The concept of combined training has been initially suggested by Verkhoshanski and Tatyan (43), and it involves high-intensity strength and ballistic training combined in the same session. The effectiveness of a combined training is attributed to a mechanism so-called postactivation potentiation. Regarding this mechanism, the twitch torque, the rate of force development, and the ballistic performance increases, after electrical (33,35) or voluntary activation under isometric (14,18,35) and dynamic maximal or close to maximal contraction (11,17). On the other hand, postactivation potentiation has no effect on the maximal torque and the unloaded shortening velocity (16,35).
The increased motor neuron excitability (14,42) and augmentation in the Ca2+ kinetics and in the light myosin chain phosphorylation (12,30) are some causes for the existence of postactivation potentiation. Furthermore, it is influenced by several factors, such as the muscle fiber type (18), the performance level (17,31), the intensity (33), and the volume (3,11) of the resistance training, the exercise type, and the time interval between the activation and the performance test (22).
The presence of postactivation potentiation has been more extensively studied on jumps than sprints after a heavy resistance stimulus. Concerning jumps, the majority of studies verified the presence of postactivation potentiation (11,17,22,37) although in some cases this was not very clear (11). Regarding sprints, postactivation potentiation has been reported during cycling (38) and running (4,29) sprints. However, a recent study showed that a preceding heavy resistance strength training program or a series of countermovement jumps did not have any effect on running speed (RS ), and this was attributed to the lower applied load volume compared with previous studies.
Running speed improves with several types of training interventions, such as sprint training without external resistance, towing, overspeed (7,8), and specific plyometric (speed-bound) exercises (34). However, conflicting results have been reported for the effect of heavy resistance strength training on RS. There are relevant studies, which show no effect independently of the intensity of the strength training program (7,19,36), whereas a recent study reports a positive effect on RS (20). The absence of adaptations on RS after strength training has been attributed to learning factors (36), that is, the nervous system cannot learn to control the augmented muscle mass and strength to recruit the appropriate motor units for the running task to increase the RS. On the contrary, the positive effect of resistance training on RS (20) was attributed to the strength gain per se.
After a combined training program (CTP), with sprints after a heavy resistance strength training session, the 30-m RS increased, whereas the 10-m RS did not change. To our knowledge, there are no studies investigating the effect of a CTP on RS, by performing the running trials between the sets of the strength training program. Such a protocol design could possibly cause a more effective transfer of the strength gain to RS, possibly by improving all running phases and other explosive tasks such as jumping. There is evidence that supports this hypothesis. More specifically when jumps were performed among the strength resistance sets, an enhancement on jumping performance after the sets was observed (37).
In particular for jumping, intervention programs have a selective effect. Heavy resistance training basically increases squat jump but not countermovement and drop jump performance (24). Moreover, plyometric training (24,28) and high resistance combined with plyometric training increased all types of jumping, whereas high resistance combined with sprint training affects squat jump only (23). Considering maximal running performance as an intensive stretch-shortening cycle (10,26) like drop jump, it would be important to investigate the hypothesis if a CTP, with the running trials performed between the resistance sets, would affect all types of jumping performance. Moreover, according to our knowledge, there is no study investigating the effect of a combined resistance training program on power performance when stretch-shortening cycle tasks, such as spring, are performed between resistance sets.
Experimental Approach to the Problem
This study was designed to test if a combined high resistance training protocol with sprint trials between the sets improves the performance of young basketball players, and more specifically their strength level, 30-m sprint performance (acceleration phase and maximal RS), and jumping ability (squat, countermovement jump and drop jump). For this purpose, junior basketball players were assigned to 2 groups: the control (CON) group that performed only technical-tactical preparation and the CTP group that performed additionally, for 10 weeks the CTP, consisted of a high-intensity resistance training with maximal sprints performed after each set of the resistance program. All participants would be evaluated for their repetition maximum (1RM), RS (0-10 and 0-30 m) and jump height (squat jump, countermovement jump, and drop jump) before the CTP group starts training (Pre), at the fifth week of training (Post-5) and at the end of 10-week program training (Post-10). For familiarization purposes, participants learned to perform all tests, before the first evaluation.
