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Original Research

Effects of a 6-Week Plyometric Training Program on Performances in Pubescent Swimmers

Potdevin, François J1; Alberty, Morgan E2; Chevutschi, Alain2; Pelayo, Patrick2; Sidney, Michel C2

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Journal of Strength and Conditioning Research: January 2011 - Volume 25 - Issue 1 - p 80-86
doi: 10.1519/JSC.0b013e3181fef720
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Plyometric training (PT) was introduced by Verkoshanski (35) as a training mode to enhance explosive strength in exercise. The literature is consensual about the effect of PT in improving power output and increasing explosiveness (1). This improvement is obtained by optimizing the stretch-shortening cycle (SSC), which occurs when the active muscle switches from rapid eccentric muscle action (deceleration) to rapid concentric muscle action (acceleration) (19,36). To improve these SSC capabilities within muscle, PT is based on a series of repetitive hops, skips, and jumps (25,38).

Previous studies showed that PT was effective to improve explosive strength in men and women (16,39), pubescents, and adults (26,27) and in athletes from different sports. For example, in a meta-analysis review, Markovic (19) showed that vertical jump height was significantly improved by following PT from 4 to 24 weeks. It has been demonstrated that this improvement in vertical height jump was positively transferred to sport-specific jumping (6,18), cycling (15), running (14,17,18), or soccer (30). Nevertheless, despite numerous evidences showing the benefits of PT in a range of sporting landing activities, the impact of such a strength training approach to swimming has been given little attention (3). Yet, the PT program appears to be relevant in swimming because it allows muscle power improvement without significant change in body composition (30), considering that muscle mass can affect the straight position of the swimmer and add active drag (34).

Referring to the principles of the specificity of training, additive effects of dryland training to ongoing swim training have been shown to be controversial (12,31). Recently, Bishop et al. (3) showed a positive effect of 8 weeks of PT on the block start performances in adolescent swimmers when added to habitual swimming training. In contrast, Cossor et al. (12) showed no effect of a 20 weeks' PT on turning capabilities and 50-m front crawl performances in adolescent swimmers. Considering that the benefits of PT program in swimming have not been deeply investigated, the aim of this study was to identify the effect of low-limb PT when added to habitual training on overall swim performances in adolescent population.


Experimental Approach to the Problem

The research hypotheses were examined by way of an experimental design including 2 independent groups: a control group (GCONT) and a combined swimming and plyometric group (GSP). After the completion of baseline trials, which measured a range of swim and jump performances (dependent variables), subjects were assigned through random selection to one of the groups. After which, the 2 groups followed either their habitual swim training (GCONT) or supplement habitual swim training with a PT (GSP). After the 6 weeks' intervention period, both groups were reassessed by completing the swim and jump performance trials. Jump variables were associated with swimming variables to test a positive transfer between muscle power improvement and swimming skills.


All the subjects belonged to the same swimming team, which is engaged in 5.5 hours of training per week (2 × 2 hours and 1 × 1.5 hours). Before the beginning of any engagement with the subjects, ethics consent was granted through the University ethics committee. Subjects were informed of any potential risks involved in participation, and all provided written informed consent including consent of parents in accordance with institutional regulation. Criteria for inclusion were applied to ensure all swimmers were aged 13-15 years and were Tanner staged 3-4 (32). Subjects were submitted to a complete medical examination before the beginning of the experiment, and boys and girls were randomly assigned to either the GCONT (6 girls, 5 boys) or the GSP (7 girls, 5 boys). The study experienced no withdrawals, and subjects characteristics are displayed in Table 1.

Table 1
Table 1:
Characteristics of pubescent competitive swimmers.*†


GSP participated in swimming training combined with PT program. GCONT participated only in swimming training. Both groups swam together for 5 hours 30 min·wk−1 for the 6 weeks of the study. The swimming training was identical for both groups and was conducted by the same coach in the same time to ensure consistency in coaching techniques and programing. Before 2 training sessions per week, GSP engaged in a low-limb PT session with 1 instructor supervising the group. Subjects were required to conduct a 10-minute standard dynamic according to the recommendations of Radcliffe and Farentinos (23). Frequency, intensity, volume, and recovery for each plyometric exercise were similar to literature recommendations (7,10,22). The program of the low-limb PT period is presented in Table 2. Altogether, the subjects performed 2,146 jumps during the 6-week training period.

Table 2
Table 2:
The 6-week low-limb plyometric training program for GSP.*
Caption not available.

Before initial testing, subjects were familiarized with the protocol. Subjects were tested on the following: anthropometric measurements; vertical jump measurements (m); gliding task (m·s−1); and swimming tests (m·s−1). The tests were conducted in the same order, and at the same hour, before and after the training period.

Anthropometric Tests

The examination was conducted by the same physical therapist. Height and arm span were measured to the nearest centimeter. Body mass was measured, and percentage body fat was estimated with an impedance metric balance scale (type Tanita, Tokyo, Japan).

