Time spent at or near VO₂max during high-intensity interval training - a systematic review and meta-analysis

BACKGROUND: max) has emerged as a key marker of the adaptive potential of HIIT, yet HIIT configurations that maximise tV̇O₂max remain unclear. OBJECTIVE: This systematic review and meta-analysis examined acute tV̇O₂max responses across various HIIT protocols, aiming to identify configurations with the greatest potential to stimulate training adaptations. METHODS: PubMed and Scopus were systematically searched to September 2025 for studies reporting tV̇O₂max during HIIT, defined as time spent at or above ≥ 80% V̇O₂max. Associations between protocol characteristics and tV̇O₂max were evaluated using ANCOVAs and linear mixed-effects models, while random-effects meta-analyses compared standardised mean differences (SMDs) across HIIT configurations, recovery modalities (active vs passive), and exercise intensity distributions in work intervals. RESULTS: max was determined for a total of 239 HIIT protocols. Protocols with long work intervals (≥ 2 min) elicited significantly greater tV̇O₂max than short (≤ 30 s) or moderate (> 30 s to < 2 min) work intervals, and linear mixed-effects models confirmed a positive relationship between cumulative HIIT duration and time ≥ 90% and ≥ 95% V̇O₂max when longer work intervals were used. Protocols incorporating variable-intensity work intervals further increased tV̇O₂max compared to even-paced formats (SMD = 0.80, p < .01). In contrast, recovery modality (active vs passive) showed no effect on tV̇O₂max. CONCLUSIONS: tV̇O₂max exhibits considerable variability, and its dose-response relationship with long-term adaptations requires further investigation. Nevertheless, HIIT protocols with longer and variable-intensity work intervals maximise tV̇O₂max, providing researchers, practitioners, and athletes with a firmer foundation for understanding how specific protocols shape the physiological demands and adaptive potential of a workout.