Basketball is a multifaceted team sport that requires a well-developed anaerobic fitness to be played successfully (25).
Many authors have suggested that explosive power in the form of vertical and horizontal jumps is an important characteristic for elite basketball players (16,21,34). Furthermore, vertical jump (VJ) ability has been reported to be related to elite college-players' playing time (17).
This belief was shown to be shared by the National Basketball Association strength and conditioning coaches who reported an extensive use of plyometric exercises to improve explosive-power performance in elite-level professional basketball players (17,30).
Plyometric training has been proposed for the development of explosive-power performance and specifically for the improvement of VJ ability (2,23). However, only few papers addressed the use of plyometric protocols on explosive-power performance in men's basketball (24,26). Furthermore, the published papers only addressed young basketball players selectively using drop jumps as training exercises (24,26). Additionally, no information was provided regarding the effect of plyometric training on horizontal-jump performance, an ability that has been associated with running acceleration performance in team sports (9).
Luebbers et al. (22) showed that a short-term plyometric training protocol resulted in significant enhancements in VJ performance in physically active college-aged men. Recently, the Luebbers et al. (22) protocol was reported to positively affect VJ performance in well-trained soccer players (19). However, to the best of this study authors' knowledge, no information is available on the effect of this popular plyometric training protocol in well-trained basketball players.
Recently, weighted-vest jumping has shown to acutely enhance jump performance in athletic populations (8,32). However, no training studies were conducted to test the added effect of weighted plyometric exercises on jump performance (i.e., vertical and horizontal) in basketball players (34). Information in this regard may result in interest in optimizing training prescription to strength conditioning professionals that deal with basketball (34).
As a result of the above reasoning, the aims of this study were to examine (a) the effect of a popular short-term plyometric training (22) on vertical and horizontal-jump performances in experienced basketball players; and (b) the possible additive effect of weighted vests on jump performance provided in the Luebbert et al. (22) protocol.
As a working hypothesis, it was assumed that loaded plyometrics would add benefit to unloaded training in basketball players (19).
Experimental Approach to the Problem
Recently, Ziv and Lidor (34) suggested the use of plyometrics to develop jump ability in basketball players. In this study, the development of jumping ability in basketball players was achieved using the plyometric training protocol provided by Luebbers et al. (22) (Table 1). This protocol involves a periodized use of vertical and horizontal jumps that proved to increase vertical (i.e., VJs) and horizontal (i.e., short sprints and broad jumps) explosive power in healthy individuals (19,22).
To examine the additive effect of loaded plyometrics on jump performance, a randomly selected group of players performed the Luebbers et al. (22) protocol using weighted vests of 10-11% of body mass (3,6,11,15) (see Figure 1). The training-intervention duration considered in this study was of 10 weeks according to the typical preseason strength and conditioning programs usually adopted by elite-level basketball teams (30). Furthermore, longer and less aggressive plyometric protocols showed to provide immediate posttraining-intervention improvements in explosive-power performance (22).
To examine the possible time per treatment effects on jumping performance of plyometric training (22) in male basketball players, a randomized controlled design was used. Training outcomes were assumed as VJ height (4) and distance achieved during 5 horizontal jumps (5JTs) (9). Vertical- and horizontal-jump performances have been reported to be relevant performance variables in basketball (14,17,24,26,30,34).
Twenty-seven elite male basketball players (Tunisian First Professional Division; mean: 23.61 ± 0.96 years) who trained 12-15 h·wk−1 participated in this study. Players' anthropometric characteristics (n = 27) are presented in Table 2.
Players were randomly assigned to 2 experimental groups and 1 control group (CG; n = 9 each). The experimental groups performed the plyometric training either with plyometric (loaded plyometric group [LPG]) or without plyometric (PG) loads. The CG did not perform any other training intervention than basketball skill development during the period of the investigation. At the time of the study, players possessed 12.4 ± 3.50 years of basketball experience. The training intervention took place at the beginning of the training season as precompetitive preparation. All players were not involved in any specific training session but were active during the preceding 4 weeks. During the training intervention, all players did not participate in any other exercise activity other than basketball training and refrained from strength training. Basketball training at the time of the investigation consisted mainly of individual and team skills development and was implemented in the form of daily sessions 6 times a week (∼90 minutes). A competitive game was played during each weekend. Written informed consent for all players involved in this investigation was obtained before the commencement of the study. The study was reviewed and approved by the Committee on Research for the Medical Sciences of the University of Tunis before all the procedures began.
