Abstract
g performance can be improved not only by in-water sport-specific training but also by means of dry land-training (e.g., plyometric jump training [PJT]). This study examined the effects of an 8-week PJT on proxies of muscle power and swim- ming performance in prepubertal male swimmers. Participants were randomly allocated to a PJT group (PJT; n = 14; age: 10.3 ± 0.4 years, maturity-offset = -3±0.3) or a control group (CG; n = 12; age: 10.5 ± 0.4 years, maturity-offset = -2.8 ± 0.3). Swimmers in PJT and CG performed 6 training sessions per week. Each training session lasted between 80 and 90 minutes. Over the 8 weeks in-season training period, PJT performed two PJT sessions per week, each lasting between 25 to 30 minutes (⁓1 hour per week) in replacement of sport-specific swimming drills. During that time, CG followed their regular sport-specific swimming training (e.g., coordination, breathing, improving swimming strokes). Overall training volume was similar between groups. Pre- and post-training, tests were conducted to assess proxies of muscle power (countermovement-jump [CMJ]), standing-long- jump [SLJ]) and sport-specific swimming performances (15-, 25- , and 50-m front-crawl, 25-m kick without push [25-m kick WP], and 25-m front-crawl WP). No training or test-related injuries were detected over the course
coordination, breathing, improving swimming strokes). Overall training volume was similar between groups. Pre- and post-training, tests were conducted to assess proxies of muscle power (countermovement-jump [CMJ]), standing-long- jump [SLJ]) and sport-specific swimming performances (15-, 25- , and 50-m front-crawl, 25-m kick without push [25-m kick WP], and 25-m front-crawl WP). No training or test-related injuries were detected over the course of the study. Between-group anal- yses derived from magnitude-based inferences showed trivial-to- large effects in favour of PJT for all tests (ES = 0.28 to 1.43). Within-group analyses for the PJT showed small performance im- provements for CMJ (effect-size [ES] = 0.53), 25-m kick WP (ES = 0.25), and 50-m front crawl (ES = 0.56) tests. Moderate perfor- mance improvements were observed for the SLJ, 25-m front- crawl WP, 15-m and 25-m front-crawl tests (ES = 0.95, 0.60, 0.99, and 0.85, respectively). For CG, the within-group results showed trivial performance declines for the CMJ (ES=-0.13) and the 50-m front-crawl test (ES = -0.04). In addition, trivial-to- small performance improvements were observed for the SLJ (ES = 0.09), 25-m kick WP (ES = 0.02), 25-m front-crawl WP (ES = 0.19), 25-m front-crawl (ES = 0.2), (SLJ [ES = 0.09, and 15-m front crawl (ES = 0.36). Short-term in-season PJT, integrated into the regular swimming training, was more effective than regular swimming training alone in improving jump and sport-specific swimming performances in prepubertal male swimmers. Key words: Stretch-shortening cycle, young athletes, rate of force development, sport-specific performance. Introduction From a physical, physiological, and technical-tactical point of view, swimming is a highly demanding Olympic sport and elite performances are achieved at an early age (Nugent et al., 2018). Therefore, commitment to training has to start during the early stages of long-term athlete de- velopment (LTAD) to increase the likelihood of sporting success as an elite athlete (Nugent et al., 2018). From a per- formance and health-related perspective, muscle strength should specifically be promoted during all LTAD stages (Lloyd et al., 2012; 2015; Pichardo et al., 2018). In fact, muscle strength should be promoted in young athletes to support motor skill acquisition, to enhance
velopment (LTAD) to increase the likelihood of sporting success as an elite athlete (Nugent et al., 2018). From a per- formance and health-related perspective, muscle strength should specifically be promoted during all LTAD stages (Lloyd et al., 2012; 2015; Pichardo et al., 2018). In fact, muscle strength should be promoted in young athletes to support motor skill acquisition, to enhance physical fitness and sports performance, to improve markers of health and well-being, and to reduce the risk of sustaining sports-re- lated injuries (Faigenbaum et al., 2013; 2019; Granacher et al., 2016). More specifically, it has been reported that well- developed levels of muscle strength and power play an im- portant role in achieving high swimming performances (Crowley et al., 2018; Girold et al., 2007; Potdevin et al., 2011). In fact, there is evidence that the ability to exert force in the water is a decisive factor, particularly in sprint swimming (e.g., 50-m, 100-m, and 200-m) (Morouço et al., 2011). Moreover, the swimming start contributes up to 30% of the total race time (Cossor et al., 1999). The shorter the distance the more important becomes an explosive start. West et al. (2011) showed that a successful swim- ming start depends on a number of factors including reac- tion time, vertical and horizontal forces generated by lower limb muscles during the push-off phase from the block, and a low resistance during the underwater gliding phase. In addition, during front-crawl swimming, lower limb mus- cles contribute up to 12% of the propulsion (Ribeiro et al. 2015). Swimming performance cannot only be improved through sport-specific in-water training but also by means of dry land-training (i.e., strength and/or power training) (Crowley et al., 2018; Potdevin et al., 2011). Previous stud- ies have shown that particularly plyometric jump training (PJT) is a widely used, safe, and effective training regime to improve muscle strength and power as well as sport-spe- cific performance in prepubertal athletes (Bedoya et al., 2015; Bouguezzi et al., 2018; Chaabene and Negra, 2017; Nugent et al., 2018). In this context, Granacher et al. (2016) introduced a conceptual model for the implementation of resistance
