl, while total push-up peak force and stroke index differentiated sex in butterfly. Thus, these findings offer support to the proposed hypotheses and also highlight the complexity of performance determinants across swimming techniques.

The present study, considering sex differences, demonstrated that boys outperformed girls on multiple anthropometric, neuromuscular, and tethered-force characteristics regularly observed in research on young swimmers [2,3,32]. In along with describing these expected differences, our findings enhance existing knowledge by identifying the most significant elements that differentiate sex-specific sprint characteristics. Beyond confirming expected sex differences, our findings enhance current knowledge by identifying the principal elements that distinctly differentiate sex-specific sprint features. Utilizing a multivariate model that incorporates growth and maturation [24], upper- and lower-limb DSI [21,22], short-distance velocity coefficients from the AnCV [28,29], tethered-force outputs [11,15] and stroke kinematics [23], we determined a minimal but highly discriminative set of variables that effectively differentiates sprint performance characteristics between boys and girls.

From the forward stepwise discriminant analysis it was identified that total push-up peak force was the strongest discriminant variable in both front crawl and butterfly techniques, highlighting the critical importance of upper-body explosive strength in short-distance sprint swimming. This metric likely reflects a combination of muscular power, interlimb coordination and neuromuscular control, all of which are essential for effective propulsion [3,9,13]. Moreover, in front crawl, body height was a secondary predictor, suggesting the added mechanical advantage of longer limbs and SL in alternating techniques [32,34].

In contrast, SI was a key differentiator in butterfly, indicating the role of stroke efficiency and fluid coordination in simultaneous techniques, which require more precise motor timing and technical control [33,38]. Moreover, the stronger discriminant power of SI in butterfly indicates that stroke efficiency and motor coordination may have heightened importance in simultaneous techniques compared to alternating ones. Therefore, training strategies for young swimmers should not only emphasize strength development but also target technique refinement, particularly in butterfly, where technical execution appears more sensitive to differentiating performance [33].

Sprint swimming, encompassed by both simultaneous (breaststroke and butterfly) and alternating techniques (front crawl and backstroke), is determined by different important biophysical components, including energy and biomechanical elements [20]. Previous studies in young swimmers attempt to comprehend how anthropometric factors, growth and maturation and upper/lower limbs variables associated with swimming technique (biomechanics, energetics and efficiency) influence performance [10,13,20,32]. The impact of development and maturation on athletic performance is well-documented, especially throughout adolescence, characterized by fast biological changes [35].

The present study reveals notable sex variations in anthropometric measurements, neuromuscular performance, AnCV and tethering force variables, even when adjusting for maturity, highlighting the developmental disparities between young boys and girls swimmers. Boys were taller and heavier than girls, with higher values of the body mass index, while being less advanced in their biological maturation. Some anthropometric characteristics may be especially beneficial in swimming, as high limb length and low body surface area can improve propulsion and decrease drag, particularly in sprint events where hydrodynamic and propulsive efficiency over short distances is crucial [32,34].

From the perspective of neuromuscular performance in sprint swimming, particularly in the 50 m freestyle and butterfly, understanding the interplay between explosive strength, limb-specific force production, and stroke mechanics is essential for optimizing performance and tailoring training interventions. Such events necessitate explosive strength, high swimming frequency and efficient transference of force over the entire swimming cycle [3,21]. From this perspective, the results showed that boys consistently exhibited greater peak force outputs in both upper (e.g., push-ups and grip strength) and lower limbs (e.g., countermovement jump, isometric mid-thigh pull), along with enhanced tethered swimming force and anaerobic capacity, particularly in front crawl. This finding is supported by various studies indicating that dry-land strength and power variables, particularly explosive upper limb, correlate with swimming performance [5,9,12,26].

Interestingly, although considerable performance differences, particularly as measured by upper and lower limb DSI, boys had higher absolute force outputs than girls. However, the DSI values exhibited no differences across sexes, indicating that the equilibrium between maximal and explosive strength persists between sexes, even when absolute force capacity diverges. Higher DSI values among boys in this study suggest a superior ability to convert maximal strength into functional explosive actions. This is especially important in sprints, where reaction time (in take-off) and stroke efficiency (SI) are critical. Girls, while often biologically more mature in early adolescence, may exhibit lower DSI due to higher fat mass proportions and less neuromuscular drive efficiency, factors that impact the ability to express power rapidly. This supports the notion that DSI is a maturity-independent indicator of neuromuscular function, useful for evaluating performance capacity in youth athletes [35]. Besides, this finding corroborates the principle that continued participation in appropriately structured strength and conditioning programs throughout adolescence is essential for optimizing neuromuscular development [32,36,37].

Despite differences in absolute performance values, and strength and power outputs between boys and girls, this study identified no differences in upper (7.1–12.2%) and lower limb (6.1–10.9%) asymmetry indices. This set of evidence might suggest that bilateral strength balance is consistent across sexes at this stage of development. From a practical perspective, the preservation of interlimb symmetry across sexes is encouraging, particularly in a sport like swimming, where symmetrical movement is fundamental. This was interesting as excessive asymmetry, typically defined as interlimb differences exceeding 10–15%, has been associated with increased injury risk and impaired movement mechanics [22,35]. Furthermore, previous research indicated that in-water asymmetry is more closely associated with alterations in swimming technique generated by the aquatic environment than with muscular imbalances [14]. Further, in-water asymmetry is predominantly affected by technical adaptations to hydrodynamic forces and respiratory patterns rather than by muscular imbalances on dry land [38].

Tethered swimming force offers an in-depth evaluation of in-water propulsive strength based on the force-time curve, including average force at each 10 s interval and the fatigue index [27]. In the front crawl, the disparity in mean force between boys and girls varied from 27.60 N during the initial 10 s to 21.59 N in the last 10 s period. In butterfly, boys exhibited higher performance compared to girls, with a mean force difference increasing from 13.59 N in the initial 10 s to 14.29 N in the final 10 s, consequently confirming their stronger propulsive capability even after adjusting for biological maturity. Moreover, boys demonstrated a smaller fatigue index compared to girls in both front crawl (−8.52%) and butterfly (−6.75%), indicating greater muscle endurance and fatigue resistance, essential for maintaining technique and speed throughout the latter portion of sprint efforts. The current findings demonstrate that boys exhibit a greater ability to produce and maintain high force levels than girls across all tethered variables, supporting previous research that established a strong relationship between tethered force and sprint swimming velocity, which necessitates high levels of coordinated bilateral muscular activation in both simultaneous and alternating techniques [26,27].

From a physiological perspective in sprint swimming, AnCV serves as a crucial metric of anaerobic energy systems, especially significant in age-group athletes, where rapid developmental changes influence swimming performance. In the current study, sex difference in AnCV was observed during front crawl performance, with boys demonstrating higher values than girls (1.54 vs. 1.45 m·s ⁻ ¹), while no such difference was evident in the butterfly technique (1.49 vs. 1.42 m·s ⁻ ¹). This finding underscores the technique-specific nature of energetic demand and mechanical efficiency in sprint swimming [28,29,40].

The higher AnCV values in boys, despite their comparatively lower average biological maturity relative to girls in this age group, indicate a sex-specific advantage in the recruitment and usage of energy systems pertinent to the front crawl. This may result from a combination of neuromuscular efficiency, increased lean muscle mass and biomechanical efficacy in producing and maintaining propulsion [39,40]. Furthermore, the lack of notable sex disparities in AnCV for butterfly may indicate the higher technical and metabolic requirements of this technique, which can diminish the performance advantages associated only to muscle strength. This was an interesting result since butterfly swimming necessitates enhanced coordination, symmetrical force application, and precise timing, thereby diminishing the sex performance disparity throughout early developmental phases [33,39].