Players' body mass was measured to the nearest 0.1 kg using an electronic scale (Seca, Hamburg, Germany). Standing heights were measured using a wall stadiometer (Model GPM, Seritex, Inc, Carlstadt, NJ, USA). All measurements were recorded by the same well-trained examiner, using standard protocols. After familiarization with the testing procedures undertaken during plyometric training, each player was instructed and verbally encouraged to give a maximal effort during all tests. Measurements were taken before and 48 hours after completing the 10-week training-study program. The outcome measurements were taken by assessors who were blind to group allocation and who had no involvement in the recruitment, the randomization, and the training of participants.
Basketball players completed the jump test sessions after a 10-minute warm-up consisting of low-intensity running, striding, and 5 minutes of coordination movements. Thereafter, a 5-minute specific warm-up was performed using exercises mimicking and priming test movements. Three minutes of recovery separated the warm-up from the tests.
Vertical jump performance was assessed using squat (SJ) and countermovement (CMJ) jumps according to the procedures suggested by Bosco et al. (4). Jumping height was assessed using an infrared photocell mat connected to a digital computer (Optojump System, Microgate SARL, Bolzano, Italy). All VJs were performed with hands held on the hips and attaining 90° knee flexion at the start of the push-off phase. Players performed 3 trials of each jump, and the best of each jump mode was considered for analysis. According to Bosco et al. (4,5), muscle elastic recoil was assessed using the CMJ-SJ difference.
The 5JT consists of 5 consecutive strides with joined feet position at the start and end of the jumps (9). From the starting joined feet position, the participant was not allowed to perform any back step with any foot; rather, he had to directly jump to the front with a leg of his choice. After the first 4 strides, that is, alternating left and right feet 2 times each, the player had to perform the last stride and finish the test with joined feet again. If ever the player fell back at the reception of the last stride, the test was reperformed. The 5JT performance was measured with a tape ruler from the front edge of the player's feet at the starting position to the rear edge of the feet at the final position. The assessor at landing had to focus on the last stride of the player to exactly determine the last footprint on the grass, because the players could not always stay on their feet on landing. The starting position was settled on a fixed point.
All subjects were tested before and at the completion of the 10-weeks' training period. Familiarization with the procedure employed in this study took place during the 2 weeks preceding the training study. Training was completed twice a week during the first 3 weeks and 3 times a week for the last 7 weeks (ca. 90 minutes per training session). Recovery times between repetitions and sets were 15-40 seconds and 2-3 minutes, respectively. To favor training supervision, each group was in charge of a professional strength and conditioning coach.
Mean, SDs, and SEMs (SEM = SD/n1/2) were calculated for all the dependent variables. Values are expressed as mean ± SEMs. Percentage differences were calculated using the formula ([post − pre]/pre × 100). The magnitude effect that represents the difference between means of the dependent variables was calculated using the formula: magnitude = postmean − premean.
Pre to postcomparisons were performed using 2-way analysis of variance designs. If statistically significant F-values were detected, a Newman-Keuls post hoc test was used.
Statistical significance was fixed at the p ≤ 0.05 level. The dependent variables were SJ, CMJ, and 5JT performance. The intraclass correlation coefficient for the variables used as training outcome ranged from 0.89 to 0.96 (33). Before the commencement of the training intervention, a pilot study was performed to develop power calculations to guide in sample-size determination. This suggested a minimum of 6 subjects per group allocation for a power of 0.80 (10).
Pre to posttraining effects on performance variables are reported in Table 3. After 10-week training, only the PG and LPG significantly improved their VJ performance (SJ and CMJ, p < 0.05). The SJ performance was significantly improved by 5.8 and 9.9% (i.e., 3.73 and 2.2 cm), in PG and LPG, respectively (p < 0.05).
