Post-Exercise Feeding of Carbohydrate-Protein Beverages on Subsequent Endurance Performance

Abstract

Fatigue during prolonged exercise is associated with a reduction in muscle glycogen. Evidence suggest that a carbohydrate-protein beverage (CHO+PRO) is more effective for rapid restoration of muscle glycogen than carbohydrate alone (Ivy et al., 2002), but few have examined the effect of the composition of post-exercise feeding on subsequent endurance performance. PURPOSE: To compare cycling performance (time to fatigue; TTF) following ingestion of a beverage containing CHO+PRO, carbohydrate-only (CHO) or placebo (CON) over a 4 h period of rest recovery (REC) from prolonged cycling. METHODS: Six endurance trained athletes (5 males, 1 female: age 30.2 ± 3.7 y, height 175.7 ± 6.2 cm, body mass 70.0 ± 7.5 kg, VO2max 4.4 ± 0.6 L.min-1, mean ± SD) participated in three trial days, each trial day separated by at least seven days. Trial days comprised 120 min steady-state cycling (PRE: 6342 ± 279 kJ; carbohydrate oxidation 210 ± 12.2 g), a 4 h period of REC, followed by a steady-state cycle (POST) to volitional fatigue. All cycle trials were performed at ∼70% VO2max. During REC subjects consumed one of three beverages (2 L in volume), 1 L immediately after PRE and 500 mL at 1 h and 2 h of REC. Subjects ingested either flavoured water (CON), a solution containing 1 g CHO.kg-1.h-1 (CHO) or a solution containing 1 g CHO.kg-1.h-1 and 0.33 g protein.kg-1.h-1 (CHO+PRO). Beverages were administered double-blind. Energy expenditure and substrate metabolism during cycling were measured by the Douglas bag technique. RESULTS: Values are expressed mean ± SEM. No difference in energy expenditure or carbohydrate oxidation of PRE were observed. Compared to CON, mean time to fatigue (TTF) in the POST trial was 40% longer for CHO (55.2 ± 7.5 vs. 77.5 ± 16.1 min; p=0.668) and 68% longer for CHO+PRO (55.2 ± 7.5 vs. 92.8 ±9.0 mm: p=0.036). Compared to CON, average rate of carbohydrate oxidation was greater for CHO (1.3 ± 0.2 vs. 1.8 ± 0.3 g.min-1; p=0.184) and CHO+PRO (1.3 ± 0.2 vs. 2.5 ± 0.2 g.min-1;p=0.024). CONCLUSION: Ingestion of a CHO+PRO beverage during 4 h recovery from prolonged exercise resulted in a significantly higher rate of carbohydrate oxidation and post-recovery endurance performance. These data support previous reports of an ergogenic effect attributed to the rapid restoration of muscle glycogen when protein is added to a carbohydrate beverage.