Vertical Jump Tests

Lower-limb performances were evaluated using an “Ergojump” (Junghans GMBH-Schramberg, Germany). Three trials were performed for a countermovement jump (CMJ) and for a squat jump (SJ) according to the protocol of Bosco et al. (8). During all jumps, subjects were required to hold their hands on their hips and to keep up their maximal knee flexion (90°), to control for differences in jumping technique between trials. All subjects were verbally encouraged to jump with maximal effort. Only the best performance for each jump was retained for statistical analysis.

Gliding Task

Subjects were asked to hold their breath and to push-off the pool wall in a prone streamlined position with both arms extended over the head, feet together, and ankle plantar flexed. The aim of the task was to cover the highest distance. During this test, swimmers were connected to a speed sensor (Scaime, type PT 9301, Annemasse, France), which consists of an unstretchable cable driving an electromagnetic angular velocity tachometer. The measurements were taken using a stainless steel light cable coiled around the tachometer and connected at the distal end to a harness belt attached to the swimmer's waist. It provided a linear velocity measurement of the hip. The sampling rate was set at 60 Hz. The resistance applied to the swimmer's forward displacement was 10 N (validated by the constructor and tested in the laboratory). From speed data, the maximal speed attained during the glide and the average acceleration between the beginning of the push on the wall and the maximal speed (ΔV/Δt, m·s−2) were calculated for each participant. Three trials were collected.

Swimming Tests

Swimmers performed 2 front crawl swimming tests with a diving start (400 and 50 m), and 2 tests with a water start without push-off on the wall (25 m in front crawl and 25 m only with kicks). All the starts were on the initiative of the swimmer. Two independent observers recorded times, and these 2 values were averaged to calculate averaged swimming speed (V400, V50, V25, VKICK, m·s−1). The start signal for the observers was the time when the swimmer's feet left the wall or the block. For the water start without push-off, the start signal consisted of the swimmer's limbs moving.

Statistical Analyses

Data are shown as mean ± SD. Normal Gaussian distribution and homoscedasticity of the data were verified by the Shapiro-Wilk and Levenne tests, respectively. Reliability of the data across the consecutive trials for each jump performances was verified using the intraclass correlation coefficient according to the recommendations of Schrout and Fleiss (29). To assess whether the PT had a significant effect on swimming and jumping performances, data (anthropometric parameters, jumping tests, gliding tests, and swimming tests) were subjected to a 2-tailed independent t-test between GCONT and GSP before and after the 6 weeks' training. To estimate the magnitude of the PT effect in the case of within-group comparison, Effect Size (ES) values were calculated according to the following formula:

where MPre, MPost, SDPre, and SDPost are pre and postintervention mean and SD values.

The ES values were interpreted using the Cohen scale (11): the magnitude of the difference was considered as trivial (ES < 0.2), small (0.2 ≤ ES < 0.5), moderate (0.5 ≤ ES < 0.8), and large (ES ≥ 0.8). To assess whether jumping performances improvements were associated with swimming performances improvements, Pearson correlation was performed between jump performances evolutions during the intervention period (ΔCMJ and ΔSJ, cm) and swimming performances evolutions (ΔV50, ΔV400, ΔV25 (m·s−1) and Δ gliding task (m·s−1 and m·s−2) for the 2 groups. All analyses were performed using Statistica version 7.0, and significance was set at the 0.05 and 0.01 levels.


The means and SDs for the various measurements are presented in Table 3. For all variables, there was no group effect before the intervention period. Only GSP showed a significant increase of the performances for the CMJ (32.45 ± 4.2 vs. 28.92 ± 4.82 cm, p < 0.01, ES = 0.73) and the SJ (31.13 ± 4.88 vs. 26.18 ± 3.82 cm, p < 0.01, ES = 1.3). For the 2 jumping tests, there were significant differences between both groups after the training period (32.45 ± 4.2 vs. 25.88 ± 3.82 cm; 31.13 ± 4.88 vs. 25.19 ± 4.17 cm, p < 0.01, for CMJ and SJ, respectively). Only GSP group showed a significant increase of the maximal glide speed (2.28 ± 0.19 vs. 2.41 ± 0.27 m·s−1, p < 0.05, ES = 0.26). For the 2 groups, there were a significant improvements in the average acceleration during the gliding task (6.80 ± 1.12 vs. 4.81 ± 0.90 m·s−2 ES = 1.99; 5.71 ± 1.38 vs. 4.49 ± 0.62 m·s−2, ES = 1.22; p < 0.01; for GSP and GCONT, respectively). V400 and V50 increased significantly only for GSP between pre and postintervention period (0.96 ± 0.09 vs. 0.92 ± 0.10 m·s−1, ES = 0.15; p < 0.05; 1.29 ± 0.15 m·s−1 vs. 1.25 ± 0.18 m·s−1, ES = 0.1, p < 0.05; for V400 and V50, respectively). Significant correlations were found between ΔSJ (cm) and ΔV50 (m·s−1) only for GSP (R = 0.73, p < 0.05).

