Effects and Moderators of High-Intensity Interval Training (HIIT) on Physiological Adaptations Among Team-Sport Athletes: A Systematic Review and Meta-Analysis

High-intensity interval training (HIIT) is widely used in team sports, but the influence of participant and programme characteristics on physiological adaptations remains unclear. Five databases (Web of Science Core Collection, PubMed, Embase, Scopus, and CNKI) were searched initially on 25 April 2025 and updated on 21 December 2025. Mixed-effects models were used to estimate Hedges' g and 95% confidence intervals (CI). Forty-six studies involving 1204 athletes were included. Compared with regular sport-specific training alone, HIIT produced positive effects on maximal oxygen uptake (VO₂max; g = 0.76, 95% CI [0.61, 0.92]), maximal aerobic power (g = 0.43, 95% CI [0.04, 0.82]), ventilatory threshold (g = 0.70, 95% CI [0.53, 0.88]), Yo-Yo intermittent recovery test performance (g = 1.02, 95% CI [0.76, 1.28]), and 30-s Wingate peak (g = 0.91, 95% CI [0.67, 1.16]) and mean power (g = 0.70, 95% CI [0.39, 1.01]). Effects on body composition were generally unclear. Mutually adjusted multivariable meta-regression identified no convincing evidence of differences in VO₂max or Yo-Yo intermittent recovery test performance effects by sex or training level. Longer training duration was associated with greater VO₂max effects. In exploratory analyses, model predictions indicated increases in VO₂max of 2.56 mL·kg^-1·min^-1 (95% CI [1.54, 3.58]) after approximately 5 weeks and 5.11 mL·kg^-1·min^-1 (95% CI [3.32, 6.91]) after approximately 10 weeks. Shorter between-repetition recovery was associated with greater VO₂max effects, although other programme variables were estimated imprecisely. Overall, adding HIIT to regular sport-specific training improves aerobic and anaerobic performance in trained team-sport athletes, whereas effects on body composition are limited. Associations involving programme characteristics should be interpreted cautiously because they were derived from study-level meta-regression. Trial Registration: PROSPERO Registration CRD42024609379.