Time spent at or near V̇O₂max during high-intensity interval training - a systematic review and meta-analysis

Background High-intensity interval training (HIIT) is widely recognised as an effective strategy to improve cardiorespiratory fitness and endurance performance. Time spent at or near maximal oxygen uptake (tV̇O2max) 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 The literature search yielded 86 unique articles, in which tV̇O2max 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.