Abstract Introduction Exercise with low carbohydrate availability increases protein degradation, which may reduce subsequent performance considerably. The present study aimed to investigate the effect of carbohydrate ingestion during standardized exercise with and without exhaustion on protein degradation and next-day performance. Methods Seven trained male cyclists (VO2max 66.8 ± 1.9 mL·kg-1·min-1; mean ± SEM) cycled to exhaustion (~2.5 h) at a power output eliciting 68% of VO2max (W68%). This was followed by repeating 1-min work/1-min recovery intervals at 90% of VO2max (W90%) until exhaustion. During W68%, cyclists consumed a placebo water drink (PLA) the first time and a carbohydrate drink (CHO), 1 g carbohydrate·kg-1·h-1, the second time. The participants performed the same amount of work under the two conditions, separated by at least 1 wk. A standardized diet was provided to the participants so that the two conditions were isoenergetic. To test the impact of carbohydrates on recovery, participants completed a time trial (TT) the next day. Results Carbohydrate ingestion maintained carbohydrate availability during W68% and W90%: total carbohydrate oxidation was significantly higher in CHO (P = 0.022), and plasma glucose concentration was maintained compared with PLA (P = 0.025). Next-day performance during TT was better after CHO ingestion (CHO, 41:49 ± 1:38 min; PLA, 42:50 ± 1:46 min; P = 0.020; effect size d = 0.23, small), as was gross efficiency (CHO, 18.6% ± 0.3%; PLA, 17.9% ± 0.3%; P = 0.019). Urinary nitrogen excretion (P = 0.897) and urinary 3-methylhistidine excretion (P = 0.673) did not significantly differ during the study period. Finally, tyrosine and phenylalanine plasma concentrations increased in PLA but not in CHO (P = 0.018). Conclusions Carbohydrate ingestion during exhaustive exercise reduced deterioration in next-day performance through reduced metabolic stress and development of fatigue. In addition, some parameters point toward less protein degradation, which would preserve muscle function.
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