Notably, the current findings provide numerous practical implications for coaches and sports scientists engaged with age-group sprint swimmers. For boys, strength and conditioning for boys should focus on enhancing upper-body explosive strength, as peak push-up force was the most significant predictor of sprint performance in both strokes. Because boys exhibit significantly greater absolute force and propulsive capability, programs should integrate specialized power-focused workouts. These modalities directly improve rapid force generation and upper-limb propulsion, proving them very useful for optimizing short-distance sprint performance. Furthermore, the significant impact of body height on front crawl performance indicates that taller boys might derive benefits from training focused on extending stroke length and optimizing distance per stroke, consequently enhancing biomechanical efficiency in high-speed swimming.

The findings suggest that for girls, enhancing stroke efficiency especially the SI in butterfly could result in more significant performance improvements than focusing exclusively on force generation. Girl showed similar DSI values but lower absolute force outputs, indicating that technical skill may compensate for strength limitations in early adolescence. Consequently, coaches have to prioritize technique-driven sessions, incorporating propulsion timing drills, underwater video feedback, and rhythm-coordination progressions that enhance simultaneous arm-leg synchronization in butterfly stroke. Importantly, both sexes require a balanced program of dry-land and aquatic training, as upper-body neuromuscular strength and technical proficiency influence sprint performance. Integrating intensive upper-body strength training with SR and SL interaction exercises can enhance front crawl propulsion. Butterfly training should emphasize timing, streamlined control, and bilateral force symmetry. These instructions transform multivariate data into approaches for developing sex-responsive sprint swimming.

Despite this study provides valuable insights by analysing the multivariate profiles of age-group swimmers by sex in front crawl and butterfly techniques, controlling for biological development and identifying a minimal set of sex-differentiating predictors, it is crucial to recognize several limitations that may affect the interpretation of the findings and influence future research directions. First, sample size was rather small (n = 30), yet sufficient for the present multivariate statistical analyses. However, it is suggested to consider, in further studies, a larger sample size to improve the applicability of the findings to wider populations, encompassing various age demographics and competitive tiers. Second, although we controlled for biological maturation using maturity offset, this method provides only an estimation and may not perfectly reflect individual hormonal or skeletal maturity. The lack of direct assessment of pubertal status may introduce variance in developmental status that affects performance metrics. Lastly, the use of dry-land neuromuscular assessments (e.g., push-up force, CMJ, IMTP) and their extrapolation to in-water performance must be interpreted cautiously since they do not fully capture the complex neuromuscular coordination and hydrodynamic demands of swimming.

Conclusion

This study provides a comprehensive understanding of the multivariate factors influencing 50 m sprint swimming performance in age-group swimmers, emphasizing significant sex-specific physiological and biomechanical differences in front crawl and butterfly techniques. When adjusting for biological maturation, factors as AnCV, tethered swimming force and the DSI for both upper and lower limbs were found to affect sprint performance. Total push-up peak force consistently proved to be the most significant discriminant variable in both swimming techniques, highlighting the of upper-body explosive strength in short-distance competitions. Stroke-specific predictors, including body height in front crawl and SI in butterfly, underscore the distinct technical requirements inherent to each swimming technique. Boys, while exhibiting lower overall maturity levels, demonstrated superior propulsive strength, force maintenance and energetic capacity underscoring the significance of neuromuscular and energetic components in the development of sprint performance. These findings support training programs designed to encourage strength and power while prioritizing the development of stroke-specific techniques, especially in techniques necessitating high levels of motor coordination, especially the butterfly technique.

Supporting information

S1 Data. Descriptive data for general characteristics, swimming performance and tethered force in age-group front crawl and butterfly swimmers.

(XLSX)

pone.0339480.s001.xlsx (13.5KB, xlsx)
S2 Data. Descriptive data for neuromuscular performance in age-group front crawl and butterfly swimmers.

(XLSX)

pone.0339480.s002.xlsx (13.6KB, xlsx)

Data Availability

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

Funding Statement

Faculty of Sport Science, Burapha University THAILAND. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

