Poon et al. 2024, HIIT and cardiorespiratory fitness in adults: umbrella review

This umbrella review of 24 systematic reviews and meta-analyses covering hundreds of primary studies found that HIIT consistently and significantly increases cardiorespiratory fitness (VO₂max/VO₂peak) in adults compared with both non-exercise control conditions and moderate-intensity continuous training (MICT). The effect held across diverse adult populations. Strong evidence from the highest rung of the evidence hierarchy.