Short‐term, high‐intensity interval training (HIT) alters ATP pathway fluxes during maximal muscle contractions in humans

Abstract

Phosphorus magnetic resonance spectroscopy (MRS) was used to examine the effects of 2 weeks of cycling training on bioenergetics of vastus lateralis in vivo. Eight healthy, untrained men (27 ± 4 yr) performed 6 sessions of HIT (4–6 bouts of 30‐s all‐out cycling). At baseline, and after the 1st and the 6th training sessions, rates of ATP synthesis from net PCr breakdown (ATPCK), glycolysis (ATPGLY) and oxidative phosphorylation (ATPOX) were measured during a 24‐s maximal voluntary isometric contraction (MVIC) in a 4T magnet. Training increased peak whole‐body oxygen uptake (36 ± 4 to 39 ± 5ml·kg−1·min−1, p=0.01) and exercise capacity (225 ± 32 to 239 ± 36 W, p=0.04) on the cycle ergometer, with no effects on total ATP production or force‐time integral during the MVIC. While ATP production through the 3 pathways remained unchanged after the first training session, 6 training sessions increased the relative contribution of ATPOX (31 ± 2 vs. 39 ± 2% of total ATP turnover, p<0.001), and lowered the relative contribution from ATPCK (49 ± 2 vs. 44 ± 1%, p=0.004) and ATPGLY (20 ± 2 vs. 17 ± 1%, p=0.03). Thus, 6 sessions of HIT alters muscle energetics, such that maximal contractions are performed with increased support from oxidative ATP synthesis and relatively less contribution from anaerobic ATP production, which may contribute to improved exercise capacity.Support: NIH K02 AG023582