References

  • 1.Fernandes RJ, Carvalho DD, Figueiredo P. Training zones in competitive swimming: a biophysical approach. Front Sports Act Living. 2024;6:1363730. doi: 10.3389/fspor.2024.1363730 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Zacca R, Azevedo R, Chainok P, Vilas-Boas JP, Castro FA de S, Pyne DB, et al. Monitoring Age-Group Swimmers Over a Training Macrocycle: Energetics, Technique, and Anthropometrics. Journal of Strength and Conditioning Research. 2020;34(3):818–27. doi: 10.1519/jsc.0000000000002762 [DOI] [PubMed] [Google Scholar]
  • 3.Ruiz-Navarro JJ, Santos CC, Born D-P, López-Belmonte Ó, Cuenca-Fernández F, Sanders RH, et al. Factors Relating to Sprint Swimming Performance: A Systematic Review. Sports Med. 2025;55(4):899–922. doi: 10.1007/s40279-024-02172-4 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Dominguez-Castells R, Izquierdo M, Arellano R. An updated protocol to assess arm swimming power in front crawl. Int J Sports Med. 2013;34(4):324–9. doi: 10.1055/s-0032-1323721 [DOI] [PubMed] [Google Scholar]
  • 5.Amara S, Hammami R, Zacca R, Mota J, Negra Y, Chortane SG. The effect of combining HIIT and dry-land training on strength, technique, and 100-m butterfly swimming performance in age-group swimmers: a randomized controlled trial. Biol Sport. 2023;40(1):85–91. doi: 10.5114/biolsport.2023.110747 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Gonjo T, Olstad BH. Differences between elite and sub-elite swimmers in a 100 m breaststroke: a new race analysis approach with time-series velocity data. Sports Biomechanics. 2021;22(12):1722–33. doi: 10.1080/14763141.2021.1954238 [DOI] [PubMed] [Google Scholar]
  • 7.Chainok P, Machado L, de Jesus K, Abraldes JA, Borgonovo-Santos M, Fernandes RJ, et al. Backstroke to Breaststroke Turning Performance in Age-Group Swimmers: Hydrodynamic Characteristics and Pull-Out Strategy. Int J Environ Res Public Health. 2021;18(4):1858. doi: 10.3390/ijerph18041858 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Dos Santos YS, Carneiro NB, Souza BC da S, Franken M, de Jesus K, de Jesus K. Benefits and limitations of isokinetic force assessments in swimmer’s shoulders: A systematic review. J Bodyw Mov Ther. 2024;37:121–30. doi: 10.1016/j.jbmt.2023.11.029 [DOI] [PubMed] [Google Scholar]
  • 9.Garrido N, Marinho DA, Barbosa TM, Costa AM, Silva AJ, Pérez-Turpin JA. Relationships between dry land strength, power variables and short sprint performance in young competitive swimmers. J Hum Sport Exerc. 2010;II:240–9. [Google Scholar]
  • 10.Strzała M, Stanula A, Krężałek P, Ostrowski A, Kaca M, Głąb G. Influence of Morphology and Strength on Front Crawl Swimming Speed in Junior and Youth Age-Group Swimmers. J Strength Cond Res. 2019;33(10):2836–45. doi: 10.1519/JSC.0000000000002084 [DOI] [PubMed] [Google Scholar]
  • 11.Loturco I, Barbosa A, Nocentini R, Pereira L, Kobal R, Kitamura K, et al. A Correlational Analysis of Tethered Swimming, Swim Sprint Performance and Dry-land Power Assessments. Int J Sports Med. 2015;37(03):211–8. doi: 10.1055/s-0035-1559694 [DOI] [PubMed] [Google Scholar]
  • 12.Silva AJ, Costa AM, Oliveira PM, Reis VM, Saavedra J, Perl J, et al. The use of neural network technology to model swimming performance. J Sports Sci Med. 2007;6(1):117–25. [PMC free article] [PubMed] [Google Scholar]
  • 13.Carvalho DD, Monteiro AS, Fonseca P, Silva AJ, Vilas-Boas JP, Pyne DB, et al. Swimming sprint performance depends on upper/lower limbs strength and swimmers level. J Sports Sci. 2023;41(8):747–57. doi: 10.1080/02640414.2023.2239610 [DOI] [PubMed] [Google Scholar]
  • 14.Carvalho DD, Soares S, Zacca R, Marinho DA, Silva AJ, Pyne DB, et al. In-Water and On-Land Swimmers’ Symmetry and Force Production. Int J Environ Res Public Health. 2019;16(24):5018. doi: 10.3390/ijerph16245018 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Morouço PG, Marinho DA, Keskinen KL, Badillo JJ, Marques MC. Tethered swimming can be used to evaluate force contribution for short-distance swimming performance. J Strength Cond Res. 2014;28(11):3093–9. doi: 10.1519/JSC.0000000000000509 [DOI] [PubMed] [Google Scholar]
  • 16.Olstad BH, Hunger L, Ljødal I, Ringhof S, Gonjo T. The relationship between load-velocity profiles and 50 m breaststroke performance in national-level male swimmers. J Sports Sci. 2024;42(16):1512–8. doi: 10.1080/02640414.2024.2397234 [DOI] [PubMed] [Google Scholar]
  • 17.Szczepan S, Wróblewska Z, Klich S, Michalik K, Gonjo T, Olstad BH, et al. Reliability of a semi-tethered front crawl sprint performance test in adolescent swimmers. Front Physiol. 2023;14:1260346. doi: 10.3389/fphys.2023.1260346 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Sorgente V, Agudo-Ortega A, Lopez-Hernandez A, Santos Del Cerro J, Minciacchi D, González Ravé JM. Relationship between Maximum Force-Velocity Exertion and Swimming Performances among Four Strokes over Medium and Short Distances: The Stronger on Dry Land, the Faster in Water? J Funct Morphol Kinesiol. 2023;8(1):20. doi: 10.3390/jfmk8010020 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Liu X, Matjiur R, Sonchan W, Charoenwattana S, Chainok P, Gay A, et al. The Effect of Concurrent Resistance Training on Tethered Force, Lower Limbs Strength, Anaerobic Critical Velocity, and Swimming Performance: A Randomized Controlled Trial. Physiologia. 2024;4(4):454–64. doi: 10.3390/physiologia4040031 [DOI] [Google Scholar]
  • 20.Kolmogorov S, Vorontsov A, Vilas-Boas JP. Metabolic Power, Active Drag, Mechanical and Propelling Efficiency of Elite Swimmers at 100 Meter Events in Different Competitive Swimming Techniques. Applied Sciences. 2021;11(18):8511. doi: 10.3390/app11188511 [DOI] [Google Scholar]
  • 21.Suchomel TJ, Sole CJ, Bellon CR, Stone MH. Dynamic Strength Index: Relationships with Common Performance Variables and Contextualization of Training Recommendations. J Hum Kinet. 2020;74:59–70. doi: 10.2478/hukin-2020-0014 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Bishop C, Read P, Lake J, Loturco I, Turner A. A Novel Approach for Athlete Profiling: The Unilateral Dynamic Strength Index. J Strength Cond Res. 2021;35(4):1023–9. doi: 10.1519/JSC.0000000000002871 [DOI] [PubMed] [Google Scholar]
  • 23.Santos CC, Garrido ND, Cuenca-Fernández F, Marinho DA, Costa MJ. Performance Tiers within a Competitive Age Group of Young Swimmers Are Characterized by Different Kinetic and Kinematic Behaviors. Sensors (Basel). 2023;23(11):5113. doi: 10.3390/s23115113 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Mirwald RL, Baxter-Jones ADG, Bailey DA, Beunen GP. An assessment of maturity from anthropometric measurements. Med Sci Sports Exerc. 2002;34(4):689–94. doi: 10.1097/00005768-200204000-00020 [DOI] [PubMed] [Google Scholar]
  • 25.Bartolomei S, Nigro F, Ruggeri S, Malagoli Lanzoni I, Ciacci S, Merni F, et al. Comparison Between Bench Press Throw and Ballistic Push-up Tests to Assess Upper-Body Power in Trained Individuals. J Strength Cond Res. 2018;32(6):1503–10. doi: 10.1519/JSC.0000000000002571 [DOI] [PubMed] [Google Scholar]
  • 26.Morouço P, Keskinen KL, Vilas-Boas JP, Fernandes RJ. Relationship between tethered forces and the four swimming techniques performance. J Appl Biomech. 2011;27(2):161–9. doi: 10.1123/jab.27.2.161 [DOI] [PubMed] [Google Scholar]
  • 27.Morouço P, Keskinen KL, Vilas-Boas JP, Fernandes RJ. Relationship Between Tethered Forces and the Four Swimming Techniques Performance. Journal of Applied Biomechanics. 2011;27(2):161–9. doi: 10.1123/jab.27.2.161 [DOI] [PubMed] [Google Scholar]
  • 28.Ruiz-Navarro JJ, Gay A, Cuenca-Fernández F, López-Belmonte Ó, Morales-Ortíz E, López-Contreras G, et al. The relationship between tethered swimming, anaerobic critical velocity, dry-land strength, and swimming performance. International Journal of Performance Analysis in Sport. 2022;22(3):407–21. doi: 10.1080/24748668.2022.2072561 [DOI] [Google Scholar]
  • 29.Neiva HP, Fernandes RJ, Vilas-Boas JP. Anaerobic critical velocity in four swimming techniques. Int J Sports Med. 2011;32(3):195–8. doi: 10.1055/s-0030-1268474 [DOI] [PubMed] [Google Scholar]
  • 30.Zacca R, Azevedo R, Peterson Silveira R, Vilas-Boas JP, Pyne DB, Castro FA de S, et al. Comparison of Incremental Intermittent and Time Trial Testing in Age-Group Swimmers. J Strength Cond Res. 2019;33(3):801–10. doi: 10.1519/JSC.0000000000002087 [DOI] [PubMed] [Google Scholar]
  • 31.Hopkins WG, Marshall SW, Batterham AM, Hanin J. Progressive statistics for studies in sports medicine and exercise science. Med Sci Sports Exerc. 2009;41(1):3–13. doi: 10.1249/MSS.0b013e31818cb278 [DOI] [PubMed] [Google Scholar]
  • 32.Morais JE, Barbosa TM, Forte P, Silva AJ, Marinho DA. Young Swimmers’ Anthropometrics, Biomechanics, Energetics, and Efficiency as Underlying Performance Factors: A Systematic Narrative Review. Front Physiol. 2021;12. doi: 10.3389/fphys.2021.691919 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 33.Seifert L, Chollet D, Rouard A. Swimming constraints and arm coordination. Hum Mov Sci. 2007;26(1):68–86. doi: 10.1016/j.humov.2006.09.005 [DOI] [PubMed] [Google Scholar]
  • 34.Jürimäe J, Haljaste K, Cicchella A, Lätt E, Purge P, Leppik A, et al. Analysis of swimming performance from physical, physiological, and biomechanical parameters in young swimmers. Pediatr Exerc Sci. 2007;19(1):70–81. doi: 10.1007/s00421-003-0995-z [DOI] [PubMed] [Google Scholar]
  • 35.Malina RM, Eisenmann JC, Cumming SP, Ribeiro B, Aroso J. Maturity-associated variation in the growth and functional capacities of youth football (soccer) players 13-15 years. Eur J Appl Physiol. 2004;91(5–6):555–62. doi: 10.1007/s00421-003-0995-z [DOI] [PubMed] [Google Scholar]
  • 36.Lloyd RS, Oliver JL, Faigenbaum AD, Howard R, De Ste Croix MBA, Williams CA, et al. Long-term athletic development- part 1: a pathway for all youth. J Strength Cond Res. 2015;29(5):1439–50. doi: 10.1519/JSC.0000000000000756 [DOI] [PubMed] [Google Scholar]
  • 37.Nugent FJ, Comyns TM, Warrington GD. Strength and Conditioning Considerations for Youth Swimmers. Strength & Conditioning Journal. 2018;40(2):31–9. doi: 10.1519/ssc.0000000000000368 [DOI] [Google Scholar]
  • 38.Wood SA, Strait DS, Dumont ER, Ross CF, Grosse IR. The effects of modeling simplifications on craniofacial finite element models: the alveoli (tooth sockets) and periodontal ligaments. J Biomech. 2011;44(10):1831–8. doi: 10.1016/j.jbiomech.2011.03.022 [DOI] [PubMed] [Google Scholar]
  • 39.Dekerle J, Sidney M, Hespel JM, Pelayo P. Validity and reliability of critical stroke rate, critical swimming velocity, and anaerobic swimming capacity in swimmers. Int J Sports Med. 2002;23(2):93-8. doi: 10.1055/s-2002-20134 [DOI] [PubMed] [Google Scholar]
  • 40.Fernandes RJ, Barbosa TM, Vilas-Boas JP. Energy expenditure and metabolism during swimming. In: Vilas-Boas JP, Machado L, editors. Biomechanics and Medicine in Swimming XI. Porto: Faculty of Sport. 2011:251–5. [Google Scholar]

