Male collegiate volleyball players' depth jump biomechanical adaptations to eight-week complex-contrast training

Although complex-contrast training (CCT) is widely used to improve depth jump performance in volleyball players, the effects of CCT on depth jump biomechanics are unclear. Thus, this study aimed to analyze CCT's effects on depth jump biomechanics in volleyball players and to identify biomechanical factors that influence performance. Nineteen male collegiate volleyball players were randomly assigned to an experimental group (EXP: n = 9) or a control group (CON: n = 10). EXP underwent 8 weeks of twice-weekly CCT, while both groups completed three times weekly volleyball technical training. All participants' depth jump performance and biomechanical characteristics were assessed during the braking and propulsion phases using motion capture systems and force platforms at three time points: pre-intervention and after 4 and 8 weeks of CCT. Repeated-measures ANOVA showed that the interaction effects of time × group were not significant for all variables. For variables with significant main effects, further post hoc comparisons revealed that, in the EXP, jump height (JH: 0.510 ± 0.024 m vs. 0.560 ± 0.042 m, p = 0.013, Δ = 9.911% [95% CI: 3.266% to 16.557%]), peak propulsive velocity (PPV: 3.136 ± 0.089 m/s vs. 3.303 ± 0.154 m/s, p = 0.009, Δ = 5.341% [95% CI: 2.019% to 8.662%]), energy release (ERE: 8.755 ± 0.375 J/kg vs. 9.604 ± 0.725 J/kg, p = 0.019, Δ = 9.839% [95% CI: 2.830% to 16.849%]), and net energy release (NERE: 3.398 ± 0.709 J/kg vs. 3.907 ± 0.610 J/kg, p = 0.021, Δ = 17.548% [95% CI: 2.318% to 32.778%]) significantly increased from pre- to posttest. Furthermore, posttest values of JH (EXP: 0.560 ± 0.042 m vs. CON: 0.520 ± 0.033 m, p = 0.029) and NERE (EXP: 3.907 ± 0.610 J/kg vs. CON: 3.150 ± 0.614 J/kg, p = 0.015) were significantly higher in EXP than in CON. The results indicated that 8 weeks of CCT improved biomechanical variables of the depth jump, including JH, PPV, ERE, and NERE, in male collegiate volleyball players, while variables related to the braking phase were largely unchanged. Although post-test differences between groups were observed for key performance-related indicators, these findings should be interpreted with caution due to the absence of a significant time × group interaction and may reflect limited statistical power. Overall, this study provides preliminary evidence for the potential benefits of CCT on certain biomechanical outcomes, although further investigation with larger samples is needed to confirm and extend these findings.