plyometric jump training (PJT) is a widely used, safe, and effective training regime to improve muscle strength and power as well as sport-spe- cific performance in prepubertal athletes (Bedoya et al., 2015; Bouguezzi et al., 2018; Chaabene and Negra, 2017; Nugent et al., 2018). In this context, Granacher et al. (2016) introduced a conceptual model for the implementation of resistance training during the different LTAD stages. The Research article
Plyometric training and swimming performance 806 same authors suggested a variety of resistance training ap- proaches that can be used across the different maturation stages, among them PJT (Granacher et al., 2016). How- ever, it is noteworthy that PJT should not be used as a stand-alone component of an exercise program and the ad- visable approach is to incorporate supervised and progres- sive power training into a well-rounded program that also involves other types of strength and conditioning (Behm et al., 2008; 2017). Only a few studies examined the effects of PJT ex- ecuted outside the pool on swimming performance (Bishop et al., 2009; Potdevin et al., 2011; Rejman et al., 2017). For instance, Bishop et al. (2009) studied the effects of an 8- week combined PJT and swimming training on swim start performance in adolescent swimmers and observed signif- icant improvements in velocity from take-off to water con- tact (∆15.6%) and 5.5-m performance time (15.4%). Re- butini et al. (2016) conducted a 9-week PJT program with adolescent male and female swimmers and showed im- provements in peak torque and rate of torque development of the hip (∆47% and 108%, respectively) and knee joints (∆24% and 41%, respectively) during swim start perfor- mance. Most of the available studies focused on the effects of PJT on swim start performance and the underpinning ki- netic and kinematic parameters (Bishop et al., 2009; Re- butini et al., 2016). Notably, Potdevin et al. (2011) exam- ined the effects of a 6-week PJT on particularly sport-spe- cific swim performances in adolescent male swimmers (age =14.3 ± 0.2 years). These authors revealed significant increases in 50-m (ES = 0.1, ∆3.1%) and 400-m (ES = 0.15, ∆4.2%) average swimming speed as well as in counter- movement jump and squat jump performances (ES = 1.66 and 2.37, respectively). To the authors’ knowledge, there is no study available that investigated the effects of PJT on proxies of muscle power and sport-specific swimming per- formance in prepubertal male swimmers. Therefore, it is timely and imperative to elucidate whether the findings of Potdevin et al. (2011) in adolescent swimmers can be
and squat jump performances (ES = 1.66 and 2.37, respectively). To the authors’ knowledge, there is no study available that investigated the effects of PJT on proxies of muscle power and sport-specific swimming per- formance in prepubertal male swimmers. Therefore, it is timely and imperative to elucidate whether the findings of Potdevin et al. (2011) in adolescent swimmers can be trans- lated to prepubertal swimmers as well. Accordingly, this study sought to examine the effects of an 8-week PJT pro- gram in combination with swimming compared with swim- ming only on proxies of muscle power (i.e., countermove- ment jump [CMJ], standing long jump [SLJ]) and sport- specific swimming performances in prepubertal male swimmers. With reference to the relevant literature (Potdevin et al., 2011; Rebutini et al., 2016), we hypothe- sized that the combination of PJT and swimming results in larger jump and sport-specific performance improvements than regular swimming training alone in prepubertal male swimmers. Methods Experimental approach to the problem A randomized controlled trial was conducted to examine the effects of an 8-week PJT program on proxies of muscle power and sport-specific swimming performances in pre- pubertal male swimmers. One week before baseline test- ing, two familiarization sessions were performed to get participants accustomed to the physical fitness tests and the plyometric drills. The respective test sessions were 5 days apart. Before and after the intervention, tests were con- ducted to assess jump (i.e., CMJ, SLJ) and swimming per- formances. Sport-specific testing included a timed 15, 25, and 50-m front crawl tests with a diving start, a timed 25- m front crawl test without push-off from the wall (25-m WP), and a 25-m kick timed test without push-off from the wall (25-m KWP). All tests were conducted in an indoor swimming pool with a water temperature of 26°C which is in agreement with recommendations from the Federation Internationale de Natation (2014). Testing was conducted 48 hours after the last training session and at the same time of the test day (7:30-9:30 p.m.). Participants A total of twenty-six prepubertal male swimmers partici- pated in this study. They were randomly allocated to