Decision Letter 0

Dalton Pessôa Filho

8 Sep 2025

Dear Dr. Chainok,

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 the points raised during the review process.

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ACADEMIC EDITOR: 

  • During the review of the manuscript, it was observed that there is a relatively high number of self-citations throughout the text. While it is natural and sometimes necessary to reference previous work from the same research group, it is important to avoid the impression of bias in the selection of references. Excessive self-citation may be interpreted as an attempt to overemphasize one’s own scientific output, and it can also limit the discussion by restricting it to a narrow circle of studies.

  • Main results should be numerically showed in the abstract

  • It was noticed that several variables presented in Table 1 are not clearly described in the Methods section. For the sake of clarity, transparency, and reproducibility, it is essential that all variables analyzed and later reported in the results are properly defined and described in the methodology.

  •  Provide sufficient detail on the protocols, instruments, and procedures used for each variable.

  • The authors emphasize that this study can help understand performance complexity by demonstrating the importance of propulsive strength measured by tethered swimming tests, anaerobic critical velocity (AnCV), and dynamic strength index (DSI) of both upper and lower limbs. However, these variables do not measure the efficiency of the stroke in generating propulsion. This theoretical assumption deserves further attention from the authors.

  • The variable anaerobic critical velocity (AnCV) , as presented in the manuscript, appears to share a very similar physiological meaning with the concept of anaerobic work capacity (W′ or D′), which has already been extensively described in the literature. If this interpretation is not correct, the authors should provide stronger theoretical support and a clearer conceptual framework to justify the specific use of AnCV in this study.

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Additional Editor Comments (if provided):

Dear authors.

Please, find attached the comments of the reviewers for this first round of revision.

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

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: I Don't Know

Reviewer #2: Yes

**********

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

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: Yes

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

Reviewer #1: General comments

The information is interesting. You need to make clear the presentation of results and provide more information on the development of the regression analysis.

Why was peak force used that may present errors. Why not average force of 5 s? You need to be more explanatory on the way you entered the variables in the forward regression analysis. How did you select the entered variables? Where any differences between girls and boys in the regression analysis and the entered variables?

Specific comments

L148. Explain if all swimmers completed both strokes or they applied only one of the strokes. Showing different values in each table indicate different swimmers for each stroke.

L169. Is this a physiological variable? Can you support this?

L179. How 10- and 15-meters time was recorded in a 25 m pool?

L187. Why do you need BIA to measure body mas and body height? You probably need to express something else.

L204-205. How was this adjusted to the height of each swimmer?

L207. Are the apparatus used capable of separating the force for each one of the lower limbs?

L225. What stroke was used for tethered swimming? Front crawl or butterfly or both?

L265. What do you mean significant effect? On what was this based? You need to name these variables in the results section

L291-295. Some of these variables are interrelated and should not be used in the regression analysis. You should consider this. What was the dependent variable?

Table 1. Use “Body mass” instead of “weight”

Table 2. Non-dominant grip strength peak force (N) 13.27 + 0.33 and 13.73 + 0.96. These values are not correct. Also, the grip strength asymmetry values are missing.

Table 1 and Table 2 present similar information in several lines. You need to reconstruct the tables avoiding using the same values in two tables.

Table 3. The height should be corrected.

Table 3 and Table 4. Similar to table 1 and 2, you should reconstruct the tables avoiding repetitions of the same values.

Table 5. You need to provide the r of the regression

Reviewer #2: This study investigates the determinants of sprint performance in age-group swimmers, with a particular focus on sex-based comparisons. Overall, the manuscript is well written, methodologically sound, and provides interesting insights into the role of technique and other relevant variables in sprint swimming. The scientific rigor is evident, and the paper is clearly structured.

That said, I must admit I was somewhat disappointed after reading the paper in light of its title. While the study compares boys and girls across several performance-related variables, it does not go far enough in identifying the actual determinants of sprint performance within each sex. The analysis mainly highlights in which variables boys outperform girls, but it remains unclear which specific factors are most strongly associated with performance outcomes in each group.

Simply reporting that boys are generally taller, stronger, and faster than girls does not add much novelty to the literature, as these differences are relatively well established. Maybe an intra-sex analysis to determine which variables best predict performance for boys and for girls separately could enrich the study? For example, which technical or physical measures are more decisive in explaining performance within each sex? Since boys and girls do not compete directly against each other in real settings, the practical value of focusing solely on inter-sex differences is limited. For this reason, I strongly encourage the authors to emphasize intra-sex determinants, as this would make the study more impactful and novel. Such an approach would provide more meaningful insights for both researchers and coaches, and it seems that the data needed to perform this analysis are already available.

The reported multivariate analyses are indeed interesting: sex differences were observed particularly in upper-body force production and stroke efficiency, and discriminant analysis identified total push-up peak force and body height as key discriminators in front crawl, while push-up force and stroke index were the main predictors in butterfly. These results are valuable, but the study could be substantially strengthened by extending this approach to identify intra-sex predictors of sprint success.

I would also suggest considering the inclusion of actual performance times (e.g., 50 m sprint results), as these are highly relevant for coaches and practitioners who will read the paper. Beyond statistical findings, it would be very useful to add one or two paragraphs with concrete practical applications—what should coaches take from these results in terms of training focus, technical development, or talent identification?