The CMJ performance was significantly (p < 0.05) enhanced by 12.2 and 7% (i.e., 5.34 and 3.1 cm), in LPG and PG, respectively (Table 4). Performance gains in SJ and CMJ were significantly higher in PLG compared with in PG (p < 0.05). The CMJ-SJ value significantly improved in LPG and PG (Table 3) by 27.4 and 59%, respectively (p < 0.01).
Improvements in 5JT performance were significantly greater in the LPG than in PG (p < 0.05, Table 3). The magnitudes of improvements for the 5JT performance were 5.6% (i.e., 66 cm) and 7.5% (i.e., 91 cm) for PG and LPG, respectively (p < 0.001). No significant changes were observed for the CG in any of the considered performance variables (Table 4).
The main finding of this study was the improvement of either vertical- and horizontal-jump performance in basketball players as a consequence of a multipurpose plyometric training intervention (i.e., vertical- and horizontal-jump exercises) (22). This loaded (i.e., 10-11% of body mass) plyometric training showed to provide a further advantage over the standard (i.e., body mass) condition (22). This confirmed our work hypothesis giving evidence that loads (i.e., ca. 10% of body mass) added to dynamic exercise may provide training besides acute benefits over explosive-power performance (8,32).
Vertical jump is a frequent act performed by basketball players as part of defensive (e.g., blocking, rebounding, and stealing) and offensive (e.g., passing, rebounding, and shooting) maneuvers during training and competition (34). A number of observational studies have been performed to gain information on the VJ performance of basketball players (34). Comparison with published papers showed that in this study, CMJ and SJ performances were within the range of those reported for male elite level basketball players (i.e., 40.1 ± 4-43.9 ± 4.0 and 39.8 ± 3.7-41.5 ± 3.0 cm, respectively) (1,13). This supports the external validity of this study research design (31).
Longitudinal observational studies that addressed the VJ performance as a consequence of participation in men's basketball training and competitions showed conflicting results (17,18). Hunter et al. (18) reported no VJ variation in college basketball players observed during 4 competitive seasons. In another study (17), a 4.6-cm increase of VJ performance in varsity players from freshman to senior years was reported (i.e., 4 seasons). This study's findings showed that the short-term plyometric protocol (i.e., 10 weeks) used induced absolute improvement in VJ expected as a consequence of long-term basketball training and competitions (17). Given the supposed importance of plyometric training (34) in basketball, this study's findings support the use of the Leubbers et al. (22) protocol with male basketball players.
Similarly to other studies, plyometric training showed to be effective in improving VJ performance in a jump-accustomed population of basketball players (24,26). Specifically, the magnitude of the improvements experienced by the PG was within the range of those reported in the international scientific literature in the athletic population (i.e., 4.7-8.9%) (23). Interestingly, the loaded plyometric training showed to produce VJ improvements that exceeded the upper end of the improvements range (i.e., 10-12%) reported by Markovic et al. (23).
However, this study's findings showed the likelihood of a dose-response effect of plyometric training on VJ performance. Indeed, by wearing weighted vests, players were able to show further improvements in jumping performance. This extended the descriptive studies by Burkett et al. (8) and Thompsen et al. (32) that showed acute enhancements of VJ performance in subjects wearing weighted vests during warm-up.
In the Burkett et al. (8) study, the use of added loads similar to those in this investigation (i.e., 10% body mass) has shown a significant 2.7% improvement on VJ performance in college football players. This acute VJ improvement was remarkably lower than the training response found with this study intervention (i.e., 10-12% improvement). Interestingly, the acute effect of weighted movements seems to be magnified by the use of body mass increments in the range of 2% (12). As a consequence of this and other study findings, it could be speculated that the progressive use of added loads during the training session may prime (i.e., acute effects) and develop VJ performance in team-sport players (8,12,32). Training studies investigating this interesting issue are warranted to provide evidence.
