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The Effects of Plyometric Training Followed by Detraining and Reduced Training Periods on Explosive Strength in Adolescent Male Basketball Players

Santos, Eduardo JAM; Janeira, Manuel AAS

Journal of Strength and Conditioning Research: February 2011 - Volume 25 - Issue 2 - p 441-452
doi: 10.1519/JSC.0b013e3181b62be3
Original Research

Santos, EJAM and Janeira, MAAS. The effects of plyometric training followed by detraining and reduced training periods on explosive strength in adolescent male basketball players. J Strength Cond Res 25(2): 441-452, 2011-The aims of this study were to determine the effects of (a) plyometric training on explosive strength indicators in adolescent male basketball players and (b) detraining and reduced training on previously achieved explosive strength gains. Two groups were formed: an experimental and a control group. The former was submitted to a 10-week in-season plyometric training program, twice weekly, along with regular basketball practice. Simultaneously, the control group participated in regular basketball practice only. At the end of this period, the experimental group was subdivided into 2 groups: a reduced training group and a detraining group. All participants were assessed on squat jump, countermovement jump, Abalakov test, depth jump, mechanical power, and medicine ball throw at the beginning and at the end of the 10-week in-season plyometric training and on weeks 4, 8, 12, and 16 of the in-season detraining and reduced training periods. In the first phase of the study, the experimental group significantly increased all the assessed indicators (p < 0.05). In the following phase and in general all the groups maintained the previously achieved results. In conclusion, plyometric training showed positive effects on upper- and lower-body explosive strength in adolescent male basketball players. Moreover, we can state that both detraining and a reduced training program indistinctly contribute to maintenance of strength levels. These results highlight the unique power that basketball-specific training seems to have on the sustainability and maintenance of sport performance.

Faculty of Sport, University of Porto, Porto, Portugal

Address correspondence to Eduardo José Almeida Martins dos Santos, eduardosantos@clix.pt.

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Introduction

Strength training is a main process on the improvement of motor performance and consequently a basic demand of sport skill optimization (21,32). In the same way that strength training improves performance, detraining carries out a decrease in strength levels and thus in athletic performance (20,21,28). Several authors have pointed out decreases in strength levels over detraining periods (21,28). To prevent detraining effects, some authors postulate the introduction of strength maintenance programs on training planning (21,33). Thus, the available literature points out volume and training frequency reduction as essential on the maintenance training design, while maintaining the initial intensity levels (21,26,39,43).

Formerly characterized as a method for adult athletes, plyometric training is now seen as a safe, valuable, and challenging activity for younger athletes when it is appropriately designed and supervised (18). Its application with young athletes has been recommended for explosive strength development (9,31,40). As far as basketball training is concerned, this method has been pointed out as a primary tool in the training process, specifically aimed at increasing vertical jump ability (12,22,44). The relevance of this option on the training of young basketball players has been proved by different studies available in literature (6,37,43).

Regarding detraining and reduced training periods, there is a lack of investigation about their effects on upper- and lower-body explosive strength in the adolescent male population previously submitted to a plyometric training program. To our knowledge, few studies have examined the effects of a training program followed by detraining and/or reduced training periods among prepubertal (14,19) and pubertal boys (30,43). However, the available literature concerning basketball (29,36,43) is scarce on these domains (detraining and reduced training), although the authors highlighted the retention of gains resulting from regular basketball practice.

It seems reasonable to hypothesize that plyometric training increases upper- and lower-body explosive strength in adolescent male basketball players and that detraining and reduced training periods will have similar effects in the maintenance of explosive strength levels. Consequently, the aims of the present study were to determine the effects of (a) plyometric training on explosive strength indicators in adolescent male basketball players and (2) detraining and reduced training on explosive strength gains previously achieved.