Twenty-six healthy junior basketball players volunteered to participate in this study and were randomly assigned to either the CON or the CTP group. All participants played in the local junior basketball league and had no background in resistance or plyometric training (Table 1).
The experimental procedure was performed according to the ethic guidelines of the Aristotle University of Thessaloniki, Greece. All subjects were informed about the experiment and all possible risks associated with their participation. Before testing they filled out a medical history questionnaire and signed the informed consent document. Their parents were also invited before the intervention to be informed about the study and to give their written consent as well. A physician examined all participants and classified them to the fifth maturation stage, according to Tanner (39).
Both CTP and CON groups followed a preparatory training program for 4 weeks, 3 times per week, including training components that enhance endurance, endurance in strength, flexibility, and coordination. This training period served as a preparatory phase to prevent injuries (23) that could occur because of the high intensity of the program that the CTP group would follow. During the last week of this period, all subjects performed all tests to be familiarized to avoid any learning effects on their performance (9).
During the 10-week experimental period, the CON group performed only technical and tactical preparation and did not carry out any plyometric exercises or regular running training. In addition to the technical and tactical training, the CTP group performed 2 strength training sessions per week with a 2-day interval in between. More specifically, in the first 5 weeks the CTP group carried out 5 sets of 8RM half squat, and during the last 5 weeks, the intensity was increased to 5RM. The resistance was adjusted every week. During the training session of the CTP group, after each half squat set, one maximal 30-m sprint was performed (Table 2). A resting interval of 90 seconds was given before and after the sprint. Only the last sprint was performed immediately after the last weight lifting set. This was required to fulfill the experimental conditions for another study.
All participants had the same coach and during the training period followed a common technical training program, without participation in any competitive games.
The tests were carried out in a sport hall, with temperature 25-30°C. All subjects participated in familiarization sessions before their evaluation. They performed a general warming up program (10 minutes cycling on a MONARK™ cycling ergometer, Varberg, Sweden) and specific warming-up exercises. Afterward, they performed the 30-m sprint test, the jump tests, and 1RM half squat test at 90°.
The half squat was performed according to previous studies (4,23). Briefly, the Smith machine was used, with adjustable brackets, which forces the bar to travel over a predefined straight and vertical path. The participants stepped under the bar, in upright position, looking forward, and grasping firmly the bar with both hands to support its load upon their shoulders. They were instructed to flex their knees at 90°, with the trunk tilted slightly forward and the heels on contact with the ground. After reaching this position, they returned to the starting position. Knee angle was evaluated with a goniometer, and brackets were placed to prevent knee flexion above 90°. The position of the brackets was registered for each subject and was constant in the subsequent testing sessions.
1Repetition Maximum Estimation
Before testing, participants executed a specific warming up, including submaximal repetitions at intensities of 40-80% of their self-perceived 1RM. Afterward, each participant estimated according to his experience his 1RM. Starting 5% below the self-estimated 1RM load increased gradually by 2% after each successful trial. This procedure was repeated until the participants were not able to execute the full range of motion for the selected load. The interval between the repetitions was 5 minutes. For the final estimation of 1RM, 3-6 trials were required. All testing procedures were supervised and assessed according to the American College of Sports Medicine guidelines (2).
As specific warm-up, the athletes executed running trials of moderate intensity and finally 2 maximal sprints with 5 minutes interval between them. The evaluation started 5 minutes after the end of the warming up. Intervals included active recovery. Running speed was evaluated with 3 pairs of photocells and reflectors (TAG Heuer™, Oberursel, Germany) placed at shoulders height and connected with an electronic timer. To evaluate the 0- to 10-m and 0- to 30-m distances, pairs of photocells were positioned at the start, 10 m, and 30 m. The 0- to 10-m distance was selected as indicative of the initial acceleration ability. Sprints were executed from standing start position. Verbal encouragement was given during the maximal RS evaluation. The subjects performed 4 maximal trials with a 3-minute interval between them. The best trial was further processed.