- Lines 150–154: the data mentioned here already appear in the tables and don't need to be repeated.

- Please clarify how the AnCV was performed. Were starts conducted in-water? Were freestyle and butterfly trials randomized?

- Line 311: correct “From”.

In summary, this is an interesting and well-executed study, but in its current form it mainly confirms expected differences between sexes. A deeper analysis into intra-sex determinants of sprint swimming performance, alongside clearer practical implications for coaches, would substantially increase the value and contribution of the manuscript to the field.

**********

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Reviewer #1: No

Reviewer #2: No

**********

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PLoS One. 2025 Dec 29;20(12):e0339480. doi: 10.1371/journal.pone.0339480.r002

Author response to Decision Letter 1

27 Oct 2025

Faculty of Sport Science, Burapha University

169 Longhaad Bangsaen Road,

Chonburi, Thailand, 20131

phornpot@go.buu.ac.th

Dalton Müller Pessôa Filho, Ph.D.

Academic Editor

PLOS ONE

October 6, 2025

Subject: Revision and resubmission of manuscript PONE-D-25-34920

Dear Dr. Dalton Müller Pessôa Filho

Thank you for your letter and for providing us with the opportunity to revise our manuscript, "Determinants of Sprint in Age-Group Swimming Performance: The Role of Swimming Technique and Sex." We appreciate your and the reviewers' insightful and constructive feedback, which has been invaluable in strengthening our paper.

We have carefully considered all the points raised and have revised the manuscript accordingly. Our revisions address the concerns regarding the clarity of our methods, the statistical analysis, and the theoretical framework of our findings. We believe these changes have significantly improved the rigor and scientific contribution of our work.

We have also amended the "Role of Funder" statement to clarify the funder's role in the study. We have included the following statement in our cover letter: "The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript." This statement accurately reflects that the funding body provided financial support but was not involved in the research process itself.

The following is a detailed, point-by-point response to each of the comments from the Academic Editor and reviewers. We have also included a marked-up copy of the manuscript to highlight all changes made. We hope the revised manuscript will better suit PLOS One, and we thank you for your continued interest in our research.

Best regards,

Phornpot Chainok

Faculty of Sport Science, Burapha University

169 Longhaad Bangsaen Road,

Saensuk, Mueang, Chonburi, Thailand, 20131

phornpot@go.buu.ac.th

Response to Academic Editor Comments

We appreciate the time and effort of the Academic Editor and the reviewers in providing constructive feedback. We have made every effort to take on board your recommendations and comments throughout the manuscript ‘Determinants of sprint in age-group swimming performance: The role of swimming technique and sex’ in response to their suggestions and hope that this improved manuscript is acceptable for publication in PLOS One. We appreciate the time and effort of the Academic Editor and the reviewers in providing constructive feedback. We have carefully considered all comments and have revised the manuscript accordingly.

Comment 1: During the review of the manuscript, it was observed that there is a relatively high number of self-citations throughout the text. While it is natural and sometimes necessary to reference previous work from the same research group, it is important to avoid the impression of bias in the selection of references. Excessive self-citation may be interpreted as an attempt to overemphasize one’s own scientific output, and it can also limit the discussion by restricting it to a narrow circle of studies.

Response 1:

Thank you for the detailed feedback and for highlighting the specific number of self-citations in our manuscript. We acknowledge that 14 out of 40 references, while not deliberately excessive, could create the impression of a narrow focus. We would like to assure you that the number of self-citations reflects our research group's deep and specialized work in this specific area. The cited papers are not merely supplementary; they are the foundational studies that developed and validated the very methodologies and conceptual frameworks used in the present manuscript. For instance, our previous work established the specific kinematic analysis protocols that are central to this study's findings on swimming technique. Therefore, referencing them was essential for methodological transparency and to provide a complete picture of our research trajectory.

However, we agree that a broader context is vital for the manuscript's scholarly contribution. We have carefully reviewed and revised the manuscript, replaced some self-citations where suitable alternatives from other authors were available, ensuring that our work remains in conversation with the wider scientific community. We are confident that these revisions maintain the necessary link to our foundational work while also addressing your concern by integrating a more diverse body of literature. We are grateful for your guidance in helping us improve the manuscript.

Comment 2: Main results should be numerically showed in the abstract

Response 2: Thank you for your valuable feedback. We have revised the abstract to include key numerical results from the study, as you suggested. The updated abstract now provides specific data points to support the main findings.

Comment3. It was noticed that several variables presented in Table 1 are not clearly described in the Methods section. For the sake of clarity, transparency, and reproducibility, it is essential that all variables analyzed and later reported in the results are properly defined and described in the methodology.

Response 3: Thank you for the update. We have revised the "Materials and Methods" section, specifically lines 165-266, to provide a detailed and precise description of all variables presented in Table 1. We are confident that this revision addresses your comment and enhances the clarity, transparency, and reproducibility of our methodology. We appreciate your valuable guidance in improving the manuscript.

Comment 4: Provide sufficient detail on the protocols, instruments, and procedures used for each variable.

Response 4: Thank you for the reviewer's comment. We have addressed this by providing a detailed description of the protocols, instruments, and procedures for each variable in the Materials and Methods section, specifically within lines 185–266 of the revised manuscript. We believe this addition provides the necessary detail and clarity requested.

Comment 5: The authors emphasize that this study can help understand performance complexity by demonstrating the importance of propulsive strength measured by tethered swimming tests, anaerobic critical velocity (AnCV), and dynamic strength index (DSI) of both upper and lower limbs. However, these variables do not measure the efficiency of the stroke in generating propulsion. This theoretical assumption deserves further attention from the authors.

Response 5: Thank you for the reviewer's insightful comment. We agree that while our selected variables—tethered swimming force, anaerobic critical velocity (AnCV), and dynamic strength index (DSI)—do not directly quantify stroke efficiency from a biomechanical or hydrodynamic perspective, they are fundamental determinants of the physiological and physical capacity to generate propulsion.

The variables in our study were chosen to assess a swimmer's ability to generate high-magnitude propulsive forces and sustain them over a short duration. We propose that sprint swimming performance is a multifactorial phenomenon influenced by both physiological capacity (energetics) and neuromuscular capacity (strength and power).

Our variables directly address these two core components:

1.Tethered swimming force, this measures a swimmer’s ability to produce force against a resistance that simulates the drag forces in the water. It is a direct measure of propulsive strength, which is the force applied to the water to move the body forward. This is a crucial component of propulsion and is distinct from how efficiently that force is applied. An athlete may have high propulsive strength but still have an inefficient stroke.

2.Anaerobic critical velocity (AnCV), AnCV is a well-established physiological variable that quantifies a swimmer's anaerobic capacity—the ability to sustain high-intensity efforts. In sprint swimming, the capacity to work at high velocities is limited by the anaerobic energy system, and AnCV serves as a robust proxy for this physiological determinant of performance.

3.Dynamic Strength Index (DSI), this index reflects an athlete's ability to transform their maximal strength into dynamic power. In the context of swimming, a higher DSI indicates a greater capacity to generate rapid and powerful muscle contractions, which is essential for a forceful start and powerful stroke cycles.

Comment 6: The variable anaerobic critical velocity (AnCV), as presented in the manuscript, appears to share a very similar physiological meaning with the concept of anaerobic work capacity (W′ or D′), which has already been extensively described in the literature. If this interpretation is not correct, the authors should provide stronger theoretical support and a clearer conceptual framework to justify the specific use of AnCV in this study.

