Ingesting a carbohydrate (CHO) solution during prolonged submaximal exercise appears to delay the onset of fatigue and enhance endurance performance, especially in exercise lasting more than 2 hours. However, whether CHO feeding affects cycling economy and efficiency during extended-duration exercise remains to be elucidated.
PURPOSE: The purpose of this study was to determine the effects of CHO ingestion (10%CHO solution: 60 g·h−1) on cycling economy and gross efficiency during 8 h of prolonged exercise.
METHODS: Seven moderately trained individuals [cycling %VO2peak at ventilatory threshold (Tvent); 63.8±7.1] served as subjects. All subjects randomly completed a placebo-controlled, double-blind, cross over-design. Each subject performed a total of 8 h of exercise including 25 min of leg cycling (freely chosen crank rate; average from 72 to 85 rpm) and 25 min of treadmill walking with 5 min of transition between modes each hour and a 30 min lunch rest period. Each exercise session consisted of a variety of intensities (min 0–6=70%Tvent, min 7–8=110%Tvent, min 9=70%Tvent, min 10–11=100%Tvent, min 12=70%Tvent, min 13–14=90%Tvent, min 15–25=70%Tvent). Cycling economy (w·l−1min−1) and gross efficiency (%) were determined during 70% Tvent from min 18 to 25 during hours 1,4, 5, and 8.
RESULTS: With a two-way repeated measures ANOVA, the main effect for trial for economy and gross efficiency and interaction (trial x time) were not statistically significant. However, the main effect for time demonstrated significant decreases at hour 8 compared to hour 4 in both economy (p < 0.01) and gross efficiency (p < 0.05).
CONCLUSION: Carbohydrate ingestion during 8 h of endurance exercise appears to have no influence on cycling economy and gross efficiency at relatively moderate intensity with freely chosen crank rate.