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Methods

Experimental Approach to the Problem

The study was designed to assess the effects of a 10-week in-season plyometric training program on the explosive strength development of young male basketball players (aged 14 to 15 years old). To address the first hypothesis previously presented, 2 groups (experimental group [EG] and control group [CG]) were selected. The EG performed plyometric training, twice weekly, along with the regular basketball practice; the CG continued regular basketball practice alone. All the subjects were tested on the squat jump (SJ), countermovement jump (CMJ), Abalakov test (ABA; a countermovement jump with arm swing), depth jump from a 40-cm platform (DJ), mechanical power (MP), and medicine ball throw (MBT) before (T0) and after the 10-week in-season training program (T1). Subsequent to this period, and to address the second hypothesis previously presented, the subjects of the EG were randomly assigned to either a detraining group (DTR; n = 7) or a reduced training group (RT; n = 7). The DTR group stopped the plyometric training program but maintained regular basketball practice. Along with the basketball practice, the RT group was submitted to a reduced plyometric training program once weekly. Therefore, it was our goal to identify and compare the effects of detraining or reduced training periods on the explosive strength levels of young male basketball players. All the subjects were tested on the same variables, after 4 (T4), 8 (T8), and 12 (T12) weeks and at the conclusion of the 16-week in-season detraining/reduced training periods (T16). Intraclass correlation coefficients for all the assessed variables were r = 0.885; r = 0.987 and r = 0.785; r = 0.995, respectively, for the experimental and control training groups, and outcome variables were compared over time and between groups.

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Subjects

Twenty-four young male basketball players volunteered to take part in this study. The subjects were randomly assigned to a control group (n = 10; age 14.5 ± 0.4 years old, weight 61.1 ± 11.4 kg, height 173.2 ± 7.6 cm, and basketball training experience 4.3 ± 1.2 years) or an experimental group (n = 14; age 15.0 ± 0.5 years old, weight 62.6 ± 9.9 kg, height 172.9 ± 6.3 cm, and basketball training experience 7.07 ± 2.8 years). All athletes were in Stages 3 or 4 for pubic hair growth and genital development for both groups (46). None of the subjects had previously participated in plyometric training programs. Athletes, parents, and coaches were informed about the purpose of the study and the eventual risks associated with plyometric training. Informed consent was obtained from all subjects and parents before the study began. The Institutional Review Board of the Faculty of Sports/University of Porto approved all study procedures.

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Testing Procedures

Subjects were assessed for upper- and lower-body explosive strength according to Cronin and Owen (13) and Bosco (5) protocols, respectively, before (T0) and after (T1) a 10-week in-season plyometric training program and on weeks 4 (T4), 8 (T8), 12 (T12), and 16 (T16) of the in-season detraining and reduced training periods. This procedure allowed for the assessment of the following variables: (a) SJ (cm), (b) CMJ (cm), (c) ABA (cm), (d) DJ from a 40-cm platform (cm), (e) MP (W/kg−1), and seated MBT (meters). There was a previous familiarization with accurate test procedures. Tests followed a general warm-up that consisted of running, calisthenics, and stretching. Except for mechanical power, which was assessed after 2 trials with a 60-second rest between trials, all the other tests were performed with 3 trials and all the correspondent mean values were considered for statistical analysis. There was a 20-second and a 10-second rest between trials for the lower-body and the sitting chest throw, respectively. All jumping tests were performed using a contact platform Globus Ergo Tester (Codogne, Italia), except for the DJ, which was performed on an electromechanical platform Ergojump (Digitest OY, Muurame, Finland).

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Training Protocol

The 10-week in-season training program consisted of a series of plyometric exercises (Table 1). Workouts occurred twice weekly on nonconsecutive days. A standardized warm-up routine, consisting of running, calisthenics, and stretching, was used. Plyometric material included 3-kg medicine balls, 40-cm-high boxes, 28-cm-high cones, 30-cm-high benches, and 50-cm-high hurdles, with 1 m between them. The control group was not involved in any plyometric training program. At the end of the 10-week in-season plyometric training program, the experimental group was randomly assigned to either a detraining (n = 7) or a reduced training (n = 7) group. The former group accomplished a 16-week in-season detraining period (complete cessation of strength training), whereas the latter group was submitted to a reduced training program, once weekly, in a similar period of time (Table 2). The control group was kept away from any kind of plyometric activity. The 3 groups pursued the regular basketball practice throughout the study.

