Effects of jump exercises with and without stretch-shortening cycle actions on components of physical fitness in prepubertal male soccer players

Objective: This study examined the effects of 8 weeks stretch-shortening-cycle-based (SSC-based) versus non-SSC-based jump exercises on physical fitness in prepubertal male soccer players. Methods: Twenty-six participants were randomly assigned to either a SSC-based using countermovement-jump (CMJG; n=13) or a non-SSC-based jump group using squat-jump (SJG; n=13). Pre- and post-training, tests were conducted to assess measures of muscle power (countermovement-jump, reactive-strength-index), speed (5-m, 20-m), change-of-direction (CoD), and sport-specific performance (maximal-kicking-distance). To establish the effect of the interventions on the dependent variables, a 2 (group: CMJG and SJG) × 2 (time: pre, post) ANOVA with repeated measures was determined for each parameter. Results: Findings demonstrated a main effect of time for countermovement-jump, reactive-strength-index, and maximal-kicking-distance (p<0.05, effect size [ES]=0.56-0.71). Group × time interactions were identified for (5-m, 20-m, and reactive-strength-index (p<0.05, ES=0.59-0.64) in favor of CMJG. Particularly, pre-post performance improvements have been observed for 5-m (∆1.6%; p=0.04; ES=0.54) and 20-m (∆5.3%; p<0.01; ES=1.00) in the CMJG. For SJG, 5-m (∆-5.5%; p=0.01; ES=-1.12) and 20-m (∆-3.7%; p=0.01; ES=-0.82) pre-post performance declines were observed. Regarding reactive strength index, pre-post improvement was noted for CMJG only (∆-40.1%; p<0.01; ES=3.7). In addition, a tendency toward a group × time interaction was found for CoD (p=0.06, ES=0.54) with a performance decrement for SJG (∆-6.0%; p<0.01; ES=-1.8) and no pre-post changes for CMJG (∆0.15%; p>0.05; ES=0.05). Conclusion: Overall, jump exercises which utilise the SSC seem to be more effective in improving measures of speed and muscle power performance in young athletes. However, jump exercises that do not involve the SSC appear to negatively affect CoD performance in young athletes.