Before evaluation subjects were warmed up with submaximal and a few maximal jumps of all tested types. The following jump types were executed: (a) Squat jump: The participant started from a stationary position with the knees flexed at 90° and jumped upward as high as possible. (b) Countermovement jump: The participant started from an upright standing position, performing a very fast downward movement flexing ankles, knees, and hip and immediately after jumping up off the ground. (c) Drop jump: The participant jumped from a 40-cm high bench and performed a maximal jump immediately after landing on the floor.
All jumps were performed barefoot, with the hands placed on the hips. The instructions were to jump as high as possible. Jump height was evaluated with the ErgoJump™ Boscosystem apparatus (Jyvaskyla, Finland).
Means and SEs of all dependent variables are presented. All dependent variables were analyzed using a 2-way analysis of variance (ANOVA) 2 × 3 statistical model consisted of the factor GROUP (2 levels: CTP and CON groups) and the repeated-measures factor TIME (3 levels: Pre, Post-5, and Post-10 weeks of training). Pairwise comparisons were assessed with post hoc tests. The level of significance was set at p ≤ 0.05. Test-retest measurements were assessed during familiarization and the intraclass correlation coefficient (ICC) for all dependent variables was calculated.
Results for Repetition Maximum
The ICC between the trials was r = 0.94. The 2-way ANOVA revealed a significant interaction effect (F(2,48) = 226.7, p < 0.01). There was no significant difference between groups for the measurement before the training onset. During the Post-5 and Post-10 measurement, the CTP group performed significantly better than the CON group (Figure 1). The CON group showed no significant difference between the 3 measurements along time. The subjects included in the CTP group increased their RM significantly after the fifth week compared to the pretraining values. Further statistically significant increase was observed after 5 weeks of additional training.
0- to 10-m and 0- to 30-m Sprint Times
The ICCs between the trials for 0-10 and 0-30 m were 0.90 and 0.93, respectively.
Regarding the initial phase of speed (0-10 m), a significant interaction effect was shown (F(2,48) = 8.47, p < 0.01). Post hoc analysis revealed no significant difference between groups before the onset of the training period; nevertheless, the measurements 5 and 10 weeks after training showed that the CTP group had significantly lower sprint times compared to the CON group (Figure 2). The subjects of the CON group did not differentiate their performance between measurements. This was not the case with the subjects of CTP group that performed better after 5 and 10 weeks of training compared to the pretraining values.
Regarding the performance for the 0- to 30-m distance, the 2-way ANOVA showed a similar to 0- to 10-m distance magnitude of interaction effect (F(2,48) = 10.8, p < 0.01). Pairwise post hoc comparisons revealed significant difference between the groups after training (Post-5 and Post-10), and this was not the case before training (Pre, Figure 2). No significant difference was observed between measurements of the CON group. The CTP group performed better after 5 and 10 weeks of training compared to the pretraining values and this difference was statistically significant. Furthermore, differences were significant between the 5th and 10th weeks of training for the CTP group.
The ICC between the trials for squat, countermovement, and drop jump was 0.94, 0.96, and 0.94, respectively. Results showed by all jump measures significant interactions between group and time of measure. Specifically, the F(2,48) values for squat, countermovement jump, and drop jump were 14.3, 23.4, and 35.2, respectively.
Regarding squat jump, analysis showed no significant difference between groups in the first test. On the contrary, between the 5th and 10th weeks of training the trained group performed significantly better than the CON group (Figure 3).
Between measurements, there was no significant difference in the CON group. The subjects of the CTP group performed significantly better after 5 and 10 weeks of training compared to the pretraining values. The difference between the 5th and 10th week squat jump performance was significant as well.
Similar results to the squat jump were presented for the countermovement and drop jumps as well (Figure 3).
The results obtained indicate that the 10-week strength training program combined with running sprint trials between the sets of the strength training had a positive effect on the performance of the young basketball players. Specifically, it caused an increase in their half squat RM, in RS and in jumping performance. The training effect for the CTP group reached the significance level already during the fifth week. No changes were observed in the CON group.