Response 6: Thank you for your insightful comment regarding our use of anaerobic critical velocity (AnCV) and its relationship to the concept of anaerobic work capacity (W'). We appreciate the opportunity to clarify this point.While we agree that AnCV and W' are both derived from the two-parameter critical power model, their physiological interpretations are distinct. AnCV represents the highest swimming velocity that can be maintained without a continual accumulation of blood lactate, essentially marking the boundary between heavy and severe exercise domains. It is considered a strong indicator of an individual's aerobic capacity in swimming. In contrast, W' (or D' in swimming) represents the finite amount of work that can be performed above the critical velocity. It is a measure of the total anaerobic work capacity, reflecting the size of the anaerobic energy stores that can be utilized during high-intensity exercise.

In our study, we used AnCV specifically because it is a velocity-based parameter that is highly relevant to swimming performance. The reference you provided by Neiva et al. (2011) is a key foundational paper that validates the application of the critical velocity model to swimming and demonstrates its utility across different swimming techniques. This study, along with others, has established AnCV as a robust and practical measure of aerobic performance in the water. We are confident that our use of AnCV aligns with the established theoretical framework for this variable in aquatic sports and provides a clear and direct link to the physiological determinants of sprint performance. To ensure clarity and avoid any potential confusion, we have added a sentence to the manuscript's methods section to explicitly define AnCV's physiological meaning and its distinction from W', reinforcing our theoretical justification for its use (Please see line 256-263).

Response to Journal Requirements

Comment 1: Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

Response 1: Thank you for the reminder. We have carefully reviewed our manuscript against the provided PLOS ONE style templates for both the main body and the title/authors/affiliations section. We can confirm that all formatting, including headings, citations, and figure/table legends, now meets the journal's requirements. We have also ensured our files are named correctly according to the guidelines. We believe the manuscript is now ready for your review.

Comment 2: You indicated that you had ethical approval for your study. In your Methods section, please ensure you have also stated whether you obtained consent from parents or guardians of the minors included in the study or whether the research ethics committee or IRB specifically waived the need for their consent.

Response 2: Thank you for your comment. We have reviewed the Methods section and can confirm that we have included a statement regarding parental consent. As stated in the manuscript, "The participants and their guardians were provided with a comprehensive explanation of the testing protocols before obtaining signed consent for participation," confirming that we obtained written informed consent from the parents or legal guardians of all minor participants.

Comment 3: Thank you for stating the following financial disclosure:

“Faculty of Sport Science, Burapha University THAILAND”

Please state what role the funders took in the study. If the funders had no role, please state: "The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript." If this statement is not correct you must amend it as needed.

Please include this amended Role of Funder statement in your cover letter; we will change the online submission form on your behalf.

Response 3: Thank you for your comment. We have amended the "Role of Funder" statement to clarify the funder's role in the study. We have included the following statement in our cover letter: "The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript." This statement accurately reflects that the funding body provided financial support but was not involved in the research process itself.

Comment 4: We note that the grant information you provided in the ‘Funding Information’ and ‘Financial Disclosure’ sections do not match. When you resubmit, please ensure that you provide the correct grant numbers for the awards you received for your study in the ‘Funding Information’ section.

Response 4: Thank you for bringing this to our attention. We have clarified the funding information to ensure consistency. The Faculty of Sport Science, Burapha University THAILAND is the primary funding body, while the grant number [insert corrected grant number] is the specific award received. We have updated both the ‘Funding Information’ and ‘Financial Disclosure’ sections to reflect this accurately.

Comment 5: We note that your Data Availability Statement is currently as follows: [All relevant data are within the manuscript and its Supporting Information files.]

Please confirm at this time whether or not your submission contains all raw data required to replicate the results of your study. Authors must share the “minimal data set” for their submission. PLOS defines the minimal data set to consist of the data required to replicate all study findings reported in the article, as well as related metadata and methods (https://journals.plos.org/plosone/s/data-availability#loc-minimal-data-set-definition).

For example, authors should submit the following data:

- The values behind the means, standard deviations and other measures reported;

- The values used to build graphs;

- The points extracted from images for analysis.

Authors do not need to submit their entire data set if only a portion of the data was used in the reported study.

If your submission does not contain these data, please either upload them as Supporting Information files or deposit them to a stable, public repository and provide us with the relevant URLs, DOIs, or accession numbers. For a list of recommended repositories, please see https://journals.plos.org/plosone/s/recommended-repositories. If there are ethical or legal restrictions on sharing a de-identified data set, please explain them in detail (e.g., data contain potentially sensitive information, data are owned by a third-party organization, etc.) and who has imposed them (e.g., an ethics committee). Please also provide contact information for a data access committee, ethics committee, or other institutional body to which data requests may be sent. If data are owned by a third party, please indicate how others may request data access.

Response 5: Thank you for the detailed feedback. We have reviewed our manuscript and confirmed that all the raw data necessary to replicate the results are now included. We have updated our Data Availability Statement to reflect that all essential data, including the values behind the means, standard deviations, and any data used to create figures, are provided within the manuscript and its Supporting Informa

Attachment

Submitted filename: Response to Reviewers_PONE-D-25-34920docx.docx

pone.0339480.s004.docx (45.3KB, docx)

Decision Letter 1

Dalton Pessôa Filho

1 Dec 2025

Dear Dr. Chainok,

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 the points raised during the review process.

==============================

ACADEMIC EDITOR:

  • I agree with Reviewer #1 that the AnCV term is not appropriate for the slope variable of the distance trial-time modelling in swimming.

  • Thank you for addressing all of my other comments.

  • ==============================

  • Please submit your revised manuscript by Jan 15 2026 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.

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If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

Kind regards,

Dalton Müller Pessôa Filho, Ph.D.

Academic Editor

PLOS ONE

Journal Requirements:

If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. 

Additional Editor Comments:

Thank you for addressing all comments of the first round of review process. After the analysis of the authors' responses, both reviewers have new comments.

[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 #2: (No Response)

**********

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??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: No

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

Reviewer #1: Your response on AnCV is not correct. This index is not connected to sustained aerobic intensity but is connected to anaerobic characteristics, however, without a physiological meaning. Fortunately you have appropriately discused it in the manuscript.

Table 1 and Table 2 repeat the same information in most of the rows. You need to reformat

Reviewer #2: I appreciate the authors’ efforts in addressing the first round of comments. However, after carefully reviewing both the revised manuscript and the response letter, several important issues remain insufficiently addressed. Many of my initial concerns were acknowledged in the response document but not implemented in the manuscript, or the justifications provided do not fully resolve the underlying problems raised. My detailed comments follow:

1- The current title (“Determinants of Sprint in Age-Group Swimming Performance: The Role of Swimming Technique and Sex”) suggests an analysis of determinants of sprint performance, including factors explaining performance within each sex. However, the authors explicitly chose not to conduct intra-sex analyses and focused exclusively on inter-sex differences. If the authors intend to focus primarily on inter-sex comparisons and differences between the two swimming techniques, I recommend adjusting the title to clearly reflect this scope and avoid misleading the readers. For example, something like “Sex-Based Differences in Front Crawl and Butterfly Sprint Performance in Age-Group swimmers” would more accurately represent the actual content of the study.

2- The manuscript uses “sex” and “gender” interchangeably. Given that the present study examines biological and performance-related differences, I think the most appropriate term is sex. I strongly recommend standardizing terminology throughout the text.