The chronic wearing (i.e., morning to evening) of weighted vests (i.e., ∼11% body mass) has been reported to sort a positive effect on explosive-power performance in well-trained track and field athletes after a 3-week intervention (3,7). In a noncontrolled training study, the hypergravitational condition induced improvements in VJ performance quite higher than those achieved by the basketball players of this study (24 vs. 5-12% improvement, respectively) (5). However, improvements within the range of this study findings (i.e., 5-10% p < 0.05) were reported by Bosco et al. (4) in international-level jumpers and throwers that experienced the hypergravity condition for 3 weeks in a controlled training study. This study's findings provided experimental evidence for the effectiveness of "temporary" hypergravity (i.e., only during plyometric exercises) intervention on jumping performance. This issue holds practical interest because more aggressive treatments (i.e., wearing the vest morning to evening) may have a limited practical application (3,7). Another issue of interest would be the cumulative (i.e. periodized) effect of plyometric training using progressive (i.e., switching from unloaded to loaded plyometrics) loading on team-sport players (20).
As expected, the plyometric protocols used in this study showed to provide a higher improvement magnitude on stretch-shortening activities such as CMJ and 5JT (23). Similar results were reported by Bobbert et al. (2) and Markovic et al. (23). Plyometric training consists of stretch-shortening cycle movements that involve a high-intensity eccentric contraction immediately before a rapid and powerful concentric contraction (2,23). It has been recently suggested that plyometric training is more effective in improving VJ performance in the slow stretch-shortening cycle jumps because it enhances the ability of subjects to use the elastic and neural benefits of the stretch-shortening cycle (23). This study supports these suggestions, because our results indicate that slow stretch-shortening cycle jumps (i.e., CMJ) are likely to benefit more from plyometric training than concentric jumps (i.e., SJ). Indeed, according to the study of Markovic (23), we observed that the gain obtained with CMJ was significantly greater than that obtained with SJ (p < 0.05) either in PG or in PLG. Considering the specificity of contraction-type followed during training, greater positive effects of plyometric training on the CMJ than on the SJ can be expected (23). The supposed reasons underpinning stretch-shortening performance enhancement as a consequence of plyometric training are reported to be variation in the muscle-tendinous ability to store elastic energy and stimulation of the myotatic reflex during the eccentric contraction before the upward movement (23,34). In this, the evidence for a training surface effect on selective plyometric training outcomes was reported by Impellizzeri et al. (19). Indeed, those authors reported that SJ performance enhanced more as a consequence of performing the Leubbers et al. protocol (22) on the sand compared with the grass condition (19).
In this study, the training interventions showed to positively affect the ability to store and successively use elastic energy in the muscle (i.e., CMJ) in the experimental groups. However, the documented improvement resulted independently from jumping training mode (i.e., loaded vs. unloaded jump training).
The 5JT was used to detect improvements in the use of the slow stretch-shortening cycle as a result of the plyometric training (27-29). Recently, the 5JT was proposed to evaluate lower-limb explosive power of athletes competing in team sports (9). Our findings indicate that the enhancements of VJs in the 2 experimental groups (i.e., PG and LPG) were accompanied by significant increases of the 5JT performance (+5.6 and 7.5% for PG and LPG, respectively). Although greater increases of VJ performances were observed in the LPG than in the PG condition, both groups produced comparable improvement in 5JT performance. This finding may suggest that wearing loaded vests during plyometric training may exert more additive effects on VJ.
The results of the present study provided evidence for the validity of the Luebbers et al. (22) protocol in enhancing vertical and horizontal jumping abilities in basketball players. The use of added loads during the Luebbers et al. (22) protocol showed selective effect on jumping ability (i.e., VJ performance).
Jumping higher than their counterpart is one of the desired goals of basketball players irrespective of playing position (34). Failing to incorporate explosive type training during the competitive season has been reported to impair explosive performance in basketball players (34). Furthermore, strength training failed to show any VJ improvements throughout the season (16). This study findings provided evidence that the Luebbers et al. (22) protocol may enhance VJ and 5JT during the preparation phase of the precompetitive basketball season. Adding loads of 10-11% of body mass in the form of weighted vests may further enhance VJ and 5JT gains in performance. Despite the experimental success of the weighted vests, caution should be exercised in training prescription when addressing young female basketball players (14). In the training setup, progression in loading is strongly encouraged to avoid injury occurrence.
We declare that the present work complies with the current laws of the country in which it was performed (Tunisia). Authors certify that they do not have a financial relationship with the organization that sponsored the research. The authors declare that they have no conflict of interest.
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