Table 1

Table 1

Table 2

Table 2

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Statistical Analyses

Means and standard deviations were used to describe the data. A repeated-measure analysis of variance (ANOVA) with a fixed factor (group) was used to analyze changes in time, especially a significant interaction term (group by time). When significant main effects and/or interactions were observed, post hoc comparisons were performed using a Bonferroni test. The significance level was set at p ≤ 0.05.

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Results

The results between the pre- and post-test for explosive strength scores in both groups and the results between groups at baseline and after the training program are presented in Table 3.

Table 3

Table 3

The experimental group showed significant increases in all the variables scores. Conversely, the control group significantly decreased in squat jump, countermovement jump, Abalakov test, and mechanical power scores. However, the results of the MBT test showed a significant increase for the control group. The groups were similar on pre-test, but significant differences were observed on post-training in all the variables, except for the mechanical power.

Figures 1-3 graphically illustrate the behavior of the studied indicators for each group during the 10-week in-season training program. The results from the comparison of the explosive strength mean scores for the detraining, reduced training, and control groups during a 16-week in-season period, along with the comparison among groups in the different moments of assessment, are presented in Table 4.

Table 4

Table 4

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

A detailed analysis of Table 4 shows that the reduced training group significantly differs from the control group in all the evaluation times and in all the assessed variables, except for the mechanical power test. In the same way, the detraining group significantly differs from the control group in all the evaluation times but only as long as the medicine ball throw is concerned. This statistically significant differentiation is also viewed between these 2 groups in squat jump; at T1, T4, and T16; and in depth jump in all the evaluation times except for T8.

The analysis of each group all over the different moments of evaluation shows statistically significant increments for the control group between T1 and T4 on squat jump and countermovement jump and between T1 and T8 and T1 and T12 on squat jump. The detraining group showed stability during the 16-week in-season period. The reduced training group maintained the squat jump, Abalakov test, and mechanical power test values throughout the 16-week in-season maintenance-training program. Statistically significant increases were observed between T1 and T12 and T1 and T16 on countermovement jump, depth jump, and medicine ball throw. In the latter, the reduced training group also presented statistically significant increases between T1 and T8.

Figures 4-6 graphically illustrate the behavior of the studied variables for the 3 groups during the 16-week in-season period.

Figure 4

Figure 4

Figure 5

Figure 5

Figure 6

Figure 6

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Discussion

The present study showed that the 10-week in-season plyometric training promoted statistically significant increases in vertical jump, mechanical power, and medicine ball throw values. On the contrary, the control group decreased with statistical significance on the squat jump, countermovement jump, Abalakov test, and mechanical power values. However, a significant increase in medicine ball throw was registered for the control group. At the end of the 10 weeks, the experimental group significantly differed from the control group in all the assessed variables except for the mechanical power test.

However, detraining and reduced training groups have generally retained the values obtained at the post-training, all over the 16-week in-season detraining and reduced training periods. Identical behavior was observed as far as the control group is concerned. There were no statistically significant differences between the detraining and the reduced training groups in all the evaluation moments. However, statistically significant differences were evident between the reduced training and the control groups in all the assessment moments and in all the evaluated variables except for the mechanical power test.

In the present study, 10 weeks of in-season plyometric training resulted in significant increments on both upper- and lower-body explosive strength in adolescent male basketball players. These results are similar to those of previous investigations carried out on the youth basketball domain (6,37,43). Plyometric exercises are similar to basketball characteristic movements (47), which proved to be of great importance to our program and may have been fundamental to the achieved outcomes.

Basketball is seen as a sport in which plyometric training is rarely used in season because of the high number and intensity of practices (1). Nevertheless, given the characteristics of the sample (young basketball players performing 2 to 3 weekly workouts and a formal game at the weekend), the in-season plyometric practice proved to be advantageous-that is, our experimental group improved its explosive strength values after adding the plyometric training program to the regular basketball practice, whereas the regular basketball practice alone (training and games) was not enough to keep baseline explosive strength levels in the control group.

