mTBI appeared to have little effect on cortical excitability, but an acute and long-lasting effect on intra-cortical inhibition.

Aim High-intensity interval training (HIT) results in potent metabolic adaptations in skeletal muscle, however little is known about the influence of these adaptations on energetics in vivo. We used magnetic resonance spectroscopy to examine the effects of HIT on ATP synthesis from net PCr breakdown (ATPCK), oxidative phosphorylation (ATPOX) and non-oxidative glycolysis (ATPGLY) in vivo in vastus lateralis during a 24-s maximal voluntary contraction (MVC). Methods Eight young men performed 6 sessions of repeated, 30-s “all-out” sprints on a cycle ergometer; measures of muscle energetics were obtained at baseline, and after the first and sixth sessions. Results Training increased peak 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 ergometer, with no effects on total ATP production or force-time integral during the MVC. While ATP production by each pathway was unchanged after the first session, 6 sessions increased the relative contribution of ATPOX (from 31±2 to 39±2% of total ATP turnover, p<0.001), and lowered the relative contribution from both ATPCK (49±2 to 44±1%, p=0.004) and ATPGLY (20±2 to 17±1%, p=0.03). Conclusion These alterations to muscle ATP production in vivo indicate that brief, maximal contractions are performed with increased support of oxidative ATP synthesis, and relatively less contribution from anaerobic ATP production following training. These results extend previous reports of molecular and cellular adaptations to HIT and show that 6 training sessions are sufficient to alter in vivo muscle energetics, which likely contributes to increased exercise capacity after short-term HIT.

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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

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