EFFECT OF CARBOHYDRATE SUBSTRATE AVAILABILITY ON RATINGS OF PERCEIVED EXERTION DURING PROLONGED RUNNING 111

To investigate the effect of carbohydrate substrate availability on ratings of perceived exertion (RPE) during prolonged submaximal running, thirty marathon runners were recruited as subjects to participate the study. These subjects were randomly assigned to either carbohydrate or placebo feeding group. Each subject performed an experimental trial consisted of a 2.5-h treadmill running at 75-80% VO2max. During the trial, the subjects of carbohydrate feeding group ingested a 6% glucose solution at the rate of approximately 60 g·h-1, whereas the subjects of placebo feeding group consumed an equal volume of artifically flavored placebo every 15 min. RPE, oxygen uptake (VO2), respiratory exchange ratio (RER) and expiratory ventilation (VE) were measured every 20 min throughout the exercise and at the exercise termination. Carbohydrate oxidation rate was estimated from VO2 adjusted for RER. Blood glucose concentration was also determined prior to and immediately after the exercise. RPE did not differ between the groups during the first 60 min but was lower (p<0.05) in carbohydrate than placebo group beginning at 60 min and thereafter. RER was higher (P<0.05) in carbohydrate than placebo group beginning at 80 min and thereafter. VE did not differ throughout the exercise between the two groups. Carbohydrate oxidation rate was higher (p<0.05) in carbohydrate than placebo group at 140 and 150 min of exercise. Blood glucose concentration immediately after exercise was also higher (p<0.05) in carbohydrate than placebo group. It is concluded that the increased carbohydrate oxidation attenuates intensity of exertional perceptions during the later stages of prolonged running at 75-80% VO2max in marathon runners. The finding of this investigation can be added to the current data to support the physiological link between carbohydrate substrate availability and strength of exertional perceptions.