The assessed variables set is closely linked both to the leg extensor muscles explosive strength and to the jump power, which are important characteristics in neuromuscular performance (25). This muscular chain is responsible for the efficiency of sprints and jumps that frequently occur in the basketball game (27). Because the plyometric method is an efficient way of training the neuromuscular system (7,23) it is our belief that our training program may have contributed to an improved neuromuscular performance resulting in the observed explosive strength increments. This aspect was also decisive to the results obtained by 13 adolescent male basketball players submitted to a 12-week depth jump plyometric training program (6). The subjects increased the vertical jump with and without arm swing as a result of both enhanced jump ability and strength increments. Thus, the authors believe that plyometric training maximizes the coordination of neuromuscular capability. In this investigation, the control group participated only in the regular basketball training and increased the vertical jump values in a lower rate. At post-training, however, the groups did not differ in the vertical jump without arm swing and the experimental group was significantly better than the control group in the vertical jump with arm swing. The results of this investigation (6) differ from those of the present study because our control group significantly decreased the countermovement jump and the Abalakov test values, which were statistically different from those obtained by our experimental group at post-training.

In another study with young male basketball players (15-16 years old) submitted to a 6-week drop jump plyometric training program, the post-training results pointed to significant increases in countermovement jump values either by the group who performed 50-cm height drop jumps or by the group who started with 100-cm height (37). These groups significantly differed from the control group on the assessed variable. The control group did not show any statistically significant change on the countermovement jump. The outcomes achieved by the experimental groups are similar to those identified in the present investigation, and we agree with the authors' statement that “plyometric training employing drop jumps could be a powerful tool for improving jumping performance even in high level athletes” (37, pp. 163).

Significant increases were observed in squat jump, countermovement jump, and mechanical power in young male basketball players (n = 19; 13-14 years old) previously submitted to an 8-week plyometric training program (43). These data are similar to those obtained in our study and, along with the results of Santos and colleagues (43), proved the efficacy of this training methodology in the improvement of young basketball players' explosive strength. As suggested by Santos and colleagues (43), it is our belief that the progress achieved in such a study can be attributed to the athletes' great adhesion to the training proposals. This understanding clearly leads us to the motivation issues, which play a key role in vertical jump performance (41). In fact, plyometrics (and particularly the depth jumps) can be seen as a motivating method, as stated by the subjects studied by Clutch and colleagues (11), because of the structural variation on the usual training design. It is our conviction that motivation was essential to the success obtained in the present study given the originality of the applied exercises and their diversity and the feeling experienced by the athletes about the improvement of their own motor availability for the basketball game.

Another factor that may have contributed to the successful training program was the way in which the plyometric component intensity was selected, using Chu's progressing scale (8). Because the gradual progression of the load is a main characteristic of this scale, it has been referred to as essential in terms of quality when working with adolescents (18). The design of this training program took into account the fact that some plyometric exercises, such as depth jumps, depend on high-intensity movement. Therefore, the drop height is a key factor when prescribing this type of exercise. According to the literature a 40-cm drop height was selected as the most appropriate when training young athletes (34,35), with clear results in the vertical jump enhancement (2,6,24).

Explosive strength improvements evidenced in the present study may also be attributed to the adoption of adequate recovery periods enabling a complete regeneration of the phosphagen stores (42). This way, the muscular fatigue was avoided, which, being a technique deterioration factor, reduces the required training quality (1,10). The recovery following depth jumps must consist of 15 to 30 seconds and 3 to 4 minutes of rest, respectively, between repetitions and sets (1). In fact, a 15-second rest proved to be an adequate recovery period to perform consistent depth jumps in a study with recreational strength trainers (42). However, the authors state the need for longer recovery periods, which may range from 30 to 60 seconds, depending on the number of jumps. Although identical recovery periods were prescribed in the present investigation, we think that exercise intensity is determinant in the adoption of recovery periods, and as intensity of exercises enhances, so should the recovery periods between sets and exercises. In this way, and using Chu's intensity scale, the adoption of recovery periods in our study in a range of 15 to 90 seconds and 1 to 4 minutes, respectively, between exercises and sets may have undoubtedly contributed to an optimized work, which was reflected in the outcomes.

