Coingestion of protein and carbohydrate in the early recovery phase, compared with carbohydrate only, improves endurance performance despite similar glycogen degradation and AMPK phosphorylation.

The present study compared the effects of postexercise carbohydrate plus protein (CHO+PROT) and carbohydrate (CHO)-only supplementation on muscle glycogen metabolism, anabolic cell signaling, and subsequent exercise performance. Nine endurance-trained males cycled twice to exhaustion (muscle glycogen decreased from ~495 to ~125 mmol/kg dry wt) and received either CHO only (1.2 g·kg-1·h-1) or CHO+PROT (0.8/0.4 g·kg-1·h-1) during the first 90 min of recovery. Glycogen content was similar before the performance test after 5 h of recovery. Glycogen synthase (GS) fractional activity increased after exhaustive exercise and remained activated 5 h after, despite substantial glycogen synthesis (176.1 ± 19.1 and 204.6 ± 27.0 mmol/kg dry wt in CHO and CHO+PROT, respectively; P = 0.15). Phosphorylation of GS at site 3 and site 2+2a remained low during recovery. After the 5-h recovery, cycling time to exhaustion was improved by CHO+PROT supplementation compared with CHO supplementation (54.6 ± 11.0 vs. 46.1 ± 9.8 min; P = 0.009). After the performance test, muscle glycogen was equally reduced in CHO+PROT and CHO. Akt Ser473 and p70s6k Thr389 phosphorylation was elevated after 5 h of recovery. There were no differences in Akt Ser473, p70s6k Thr389, or TSC2 Thr1462 phosphorylation between treatments. Nitrogen balance was positive in CHO+PROT (19.6 ± 7.6 mg nitrogen/kg; P = 0.04) and higher than CHO (-10.7 ± 6.3 mg nitrogen/kg; P = 0.009). CHO+PROT supplementation during exercise recovery improved subsequent endurance performance relative to consuming CHO only. This improved performance after CHO+PROT supplementation could not be accounted for by differences in glycogen metabolism or anabolic cell signaling, but may have been related to differences in nitrogen balance.NEW & NOTEWORTHY Endurance athletes competing consecutive days need optimal dietary intake during the recovery period. We report that coingestion of protein and carbohydrate soon after exhaustive exercise, compared with carbohydrate only, resulted in better performance the following day. The better performance after coingestion of protein and carbohydrate was not associated with a higher rate of glycogen synthesis or activation of anabolic signaling compared with carbohydrate only. Importantly, nitrogen balance was positive after coingestion of protein and carbohydrate, which was not the case after intake of carbohydrate only, suggesting that protein synthesis contributes to the better performance the following day.

AMPKα is essential for acute exercise-induced gene responses but not for exercise training-induced adaptations in mouse skeletal muscle.

Exercise training increases skeletal muscle expression of metabolic proteins improving the oxidative capacity. Adaptations in skeletal muscle by pharmacologically induced activation of 5'-AMP-activated protein kinase (AMPK) are dependent on the AMPKα2 subunit. We hypothesized that exercise training-induced increases in exercise capacity and expression of metabolic proteins, as well as acute exercise-induced gene regulation, would be compromised in muscle-specific AMPKα1 and -α2 double-knockout (mdKO) mice. An acute bout of exercise increased skeletal muscle mRNA content of cytochrome c oxidase subunit I, glucose transporter 4, and VEGF in an AMPK-dependent manner, whereas cluster of differentiation 36 and fatty acid transport protein 1 mRNA content increased similarly in AMPKα wild-type (WT) and mdKO mice. During 4 wk of voluntary running wheel exercise training, the AMPKα mdKO mice ran less than WT. Maximal running speed was lower in AMPKα mdKO than in WT mice but increased similarly in both genotypes with exercise training. Exercise training increased quadriceps protein content of ubiquinol-cytochrome c reductase core protein 1 (UQCRC1), cytochrome c, hexokinase II, plasma membrane fatty acid-binding protein, and citrate synthase activity more in AMPKα WT than in mdKO muscle. However, analysis of a subgroup of mice matched for running distance revealed that only UQCRC1 protein content increased more in WT than in mdKO mice with exercise training. Thus, AMPKα1 and -α2 subunits are important for acute exercise-induced mRNA responses of some genes and may be involved in regulating basal metabolic protein expression but seem to be less important in exercise training-induced adaptations in metabolic proteins.