Effects of high-intensity interval training on cardiorespiratory fitness in adolescents with overweight or obesity: a systematic review and dose-response meta-analysis.

BACKGROUND: Adolescents with overweight or obesity commonly exhibit reduced cardiorespiratory fitness (CRF), which is closely associated with cardiometabolic risk and premature mortality in adulthood. High-intensity interval training (HIIT) has been proposed as a time-efficient exercise strategy; however, quantitative evidence regarding the dose of HIIT in adolescents with overweight or obesity remains limited. Objective: This study aimed to evaluate the effects of HIIT on CRF in adolescents with overweight or obesity and to explore the nonlinear association between weekly HIIT dose and improvements in CRF using dose-response meta-analysis. METHODS: PubMed, Embase, Web of Science, Scopus, and CNKI were searched from database inception to March 2026. Eligible studies were randomized controlled trials involving adolescents aged 10-18 years with overweight or obesity. Interventions consisted of structured HIIT or sprint interval training, and comparators included usual care, health education, or no additional structured exercise. The outcomes were VO2max/VO2peak measured in the laboratory, or equivalent CRF indices estimated using standardized field tests. Two reviewers independently performed study screening, data extraction, and risk-of-bias assessment using the RoB 2 tool. Random-effects meta-analysis was used to Hedges' g, and restricted cubic splines were further applied to examine the nonlinear relationship between weekly HIIT dose (MET-min/week) and CRF improvement. RESULTS: Sixteen randomized controlled trials, including 19 effect sizes were included. Compared with control conditions, HIIT significantly improved CRF (Hedges' g, 1.13, 95% CrI: 0.80-1.50). Exploratory subgroup analyses suggested more stable positive effects in studies using three sessions per week, a work-to-recovery ratio of approximately 1:1, and VO2max/VO2peak as the CRF outcome. Exploratory dose-response analysis suggested an inverted U-shaped association between weekly HIIT dose and CRF improvement, with the largest predicted effect observed at approximately 360 MET-min/week. However, this estimate should be interpreted cautiously because of the limited number of trials, between-study heterogeneity, and assumptions involved in MET-min/week conversion. CONCLUSIONS: HIIT may be an effective strategy for improving CRF in adolescents with overweight or obesity. Its benefits appear to depend not only on the use of HIIT per se, but also on training frequency, work-recovery structure, and weekly dose. Current evidence suggests a possible nonlinear association between weekly HIIT dose and CRF improvement; however, this finding is hypothesis-generating rather than definitive and should be verified in larger trials with standardized HIIT prescription reporting, transparent dose coding, and longer follow-up. SYSTEMATIC REVIEW REGISTRATIONS: https://www.crd.york.ac.uk/PROSPERO, identifier CRD420261392042.