Abstract
OBJECTIVE: To (i) examine the effect size and the ranking of the training effects for the high-intensity interval training (HIIT), sprint interval training (SIT), and repeated sprint training (RST) on athletes' VO(2)max through network meta-analysis. (ii) investigate the effects of the training program protocols of the three methods on the improvement of VO(2)max through pairwise meta-analysis and meta-regression. METHODS: A systematic search of four databases (Web of Science, PubMed, Scopus, SPORTDiscus) were conducted on April 1, 2025. 51 eligible studies (1,261 athletes), evaluating the direct/indirect effects of HIIT, SIT, RST versus continuous training (CT) and conventional training (CON). Frequentist network meta-analysis quantified effect sizes (NMAs' g) and probabilistic rankings (P-scores), while three-level meta-regression modeled dose-response relationships for training parameters. RESULTS: All three interval training methods significantly increased VO(2)max compared to CON, with NMA rankings: RST (NMA's g = 1.04) > HIIT (NMA's g = 1.01) > SIT (NMA's g = 0.69) > CT (NMA's g = 0.29), no significant differences existed among RST, HIIT, and SIT (p > 0.05). Subgroup analyses showed HIIT efficacy was moderated by athlete level, whereas SIT improvements were influenced by intervention duration, training frequency, and training mode. Meta-regression identified inverted U-shaped relationships for HIIT, with peak benefits at 140 s work duration and a work-to-recovery ratio (WRR) of 0.85. For SIT, improvements are not significant when recovery durations exceeding 97 s. CONCLUSIONS: RST, HIIT, and SIT all enhance VO(2)max in athletes, with RST demonstrating the strongest probabilistic efficacy. Optimal protocols include 3-6 weeks of running-based HIIT (140 s work, 165 s recovery) or SIT (≤ 30 s sprints, < 97 s recovery) at 3 sessions per week. Conducting RST 3 sessions a week for two weeks is sufficient to achieve improvements. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42023435021.