Concerning the upper body, we have chosen the medicine ball throw exercise as the most adjusted to the training with adolescents. This kind of exercise is the best for the development of upper-body plyometrics (23). Furthermore, the choice of a 3-kg ball was consistent with the opinion expressed by Gambetta in a roundtable discussion about plyometric training (23). These aspects were determinant to the rate progression of our subjects (14.9%).

A program of this nature is also a strong contribution to the motor learning domains with positive repercussions on upcoming motor behaviors. This idea fits Faigenbaum's understanding (17, p. 13) when he states, “[P]erhaps it is not surprising to note that the best athletes in the world learn how to perform complex skills during childhood and adolescence.” This motor learning conception is especially important when teaching plyometric exercises to young athletes because one is “trying to teach the neuromuscular system how to perform relatively complex movements more efficiently” (9, p. 26).

It is worth enhancing the absence of injuries during the experimental program application. Although it is not the aim of this investigation, this fact is also an advantage achieved by our program, confirming that plyometric training with youngsters can reduce injury risk (9).

We also know that growth and maturation have positive effects on the improvement of adolescents' male strength levels. Explosive strength in a 13 year old is positively related to biological maturation even after the control of chronological age, stature, and body mass variation (3). At the beginning of the present study, both groups were similar in age, weight, and height values and they were equally assigned to III and IV Tanner's maturation stages. Nevertheless, the control group decreased with statistical significance in the values of vertical jump, whereas the experimental group significantly increased this variable. From this point of view and facing the distinct behavior of the analyzing groups, we can state that growth and maturational factors did not determine differences in the subjects' explosive strength levels throughout 10 weeks of study. Despite everything, we are conscious of the relevance of growth and maturational factors on the development process of adolescent males' muscular strength.

Based on the ideas and outcomes previously presented it seems clear and strongly sustainable that plyometric training has positive effects on upper- and lower-body explosive strength levels, mainly in the improvement of vertical jump, which is essential for basketball performance.

Several authors suggest that it is possible to retain previously achieved strength levels during short-term detraining periods. In fact, strength performance can in general be maintained over 4 weeks of inactivity (38). In other words, short-term detraining periods are adequate to retain previously achieved strength levels and do not seem to affect in a significant way the vertical jump (21). However, the maintenance of training intensity seems to be a key factor to the retention of adaptations throughout reduced training periods independently of its volume and frequency reduction (39). Our results fit these perspectives because both groups (detraining and reduced training) managed to retain during 4 weeks the levels obtained on the previous training phase.

After a 4-week detraining period, stability on the vertical jump height in prepubertal subjects was observed (19). Male basketball players who previously submitted to 4-week electromyostimulation training showed squat jump stability and significant increases in countermovement jump in the subsequent 4 weeks of standardized basketball training alone (36). Our results equally reveal squat and countermovement jump stability for the detraining group and sustain the idea of muscular attitude maintenance, which is a result of the standardized basketball training (36).

In a more extensive way, Santos and colleagues (43) noted stability on squat jump, countermovement jump, and mechanical power values in young basketball players assessed over 4 weeks of detraining and reduced training. Furthermore, the authors observed a similarity between detraining and reduced training groups at the end of the evaluation period. These results are identical to those of the present study and, once again, according to the authors' conclusions we can state that both a reduced training program and a detraining situation indistinctly contribute to the maintenance of explosive strength levels. Thus, these results highlight the unique role that basketball-specific training seems to play on the sustainability and maintenance of sport performance.

Extending the detraining period up to 8 weeks, Faigenbaum et al. (19) observed a stability of vertical jump height. Similarly, 8-week detraining showed stability on squat jump, countermovement jump, and depth jump indicators in prepubertal football players following the application of a 10-week plyometric training (14). These authors suggest that the maintenance of athletic performance may be explained by the extension of specific football training and by the short-term detraining period. Our results also show stability on squat jump, countermovement jump, and depth jump values for the detraining group. In this context, we agree with the statements presented by Diallo et al. (14), and it is our conviction that our outcomes can be clarified by the explosive nature of the basketball game, which, together with a short-term period of specific stimulus absence, will result in the maintenance of explosive performance levels. However, we believe that the quality of the initial plyometric program provided a solid background for the preservation of vertical jump values and the medicine ball throw distance.