The behavior of the CTP group indicates that the applied training protocol can increase the strength even within 5 weeks. Generally speaking, the strength can increase even after 1 week of resistance training and such adaptations are attributed purely to neuronal factors (6). However, the results obtained after the 5 and 10 weeks could be attributed to both neuronal and muscular factors (15), but it was beyond our scope to further analyze which factor contributed more and to what extent.
The effect of combined strength training programs on RS has been also previously documented (23). The effectiveness of such a program was attributed to postactivation potentiation because the RS program was performed 10 minutes after the strength program. However, in the mentioned study, RS increased for the 0-30 m and not for the 0- to 10-m sprint distance. In the present study, improvement in 0- to 10-m distance was evident as well. One possible explanation for this is that a more direct transfer of the strength gain to RS could occur when sprints are performed after each strength training set. This assumption could be supported by the concept that strength gain per se cannot be transferred to RS (36). Another explanation could be a possible facilitation on RS that occurs because of the postactivation potentiation effect after each set. Fatigue and facilitation coexist during training (32), and in our case, the facilitation could be caused by postactivation potentiation. It has been documented that RS is not affected immediately after a complete a heavy resistance strength training set because of fatigue, but it is facilitated 5 minutes after (4). Although there is no information for the effect of the postactivation potentiation on RS using intervals between 0 and 5 minutes, it seems that the 3-minute interval after resistance set of the present study could be possibly appropriate for postactivation potentiation on RS. This could be supported by the half resynthesis time for phosphocreatine that is approximately 30 seconds (40). Nonetheless, further studies are required to determine the optimal rest interval.
Concerning jumps, studies related to the effect of training on jumping performance have shown that strength training mainly increases squat jump height (24,25), whereas plyometrics (24,28) and resistance training programs combined with jumps, improves all types of jumping (13,41). An explanation for these differences is that pure resistance training increases the tendon stiffness, whereas plyometrics increase the overall joint stiffness (24). A combined training including resistance and jumping exercises affected the joint stiffness and improved all types of jumping as well (41). Recent studies (21,24,27,28,41) support the previously mentioned results, reporting that the optimal effect of a stretch-shortening cycle such as countermovement and drop jumps depends mainly on the active stiffness (part of joint stiffness), which contributes to a more effective the transfer of the stored elastic energy. The applied CTP in the present study merges strength and stretch-shortening cycle performance, as it happens in conventional combined programs with weights and plyometric jumps. This concept is based on the fact that sprint is actually a continuous, very intense stretch-shortening cycle, which requires high muscle activation, even higher than maximal isometric contractions (10,26). This could give another explanation for the improvement in jump height in the present study.
In another heavy resistance strength training combined with sprints, only the squat jump height increased (23). The difference in effectiveness compared to the present study could be attributed to the different applied training protocols. Specifically in the current study, the sprints were performed immediately after the resistance sets and not at the end of the strength training session. It seems that the current applied protocol is more favorable for transfer in strength gain on RS; however, more studies with direct comparisons between the training protocols are required for a clear conclusion.
The effect of the present CTP appeared after 5 weeks. Relevant studies have reported that a period of 4-6 weeks (1,44) is required for jumping enhancement after plyometric training, whereas the respective period for RS after sprint training is 5 weeks (5). From this point of view, it seems that the applied combined program was sufficient to cause the adequate adaptations on both RS and jumping performance within the first 5 weeks of its application.
The results of this study support that high resistance half squat training combined with running sprints between the sets can enhance half squat RM, 10- to 30-m RS, and all types of jumps in young male basketball players with no former experience in resistance or plyometric training. Coaches using such training programs in young basketball players may expect adaptations that affect positively both strength and power in a relative short period of 5 weeks. This is important to know for the training planning and especially when the preparation period is short. Further studies may clarify if such adaptations are present in high-level performance athletes as well, and if the suggested training protocol is superior in comparison to others.
The authors would like to thank all players for their decision to participate in this study.
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