Influence of Repeated-Sprint Bout Duration in Sprint Interval Training Intervention on Physical Performance Adaptations of Young Volleyball Players.

The objective of this study was to examine the effects of repeated-sprint training (RST) with varying bout durations on the physical fitness adaptations of young male volleyball players. Forty athletes were randomly allocated to one of three intervention groups performing RST with varying bout durations and similar repetition volumes, all executed at maximal effort. The 3-sec group (n = 10) completed two sets of 30 bouts, the 6-sec group (n = 10) performed two sets of 15 bouts, and the 9-sec group (n = 10) carried out two sets of 10 bouts, each adhering to a 1:3 work to rest ratio. An active control group (n = 10) engaged solely in regular volleyball training without the RST intervention. Physical fitness measures-including countermovement vertical jump (CMVJ), 10-m and 20-m linear sprints, T-test change-of-direction speed (T-CODS), reactive strength index (RSI), and the Wingate anaerobic power test-were assessed pre- and post-a 6-week training intervention (i.e., 18 sessions). All RST groups showed significant post-intervention improvements in physical fitness (main effect of time, p = 0.001), with greater adaptations compared with the control group and effect sizes ranging from small to very large. The 3-sec bout group demonstrated greater gains in CMVJ, 10-m and 20-m sprint performance, RSI, and peak power output compared with the 9-sec group (all, p < 0.05). Conversely, the 9-sec group exhibited superior adaptations in T-CODS and mean power output relative to the 3-sec group (all, p < 0.05). In conclusion, the 3-sec group experienced greater enhancements in explosive and sprint performances, while the 9-sec group showed superior gains in change of direction and mean power output. These findings indicate that manipulation of sprint-bout duration in RST can be used to optimize distinct performance adaptations in young volleyball players.