In another investigation, it was observed that the vertical jump height and the basketball chest pass distance regressed to pre-training levels at the end of 12-week detraining (30). According to the authors, this regression is probably a result of neural deterioration with values similar to the regression rate of other training modalities. These data differ from ours possibly because of the maturational characteristics and the sport practice involvement levels displayed by the subjects of the 2 samples. In fact, our subjects were in III and IV Tanner maturational stages, in contrast to I and II Tanner stages revealed by the subjects in the study carried out by Ingle and colleagues (30). Also, our athletes are basketball players who simply ceased the strength training and continued basketball regular practice, whereas active individuals, students from a basic school, composed the sample on the study by Ingle and colleagues (30). We think that the basketball-sustained practice with high explosive levels was responsible for the explosive strength maintenance in our subjects over the detraining period. We also believe that this procedure may have avoided neural deterioration, which is responsible for strength levels regression (30).

Hoffman and collaborators (29) examined the responses of various performance tests related to strength, speed, endurance, and quickness during a Division I basketball season. The subjects ceased the strength training process after a 5-week in-season resistance training program, carrying on periodical assessment at the 10th and 20th detraining weeks. Considering the achieved results (significant decreases and stability on vertical jump, respectively, at the 10th and 20th week of detraining), the authors concluded that it is possible for an athlete to retain most pre-season conditioning levels through a college basketball season. In general, our results are in agreement with the conclusions obtained by Hoffman and collaborators (29) because the previously achieved explosive strength levels remain constant throughout the 16-week in-season detraining.

In brief, the detraining studies available in literature refer to both the maintenance and the reduction of previously achieved explosive strength levels. However, there is an obvious scarcity of studies on the influence of maintenance programs on explosive strength levels stability. To our knowledge, the study by Santos and colleagues (43) is the only one referring to stability on squat jump, countermovement jump, and mechanical power values in young male basketball players subsequent to a 4-week reduced training program. In the present study and in a similar time period the reduced training group maintained the previously obtained explosive strength levels. Moreover, a detailed analysis on absolute values evolution highlights that a once-weekly high-intensity plyometric training workout increased the assessed variables values in a 16-week period. In the same way, the inclusion of 1 workout every 2 weeks consisting of several vertical and horizontal jumping exercises (100-150 jumps) performed as explosively as possible enhanced the vertical jump height on squat and countermovement jump in female basketball players during the competitive season (27).

We are convinced that beyond the reasons previously expressed and subjacent to our results is the fact that basketball has a strong explosive component allowing for the maintenance of strength levels by the previous application of a specific training program. This is also the understanding of Hoffman and collaborators (29) when they state that it is common for college basketball teams to participate in short-term strength training programs that make coaches believe that high-intensity basketball practice alone is sufficient to maintain previously achieved strength levels.

However, the extent of sustainability and/or decrease on explosive strength values during detraining depends on the volume and intensity load, on the preceding training program, and on the type of physical activity performed during detraining and its temporal duration (33). Based on these authors' understanding, it is also our conviction that the conjugation of the effects of the previous strength training with the quality of the performed physical activity (in this case, the basketball regular practice) may have contributed to the outcomes identified in our detraining group. Another explanation for this retention on the previously achieved gains is probably explained by the so-called muscular memory (45). The authors studied the effects of heavy-resistance strength training followed by detraining and retraining periods in women experienced in strength training and observed significant increases in maximal dynamic strength. During the 30 to 32 detraining weeks, these values significantly decreased but remained higher than pre-training levels. The subjects retrained 6 weeks later, enhancing maximal dynamic strength values, which became similar to post-training levels. The investigators believe that their results display a retention effect, which allows previously heavy-resistance-trained women to increase maximal dynamic strength in a relatively short retraining period. This fact may be explained by the muscular memory phenomenon, which makes it possible that such aspects as increased neural activation and/or muscular hypertrophy be retained during a detraining period (45). The extrapolation to our results also makes it possible to identify the muscular memory phenomenon as responsible for the maintenance of strength values obtained in the present investigation-that is, when previously and specifically stimulated, the muscles used in strength training will “record” in their memory the adaptations produced and later reactivated throughout sports preparation. In the specific case of our study, the strength maintenance program (reduced training group) and the basketball regular practice (detraining group) promoted a permanent demand to that muscular memory with visible effects both on stability and on increments of explosive strength values.

