The effects of low-volume high-intensity interval training and circuit training on maximal oxygen uptake

High-intensity interval training (HIIT) and circuit training (CT) are popular methods of exercise, eliciting improvements in cardiorespiratory fitness (CRF). However, direct comparisons of these two training methods are limited. We investigated the effects of HIIT and CT on CRF. Thirty-nine apparently healthy middle-aged participants [HIIT; mean age: 42.5 ± 12.3; V̇O₂ₘₐₓ 31.5 ± 7.1 (ml kg−1 min−1); 52% males; CT; mean age: 41.2 ± 12.9; V̇O₂ₘₐₓ 31.4 ± 6.8 (ml kg−1 min−1); 57% males] were randomly allocated to two sessions per week of HIIT or CT over 8 weeks. HIIT performed ten 1-min cycle-ergometry intervals at > 85% HRmax, separated by ten 1-min intervals of active recovery. The CT group performed up to 40-min of CT at 60–80% HRmax. CRF was measured using maximum oxygen uptake ( V̇O₂ₘₐₓ ), ventilatory anaerobic threshold ( V̇O₂ at VAT) and maximum oxygen pulse ( V̇O₂ /HR). V̇O₂ₘₐₓ increased by 12% following HIIT (mean difference 3.9 ml kg−1 min−1; 95% CI: 2.8–4.9; P < 0.001), and 3% in CT (mean difference 1.0 ml kg−1 min−1; 95% CI: − 0.4 to 2.0; P = 0.060). V̇O₂ at VAT increased by 16% following HIIT (mean difference 2.4 ml kg−1 min−1; 95% CI: 1.6–3.1; P < 0.001) and 4% in CT (mean difference 0.7 ml kg−1 min−1; 95% CI: − 0.1 to 1.4; P = 0.085). V̇O₂ /HR increased by 11% following HIIT (mean difference 1.4 ml beat−1; 95% CI: 0.9–2.0; P < 0.001) and 1% after CT (mean difference 0.3 ml beat−1; 95% CI: − 0.3 to 0.8; P = 0.318). Our study demonstrated that HIIT led to greater improvements in CRF when compared to CT. ClinicalTrials.gov Identifier: NCT03700671.