Table 3
Table 3:
Results for the various tests for GSP and GCONT before and after the training period.*†


The purpose of this study was to monitor the response of pubescent children to low-limb PT and possible subsequent improvements in specific swimming tasks. The duration of the present investigation is comparable to those in previous studies (from 4 to 20 weeks [19]) and more specifically to those conducted on pubescent children (6-10 weeks [8,15,17,20]. At the beginning of the experimentation, both groups did not differ significantly inall the studied variables. Our main findings showed that a 6-week of PT enhances performances in the CMJ and SJ for GSP. Such improvements have been concomitant with swimming task as the maximal velocity and the average acceleration during the glide speed test, and for the front crawl tests with dive (V50 and V400, m·s−1).

No significant difference has been observed for anthropometric data between both groups. The PT program did not influence the growth of children because our results showed that our whole population followed normal growth with periods of increase in children aged 14 (13).

The results showed that jumping tests performances for CMJ and SJ were improved significantly by PT. These increases can be considered as moderate to large according to the ES values and are close to those reported in studies conducted in children (15,17,20) except for the study of Cossor et al. (13) with younger participants with lesser increases (11.7 ± 1.16 years). It is well accepted that jump performances represent a good predictor of muscle power (26). Because of identical growth and identical body evolution for the 2 groups, it can be supposed that the observed improvements in CMJ and SJ only for GSP result from a significant gain in maximal power delivered by the legs. This result is in accordance with the potential of preadolescents for an increase in strength owing to neural factors, such as increases in motor unit activation and changes in motor unit coordination, recruitment and firing (21,24). Nevertheless, the kind of muscular adaptations (neural and/or muscle hypertrophy) underlying these improvements in this study remains unknown as no further anthropometric measurements were made.

Greater improvement in SJ than in CMJ have been observed for GSP (ES = 1.66 and ES = 2.37, for CMJ and SJ, respectively). This result is not in accordance with Markovic (19) who showed that the effect of PT for vertical jump height is higher for SJ than for CMJ. Nevertheless, his meta-analysis is based upon studies using only landing activities. Moreover, Sanders (28) supposed that the turn phase (flip turn) may be likened to a CMJ because there is a period of flexion after initial contact in which the major extensors of the hip, knee, and ankle are working eccentrically. This eccentric phase is followed by concentric work of muscles to extend the hip, knee, and ankle to generate speed away from the wall. Because swimmers practiced more flip turn, they would be more trained in a CMJ jump rather than in a SJ. This could explain the higher effect of PT on SJ.

The PT effect on V400 and V50 (m.·s−1) is one of the major findings of this study because PT is associated with improvements in race events. Cossor et al. (12) showed controversial results but the participants were younger and were only tested in a 50-m front crawl race. Improvements in gliding task are observed for the 2 groups concerning the average acceleration (m·s−2), whereas improvement in maximal attained speed during the gliding are only noted for GSP. Improvements for GCONT could be explained by the repetition of turns and start phases in habitual swimming training in which hydrodynamic body position is searched. In that way, maximal acceleration could be improved with decrease of active drag, without increase of muscle power (34). However, the impact of PT is statistically demonstrated as it allowed greater improvement in the average acceleration for GSP than for GCONT (ES = 1.99 and ES = 1.22, for GSP and GCONT, respectively).

Improvements only for GSP in V50 (m·s−1) is significantly correlated with improvements in SJ (cm). This result is in accordance with Bishop et al. (3) who showed improvements in start performance with PT by developing higher power of the block. Start block static position could be compared to a SJ position and improvements in V50 (m·s−1) could be attributed to higher performance in start phase. In that way, SJ improvements could appear as an indicator of progress which could be transferred to the specific dive task. The no effect of PT on the VKICK and V25 (m·s−1) in comparison with effect of V400 and V50 suggest strongly the effect of PT on starting and turning phases. The literature showed that these phases of race events are related to swimming performance (2,33). Indeed, freestyle turns represent 20.5% of the total race time in a 50-m race in a short course pool (33) and a greater contribution has been reported for longer races (9). Although the actual time spent on the wall is approximately 0.3-0.5 seconds, or 1.5% of the 50-m total time, research has demonstrated that the average velocity after the turn and the total turn velocity were significantly correlated with the event time (9,12,37). These results were confirmed by Blanksby et al. (4) by reporting significant correlations between the total event time and both 2.5- and 5-m round trip times for freestyle swimmers. Thus, the strength development generated on the plot start and on the wall appeared to be of most importance in the propulsion of swimmers (12). The PT appeared to be an efficient training to improve this kind of motor skill.

Practical Applications

This study indicates that PT could be relevant to improve swimming performances in adolescent swimmers by enhancing performances in starting and turning phases. The plyometric program in this study was very practical because training was easily incorporated into a training session and lasted approximately 20-25 minutes. Plyometrics are also inexpensive, because they do not require any specialized equipment. Given the results of this study, coaches may consider incorporating plyometrics into a preseason situation to gain rapid improvements. It appears that an appropriate short-term plyometrics training program can enhance leg performances in as little as 6 weeks.


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    strength training; jump tests; swimming

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