A comparison of skeletal muscle oxygenation and fuel use in sustained continuous and intermittent exercise

In this study we compared substrate oxidation and muscle oxygen availability during sustained intermittent intense and continuous submaximal exercise with similar overall (i.e. work and recovery) oxygen consumption (V˙O₂). Physically active subjects (n?=?7) completed 90?min of an intermittent intense (12?s work:18?s recovery) and a continuous submaximal treadmill running protocol on separate days. In another experiment (n?=?5) we compared oxygen availability in the vastus lateralis muscle between these two exercise protocols using near-infrared spectroscopy. Initially, overall V˙O₂ (i.e. work and recovery) was matched, and from 37.5?min to 67.5?min of exercise was similar, although slightly higher during continuous exercise (8%; P??1?·?kg^?1] and continuous submaximal 0.85 (0.01)?kJ?·?min^?1?·?kg^?1] exercise. Overall exercise intensity, represented as a proportion of peak aerobic power (V˙O_2peak), was 68.1 (2.5)% V˙O_2peak and 71.8 (1.8)% V˙O_2peak for intermittent and continuous exercise protocols, respectively. Fat oxidation was almost 3 times lower (P?P?P?P?P?r?=?0.72; P?V˙O₂ and identical energy expenditure.