swimming pool with a water temperature of 26°C which is in agreement with recommendations from the Federation Internationale de Natation (2014). Testing was conducted 48 hours after the last training session and at the same time of the test day (7:30-9:30 p.m.). Participants A total of twenty-six prepubertal male swimmers partici- pated in this study. They were randomly allocated to a PJT group (PJT; n = 14; age = 10.3 ± 0.4 years; maturity offset = -3.1 ± 0.3) or an active control group CG (n = 12; age = 10.5 ± 0.4 years; maturity offset = -2.8 ± 0.3). The PJT per- formed six training sessions per week, including two PJT sessions, which were integrated into the regular sport-spe- cific training schedule in replacement of some swimming specific drills. The remaining training time comprised technical drills. CG followed their regular sport-specific swimming training (i.e., six sessions per week) throughout the intervention period. Training volume was similar be- tween groups. Prior to the start of the study, all young ath- letes performed twice per week strength endurance exer- cises for muscles of the upper and lower limbs and the trunk using the own body-mass. The strength training pro- gram included push-ups, abdominal curls, back extensions, and squats. Participating athletes completed up to 5 sets of 15 repetitions each with a 30 seconds rest in-between sets. Training was conducted over 3 weeks to get the partici- pants prepared for the subsequent plyometric training pro- gram. All participants were competing on a national level within their respective age category. They had a back- ground of 2.0 ± 1.6 years of systematic swimming training involving five to six training sessions per week throughout the season. Further, all participants were healthy and free of musculotendinous injuries over the last 6 months prior to the start of the study. Participants who missed more than 20% of the total PJT sessions and/or more than two con- secutive PJT sessions were excluded from the study. The maturation status was determined at the beginning and af- ter 8 weeks of training according to the maturity offset method (Malina
musculotendinous injuries over the last 6 months prior to the start of the study. Participants who missed more than 20% of the total PJT sessions and/or more than two con- secutive PJT sessions were excluded from the study. The maturation status was determined at the beginning and af- ter 8 weeks of training according to the maturity offset method (Malina et al., 2014). Maturity offset (expressed in years) was defined as the time before or after peak-height- velocity. All participants and their legal representatives were properly informed about all testing and training pro- cedures, as well as potential benefits and harms related to the study. Verbal and written informed consent (legal rep- resentatives) and assent (children) were obtained before the start of the experiment. All procedures were approved by the local Institutional Review Committee of the Higher In- stitute of Sport and Physical Education, Ksar Said, Tunisia. All procedures were in accordance with the latest version of the Declaration of Helsinki. Anthropometric measures Anthropometrical measurements (i.e., body-mass, height)
Sammound et al. 807 were taken by a trained anthropometrist assisted by a re- corder. Standardized procedures were applied in accord- ance with the International Society for the Advancement of Kinanthropometry (ISAK) (Stewart et al., 2011) (Table 1). Proxies of muscle power Countermovement jump: For CMJ testing, participants started from an upright erect standing position, performed a fast downward movement by flexing the knees and hips immediately followed by a rapid leg extension resulting in a maximal vertical jump. Throughout the execution of the test, participants maintained their hands on the hips and el- bows turned outward. CMJ techniques were visually con- trolled by the first author of this study. Jump height was recorded using an Optojump photoelectric system (Micro- gate, SRL, Bolzano, Italy). The intraclass correlation coef- ficient (ICC) for test-retest reliability was 0.98 and the typ- ical error of measurement (TEM) was 2.9%. Standing long jump: The starting position of the SLJ required subjects to stand with their feet shoulder- width apart behind a starting line and their arms loosely hanging down at the sides of their body. On the command ready, set, go, participants executed a countermovement with their legs and arms and jumped at maximal effort in horizontal direction. Participants had to land with both feet simultaneously and could not fall forward or backward. The horizontal distance between the starting line and the heel of the rear foot was recorded via tape measure to the nearest 1-cm. The ICC for test-retest reliability was 0.96 and the TEM was 0.5%. Sport-specific swimming tests Swimming time trials expressed in seconds were adopted as our measures of sport-specific performance. All tests were conducted in a 50-m indoor-swimming pool. Swim- mers performed two front crawl swimming trials with a diving start (15, 25, and 50-m) and two trials with a water start without a push-off from the wall (25-m WP and 25-m KWP). All starts were voluntarily initiated by the swim- mers. Two independent observers recorded performance times using stop-watches. The average of the two recorded values was used for further statistical analyses. The start signal for the observer was
