A Low Carbohydrate, Moderate Protein Beverage Improves Submaximal Endurance Cycling Performance In Trained Cyclists

Abstract

PURPOSE: Supplementing with carbohydrate plus protein during prolonged variable intensity exercise has been found to improve aerobic endurance performance beyond that of a carbohydrate supplement alone, although this is currently controversial. The controversy may arise due to the varying ability of individuals to sustain exercise at different percentages of VO2max. The purpose of the present study was to compare the effects of a carbohydrate only supplement and a lower carbohydrate plus moderate protein supplement on cycling endurance performance at or above ventilatory threshold (VT). METHODS: Fifteen trained male and female cyclists (8 males, 7 females) exercised on two separate occasions at intensities that varied between 45% and 70% VO2max for 3 h, and then at 80% VO2max until exhaustion. The supplements (275 ml) were provided every 20 min during exercise and consisted of a 6% carbohydrate solution (CHO) and a 3% carbohydrate/1.2% protein solution (CP). Treatments were administered using a double-blind randomized design. RESULTS: At 80% of VO2max, no significant differences were found between treatments. However, significant treatment differences were found when subjects were grouped according to the % of VT at which they cycled. No difference in treatment response was noted when subjects (N= 7) cycled at work rates greater than 7% of VT (CHO, 15.2 min ± 2.8 SEM; CP, 14.4 min ± 2.5 SEM). However, subjects that cycled at a work rate within 2% of VT had improved endurance performance with CP (44.9 min ± 6.8 SEM) vs CHO (37.2 min ± 7.4 SEM, p= <.05). CONCLUSIONS: The results suggest that the addition of protein to a CHO supplement can improve aerobic endurance at exercise intensities around the VT and that this improvement can occur even if the CP supplement is lower in total caloric content in comparison to the CHO supplement. These results also suggest that the addition of protein may not be beneficial when the work rate is substantially above the ventilatory threshold and may account for the contradictory findings in the literature regarding the benefit of a carbohydrate-protein supplement.