The literature highlights the fact that prepubertal and early pubertal boys do not appear to sustain training-induced strength gains during detraining; likewise, a once-weekly maintenance-training program is not effective in preserving prior strength gains (4). In the same way, training-induced strength gains in preadolescents are impermanent and tend to regress toward untrained control group values during the detraining period, being probable that similar findings would be observed in adolescents (16). These understandings are opposed to our results. However, because our athletes are in III and IV Tanner stages, we do not neglect the important role that growth and maturation may have played on explosive levels maintenance identified in our study groups (detraining, reduced training, and control). Moreover, some authors report that very importance on strength levels evaluation in detraining groups (14,30).

We are convinced that on the basis of our results and beyond the reasons previously expressed basketball is a sport with a strong explosive component, allowing for the maintenance of strength levels obtained by the previous application of specific training programs. This is also the opinion stated by Hoffman and collaborators (29), who concluded that it is usual for college basketball teams to participate in a short-term strength-training program. At the end of this period coaches assume that high-intensity basketball practice by itself is sufficient to maintain the previously achieved strength levels.

In conclusion, the plyometric training program has proved efficient for upper- and lower-body explosive strength improvement in adolescent male basketball players. However, medium-term detraining and reduced training periods allow the retention, in a similar way, of explosive strength gains previously achieved.

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Practical Applications

The present study showed that the 10-week in-season plyometric training significantly increased upper- and lower-body explosive strength in adolescent male basketball players. These results support the specificity concept. Furthermore, and if it is correctly designed and competently supervised, this training program will not carry on an extra overload in the adolescent muscular-skeletal development as proved by the zero injury rate during the program application. However, despite the strong component of jumps inherent to basketball practice, this team sport has not by itself the power to increase the explosivity levels in young basketball players, as shown by the outcomes achieved by the control group (which only performed basketball). In this sense, our suggestion points out the possibility for the coaches to safely choose a varied, progressive plyometric program, with each workout lasting 30 minutes.

During the following 16 weeks of detraining/reduced training, the previously achieved explosive levels were retained. The fact that basketball is a sport with a strong explosive component allows for the maintenance of strength levels obtained by the previous application of specific training programs. Nevertheless, simultaneous to basketball practice, the coach's option for the pursuit of a plyometric training program in a reduced version allows the athletes not only the sustainability of the previously achieved gains, but also the possibility to obtain additional gains-namely, in the countermovement jump, the depth jump, and the medicine ball throw. Thus, depending on training time management, the coach may choose either the dropout of specific strength training stimulus or the adoption of a maintenance training program, ensuring that whatever the option, the previously achieved explosivity levels will be maintained. However, the coach may be conscious of the fact that the absence of a plyometric training program throughout the basketball season with young athletes implies a lower-body explosive strength decrease; subsequently, the nonsignificant gains obtained with the regular basketball practice are at pre-training levels. Therefore, young athletes' coaches are recommended to insert plyometric training in their training routines because they know that the adoption of subsequent detraining and/or reduced training periods indistinctly contributes to the strength levels maintenance.

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Acknowledgments

We would like to thank all the athletes who participated as subjects in the study and their head coach, Carlos Von Hafe, and assistant coach, Rui Sousa. The authors also thank Coach José Luís Gonçalves for his contribution and Denisa Mendonça, PhD, for providing statistical support. We also acknowledge Grupo Desportivo de Basquete de Leça for providing equipment support.

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    Keywords:

    vertical jump; medicine ball throw; youngsters

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