Impact of protein coingestion on muscle protein synthesis during continuous endurance type exercise.

This study investigates the impact of protein co-ingestion with carbohydrate on muscle protein synthesis during endurance type exercise. Twelve healthy male cyclists were studied during 2 h of fasted rest, followed by 2 h of continuous cycling at 55% W(max). During exercise, subjects received either 1.0 g*kg(-1)*h(-1) carbohydrate (CHO) or 0.8 g*kg(-1)*h(-1) carbohydrate with 0.2 g*kg(-1)*h(-1) protein hydrolysate (CHO+PRO). Continuous intravenous infusions with L-[ring-(13)C(6)] phenylalanine and L-[ring-(2)H(2)] tyrosine were applied, and blood and muscle biopsies were collected to assess whole-body protein turnover and muscle protein synthesis rates at rest and during exercise conditions. Protein co-ingestion stimulated whole-body protein synthesis and oxidation rates during exercise by 22+/-3% and 70+/-17%, respectively (P<0.01). Whole-body protein breakdown rates did not differ between experiments. As a consequence, whole-body net protein balance was slightly negative in CHO and positive in the CHO+PRO treatment (-4.9+/-0.3 vs 8.0+/-0.3 mumol phe*kg(-1)*h(-1), respectively; P<0.01). Mixed muscle protein fractional synthetic rates (FSR) were higher during exercise when compared with resting conditions (0.058+/-0.006 vs 0.035+/-0.006%*h(-1) in CHO and 0.070+/-0.011 vs 0.038+/-0.005%*h(-1) in the CHO+PRO treatment, respectively; P<0.05). FSR during exercise did not differ between experiments (P=0.29). We conclude that muscle protein synthesis is stimulated during continuous endurance type exercise activities when ingesting carbohydrate with or without protein. Protein co-ingestion does not further increase muscle protein synthesis rates during continuous endurance type exercise.