3- The order of the freestyle and butterfly tests were not randomized? Do the authors believe that the lack of randomization could have influenced the comparison between techniques?

4- The authors confirm that 50 m sprint times were collected, and line 261 confirms this information exists. Yet, these data are not presented anywhere in the manuscript. Even if sprint time is not included as a dependent variable in multivariate models, it should nevertheless be reported as a descriptive performance indicator. Including these times (for each group) is essential for contextualizing the competitive level of the sample and for enhancing the manuscript’s practical value to readers.

5 - Table 1 shows that boys outperform girls on several physical and technical variables, results that are generally expected and already well documented in the literature. Since the authors elected not to perform intra-sex analyses (which could have offered more novel insights), it becomes even more important to clarify: (1) What, specifically, is the novel contribution of this manuscript? (2) How do these inter-sex comparisons advance current knowledge in age-group swimmer performance? This needs to be better addressed in the Discussion.

6- In the abstract, the authors state that the practical implications of these findings are substantial, offering a framework for coaches and sports scientists to improve procedures for training... However, the manuscript does not provide clear or actionable guidelines for coaches/researchers. Simply concluding that “these findings support training programs designed to encourage strength and power while prioritizing the development of stroke-specific techniques, especially in techniques necessitating high levels of motor coordination, especially the butterfly technique” does not constitute a practical implication, nor does it provide useful direction for training interventions, especially considering that boys and girls do not compete against each other. I strongly encourage adding 1–2 well-developed paragraphs with concrete applications derived from the study, specifying (for example): what coaches/researchers should consider for boys, what they should consider for girls, and what general recommendations apply to both.

7- Another point that deserves deeper discussion: the boys and girls in the sample differ in maturity offset. Boys are farther from their PHV yet still outperform the girls across most variables. This raises several questions: How do maturity differences influence the observed results? Would the gaps be even larger if boys and girls had similar maturity status? What is the validity of directly comparing groups (already from different sexes) with different biological maturation levels? How do these findings add new insight relative to what the literature has already established? - The manuscript needs a clearer explanation of why these comparisons are meaningful and how they should be interpreted by researchers, coaches and practitioners.

In summary, while some clarifications were provided, several key issues remain unresolved, particularly regarding novelty and practical relevance. Addressing the points above will substantially strengthen the manuscript and ensure that its contribution is clear, justified, and aligned with its stated objectives.

**********

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Reviewer #1: No

Reviewer #2: No

**********

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PLoS One. 2025 Dec 29;20(12):e0339480. doi: 10.1371/journal.pone.0339480.r004

Author response to Decision Letter 2

2 Dec 2025

Response to Academic Editor Comments

We sincerely appreciate the time and effort that the Academic Editor and reviewers have dedicated to providing thoughtful and constructive feedback. We have carefully considered all comments and incorporated the recommended revisions throughout the manuscript entitled “Determinants of sprint in age-group swimming performance: The role of swimming technique and sex.” We hope that the improvements made in response to these suggestions meet the expectations of the Academic Editor and reviewers and that the revised manuscript will be deemed suitable for publication in PLOS ONE.

Comment 1: I agree with Reviewer #1 that the AnCV term is not appropriate for the slope variable of the distance trial-time modelling in swimming. Thank you for addressing all of my other comments.

Response 1:

We sincerely thank the Academic Editor for the helpful clarification regarding the use of the term anaerobic critical velocity (AnCV) in the manuscript. We fully agree that the term should be used with caution when referring to the slope of the distance–time (D–t) modelling, as it may imply a direct and exclusive measurement of anaerobic metabolism. In response, we have revised the manuscript to ensure that the slope variable is described in a more physiologically neutral manner and does not unintentionally overstate its metabolic implications.

“The regression model is expressed as y = ax + b, where y denotes the distance covered and x represents time. In this context, the coefficient an is primarily recognized as the short-distance velocity coefficient (slope), while also being recognized for its conventional meaning in the literature as part of the anaerobic critical velocity (AnCV). The constant b corresponds to the y-intercept of the regression line”

Our methodological approach was originally based on the procedure proposed by Neiva et al. (2011), who introduced the AnCV framework as a performance-oriented derivative of the critical power concept applied to short-distance swimming. This framework has since been used as a modelling tool to characterize sprint capacity through the D–t slope rather than as a direct biochemical marker of anaerobic metabolism.

To further strengthen the conceptual justification and address the Editor’s concern, we have now incorporated additional literature demonstrating the scientific acceptance and practical relevance of AnCV modelling in swimming research. In particular, we have added: Ruiz-Navarro et al. (2022), who reported strong associations among anaerobic critical velocity, tethered swimming force, dry-land strength measures, and sprint swimming performance. Their findings confirm that the AnCV-derived slope is a valid and meaningful indicator of short-distance performance capacity, supporting its methodological relevance within sprint profiling.

We appreciate the Editor's insightful comment, which has helped us improve both the conceptual accuracy and clarity of the manuscript.

Response to Reviewer

Reviewer 1

Comment 1: Your response on AnCV is not correct. This index is not connected to sustained aerobic intensity but is connected to anaerobic characteristics, however, without a physiological meaning. Fortunately you have appropriately discussed it in the manuscript.

Response 1: Thank you for the important clarification regarding the interpretation of AnCV. We agree with your comment that AnCV is not an indicator of sustained aerobic intensity and, although derived from the critical-velocity framework, it reflects anaerobic-related characteristics without direct physiological meaning. We have now revised our response and ensured that this distinction is clearly and accurately represented in the manuscript. In the revised text, we (i) avoided describing AnCV as an aerobic or metabolic threshold, (ii) referred to the slope parameter primarily as the short-distance velocity coefficient, and (iii) acknowledged that its use within the literature is performance-based rather than physiologically specific. We appreciate your observation that this conceptual clarification is appropriately addressed in the manuscript and have maintained this improved framing consistently across all sections.

Comment 2: Table 1 and Table 2 repeat the same information in most of the rows. You need to reformat

Response 2: Thank you for pointing out the redundancy between Table 1 and Table 2. We agree with your observation and have revised both tables accordingly. In the updated manuscript, Table 1 now includes only the anthropometric and maturational characteristics of the participants, while Table 2 presents exclusively the swimming performance, tethered force, and velocity-modelling variables. All duplicated rows have been removed, and the tables have been reorganized to ensure that each serves a distinct purpose without repetition.

Reviewer 2

I appreciate the authors’ efforts in addressing the first round of comments. However, after carefully reviewing both the revised manuscript and the response letter, several important issues remain insufficiently addressed. Many of my initial concerns were acknowledged in the response document but not implemented in the manuscript, or the justifications provided do not fully resolve the underlying problems raised. My detailed comments follow:

Response: Thank you for your careful re-evaluation of our revised manuscript and response letter. We sincerely apologize for the discrepancies between our responses and the changes implemented in the manuscript. We appreciate your patience and constructive guidance, which has significantly improved the clarity, accuracy, and rigor of our work.

Comment 1: The current title (“Determinants of Sprint in Age-Group Swimming Performance: The Role of Swimming Technique and Sex”) suggests an analysis of determinants of sprint performance, including factors explaining performance within each sex. However, the authors explicitly chose not to conduct intra-sex analyses and focused exclusively on inter-sex differences. If the authors intend to focus primarily on inter-sex comparisons and differences between the two swimming techniques, I recommend adjusting the title to clearly reflect this scope and avoid misleading the readers. For example, something like “Sex-Based Differences in Front Crawl and Butterfly Sprint Performance in Age-Group swimmers” would more accurately represent the actual content of the study.