start (15, 25, and 50-m) and two trials with a water start without a push-off from the wall (25-m WP and 25-m KWP). All starts were voluntarily initiated by the swim- mers. Two independent observers recorded performance times using stop-watches. The average of the two recorded values was used for further statistical analyses. The start signal for the observer was the moment as the swimmers’ feet left the block. For the water start without push-off, swimmers’ first lower limb movement was used as an in- dicator to start timing. The distance was standardized using markers at the bottom of the pool. The final signal for the observer was the moment when the swimmers’ hand touched the wall. The ICC for test-retest reliability ranged between 0.89 and 0.91 and the TEM ranged between 1.2 and 2.5% for all swimming tests. Plyometric jump training The PJT intervention was conducted during the competi- tive period of the year (March-April 2018). The program lasted 8 weeks with two sessions per week (Table 1). Plyometric jump training sessions were integrated into the regular training routine of the swimmers in replacement of some swimming specific drills. The remaining training time comprised technical drills (coordination, breathing, improving swimming strokes). The second PJT session was completed 72 hours after the first one to provide a suf- ficiently long enough recovery period between sessions. Each swimming training session lasted between 80 and 90 minutes. PJT drills lasted between 25 and 30 minutes. Dur- ing that time, CG conducted their regular sport-specific training. Thus, both experimental groups experienced sim- ilar training volumes. Overall, 6 training sessions were conducted per week, each lasting between 80 to 90 minutes. No competitions were scheduled over the entire study period. Our PJT protocol was in accordance with pre- viously published PJT recommendations for young athletes (Bedoya et al., 2015). At the beginning of the intervention, a focus was placed on proper exercise technique (e.g., land- ing). All jump exercises were performed on a stable surface (i.e., grass) and at maximal effort (CMJs) with minimal ground contact time. Both PJT sessions comprised 8-12 sets with
in accordance with pre- viously published PJT recommendations for young athletes (Bedoya et al., 2015). At the beginning of the intervention, a focus was placed on proper exercise technique (e.g., land- ing). All jump exercises were performed on a stable surface (i.e., grass) and at maximal effort (CMJs) with minimal ground contact time. Both PJT sessions comprised 8-12 sets with 6–10 repetitions each. The total ground contacts per week gradually increased from 50 during the first week to 120 during the last week of training (Bouguezzi et al., 2018; Negra et al., 2017). A 90-second rest was provided between each set of exercise to allow sufficient recovery time. Table 1. Characteristics of the plyometric jump training programs. WeekPlyometric exercises Volume (sets×reps) Ground contacts 1 Bilateral ankle hops (hurdle height: 20 cm) 4 × 6-7 50 CMJs 4 ×6-7 2 Bilateral ankle hops (hurdle height: 20 cm) 4 × 7-8 60 CMJs 4 × 7-8 3 Bilateral ankle hops (hurdle height: 20 cm) 4 × 8-9 70 CMJs 4 × 9 4 Bilateral ankle hops (hurdle height: 20 cm) 4 × 10 80 CMJs 4 × 10 5 Bilateral ankle hops (hurdle height: 20 cm) 4 × 10 90 CMJs 6 × 8-9 6 Bilateral ankle hops (hurdle height: 20 cm) 6 × 8-9 100 CMJs 6 × 8-9 7 Bilateral ankle hops (hurdle height: 20 cm) 6 × 8 110 CMJs 6 × 10 8 Bilateral ankle hops (hurdle height: 20 cm) 6 × 10 120 CMJs 6 × 10 Reps: repetitions; Notes: CMJ: countermovement jump Statistical analyses Between-group baseline differences in anthropometric characteristics, maturity-offset, and physical fitness were verified using t-tests for independent samples. Magnitude- based inferences were applied to calculate and interpret ef- fect sizes. In this regards, effect sizes <0.2 were considered trivial, between 0.2–0.6 small, between 0.6–1.2 moderate, between 1.2–2.0 large, between 2.0–4.0 = very large and finally >4.0 = extremely large (Hopkins et al., 2009). The estimates were considered unclear when the chance of a
effect sizes <0.2 were considered trivial, between 0.2–0.6 small, between 0.6–1.2 moderate, between 1.2–2.0 large, between 2.0–4.0 = very large and finally >4.0 = extremely large (Hopkins et al., 2009). The estimates were considered unclear when the chance of a
Description
PJT improves jump and swimming performance in young swimmers.