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 post exercise carbohydrate plus protein (CHO+PROT) and carbohydrate (CHO) only supplementation on muscle glycogen metabolism, anabolic cell signalling and subsequent exercise performance. Nine endurance-trained males cycled twice to exhaustion (muscle glycogen decreased from ~495 to ~125 mmol·kg dw^-1) 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 dw^-1 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 to 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 PRO+CHO 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^-1, p=0.04) and higher than CHO (-10.7±6.3 mg nitrogen·kg^-1, p=0.009). 

Conclusion: 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.