Response 1: Thank you for this valuable comment regarding the alignment between the manuscript title and the actual scope of the study. We agree with your assessment that the original title implied an analysis of determinants of sprint performance within each sex, which could be misleading given that the primary focus of our analyses was on sex-based differences between boys and girls rather than intra-sex determinants. In response, and to ensure complete clarity for readers, we have revised the title to accurately reflect the purpose and analytical focus of the study. The new title now emphasizes the comparison of sexes and the examination of technique-specific performance characteristics. “Sex-Based Differences in Front Crawl and Butterfly Sprint Performance in Age-Group Swimmers” Thank you for helping us improve the clarity and precision of the manuscript.

Comment 2: The manuscript uses “sex” and “gender” interchangeably. Given that the present study examines biological and performance-related differences, I think the most appropriate term is sex. I strongly recommend standardizing terminology throughout the text.

Response 2: We have carefully reviewed the entire manuscript and standardized the terminology accordingly. All instances of “gender” have been replaced with “sex” to ensure consistency and conceptual accuracy throughout the text.

Comment 3: The order of the freestyle and butterfly tests were not randomized? Do the authors believe that the lack of randomization could have influenced the comparison between techniques?

Response 3: Thank you for addressing the significant concern regarding the non-randomized sequence of freestyle and butterfly sprint tests. We recognize that randomization is generally favoured for minimizing potential order or fatigue effects. The sequence (front crawl followed by butterfly) in our study was not randomized due to safety and logistical constraints. The butterfly stroke in young swimmers necessitates increased technical and physiological requirements and presents a heightened possibility of technical difficulties when performed first.

To minimize potential order effects, swimmers received complete recovery time between trials and techniques (≥10 minutes), all efforts were maximal, and coaches observed swimmers for indications of neuromuscular or physiological tiredness before advancement. Previous studies on short sprint lengths (≤25 m) demonstrate minimal residual fatigue with adequate recovery [17, 30, 39]. Consequently, we state that the testing sequence did not significantly influence the comparisons of techniques.

Comment 4: The authors confirm that 50 m sprint times were collected, and line 261 confirms this information exists. Yet, these data are not presented anywhere in the manuscript. Even if sprint time is not included as a dependent variable in multivariate models, it should nevertheless be reported as a descriptive performance indicator. Including these times (for each group) is essential for contextualizing the competitive level of the sample and for enhancing the manuscript’s practical value to readers.

Response 4: Thank you for recognizing that the 50-meter sprint data were not clearly included in the previous version of the manuscript. We agree that providing a key performance indicator is essential to contextualize the swimmers' competitive level. In the revised manuscript, we specifically highlight the 50-m swimming velocity, which we chose as it is the most prevalent and useful statistic in sprint performance evaluations. Swimming velocity serves as a direct, standardized performance metric that facilitates comparisons among groups and aligns to current recommendations in sprint-swimming research. The velocity values have been integrated into the descriptive data and included in Table 2, facilitating proper interpretation of the sample's performance level by readers. We appreciate the reviewer's feedback, and this modification has enhanced the manuscript's clarity and practical significance.

Comment 5: Where any differences between girls and boys in the regression analysis and the entered variables?

Response 5: “We have now added a new paragraph in the Discussion section (lines 343–353) that explicitly clarifies the novel contribution of the study and explains how the inter-sex comparisons advance current understanding of performance determinants in age-group sprint swimmers.

Comment 6: Where any differences between girls and boys in the regression analysis and the entered variables?

Response 6: “We thank the reviewer for this helpful suggestion. In response, we have added two well-developed paragraphs (Line 454-477) to the Discussion providing clear and actionable guidance for coaches and researchers. These paragraphs specify training considerations for boys, girls, and general recommendations applicable to both sexes.”

Comment 7: Another point that deserves deeper discussion: the boys and girls in the sample differ in maturity offset. Boys are farther from their PHV yet still outperform the girls across most variables. This raises several questions: How do maturity differences influence the observed results? Would the gaps be even larger if boys and girls had similar maturity status? What is the validity of directly comparing groups (already from different sexes) with different biological maturation levels? How do these findings add new insight relative to what the literature has already established? - The manuscript needs a clearer explanation of why these comparisons are meaningful and how they should be interpreted by researchers, coaches and practitioners.

Response 7: Thank you for raising this important point regarding differences in maturity offset between boys and girls. We agree that biological maturation is a major determinant of performance in youth sports and that maturity status must be carefully considered when interpreting sex-based comparisons. In our sample, boys were further away from their predicted PHV, however they consistently outperformed girls in most factors. This pattern corresponds with established evidence indicating that boys generally exhibit greater absolute strength, limb length, and propulsive force prior to reaching peak height velocity, attributable to earlier divergence in neuromuscular function, hormonal conditions, and anthropometric dimension.

We recognize that the disparity in maturity may somewhat affect the extent of the observed sex differences. If boys and girls were aligned in terms of maturity status, the performance disparity would likely be exacerbated, as boys undergo significant increases in muscle mass, strength, and stroke efficiency during and subsequent to peak height velocity (PHV). To address this, we incorporated maturity offset as a covariate in the multivariate modelling, ensuring that the discriminatory variables reflect true sex-related differences beyond maturational timing. Our findings therefore highlight which physical, neuromuscular, and technical factors remain most influential after accounting for maturation, offering meaningful insight into how sex-specific sprint profiles emerge during early adolescence.

This comparison is valuable for researchers and practitioners because talent identification and training prescription in youth swimming occur in mixed-maturity and mixed-sex environments. Understanding how boys and girls differ at comparable chronological ages but not necessarily identical biological ages helps coaches contextualize expected performance gaps, avoid misinterpretation of maturational advantages as “talent,” and tailor strength and technique development pathways more appropriately.

Attachment

Submitted filename: Response to Reviewers.docx

pone.0339480.s005.docx (26KB, docx)

Decision Letter 2

Dalton Pessôa Filho

8 Dec 2025

Sex-Based Differences in Front Crawl and Butterfly Sprint Performance in Age-Group swimmers

PONE-D-25-34920R2

Dear Dr. Chainok,

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Additional Editor Comments (optional):

Reviewers and editors approved the current version of the manuscript.

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #2: Yes

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Reviewer #2: Yes

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Reviewer #2: Yes

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Reviewer #1: I have no further comments although I Disagree with your expresions on AnCV in lines 162 and 147. This is not a valid indicator of "anaerobic capacity", AnCV is just related to sprint swimming.

Reviewer #2: The authors have addressed my concerns. The manuscript is much improved now, congratulations.

(Just a small note: in lines 455–456, “For boys” appears twice.)

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Reviewer #2: No

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Acceptance letter

Dalton Pessôa Filho

PONE-D-25-34920R2

PLOS One

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Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 Data. Descriptive data for general characteristics, swimming performance and tethered force in age-group front crawl and butterfly swimmers.

    (XLSX)

    pone.0339480.s001.xlsx (13.5KB, xlsx)
    S2 Data. Descriptive data for neuromuscular performance in age-group front crawl and butterfly swimmers.

    (XLSX)

    pone.0339480.s002.xlsx (13.6KB, xlsx)
    Attachment

    Submitted filename: Response to Reviewers_PONE-D-25-34920docx.docx

    pone.0339480.s004.docx (45.3KB, docx)
    Attachment

    Submitted filename: Response to Reviewers.docx

    pone.0339480.s005.docx (26KB, docx)

    Data Availability Statement

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