Effects of high-intensity interval training on muscle oxidative metabolism in young men

The ability to supply cellular energy in the form of adenosine triphosphate (ATP) by oxidative phosphorylation is critical to maintaining muscle function and health. While conventional endurance exercise training has proven effective at increasing the maximal capacity for oxidative phosphorylation (Vmax ), it is not known whether exercise training stimulates mitochondrial ATP synthesis in resting muscle (Vrest). Recently, short-term high-intensity interval training (HIT) training has shown potent effects on Vmax. However, little is known about (1) the effects of short-term HIT on Vrest, and (2) the time course of adaptations in V rest and Vmax following short-term HIT. Healthy young males were recruited to participate in a 2-week training intervention (6 training sessions). Each session consisted of 4–6 bouts of 30-s sprints on a cycle ergometer. Phosphorus magnetic resonance spectroscopy was used to measure Vrest and Vmax in vivo in vastus lateralis: (i) prior to, (ii) 15 hours after a single session of exercise training, and (iii) after completing 6 sessions of exercise training. Two weeks of training increased peak whole-body oxygen consumption (35.8 ± 1.4 to 39.3 ± 1.6 ml·min−1·kg−1, p=0.01) and exercise capacity (217.0 ± 11.0 to 230.5 ± 11.7 W, p=0.04) on the cycle ergometer. While Vmax was unchanged after a single session of HIT, completion of six training sessions resulted in increased muscle oxidative capacity (p\u3c0.004). In contrast, neither a single nor six training sessions altered Vrest (p=0.74). Metabolic flux through each pathway, during maximal voluntary contractions, remained unchanged after the first training session, but 6 training sessions increased the relative contribution of ATPOX (31 ± 2 vs. 39 ± 2 % of total ATP turnover, p\u3c0.001), and lowered the relative contribution from ATP CK (49 ± 2 vs. 44 ± 1 %, p=0.004) and ATPGLY (20 ± 2 vs. 17 ± 1 %, p=0.03). This study provided novel information about the scope and timing of bioenergetic adaptations of skeletal muscle in young healthy men following high-intensity interval training. These results highlight the plasticity of skeletal muscle oxidative metabolism, which is critical for the design of future exercise training interventions for both clinical and healthy populations