Effect of carbohydrate ingestion and hormonal responses on ratings of perceived exertion during prolonged cycling and running

This randomized, double-blind, placebo-controlled study was designed to det ermine the influence of exercise mode, and 6% carbohydrate (C) versus place bo (P) beverage ingestion, on ratings of perceived exertion (RPE) and hormo nal regulation to 2.5 h of high-intensity running and cycling (approximate to 75% maximum oxygen uptake) by ten triathletes who acted as their own con trols. Statistical significance was set at P less than or equal to 0.05. Th e pattern of change in RPE over time was significantly different between C and P ingestion (P < 0.001) and between running and cycling modes (P = 0.00 1). The lowest RPE values were seen in the C-cycling sessions and the highe st in the P-running sessions, The pattern of change in the respiratory exch ange ratio and fat and carbohydrate oxidation rates were significantly diff erent between the C and P conditions but not between the running and cyclin g modes. C relative to P ingestion (but not exercise mode) was associated w ith higher plasma levels of glucose and insulin and lower plasma cortisol a nd growth hormone levels. The pattern of change in plasma levels of catecho lamines and lactate did not differ between the C and P conditions. These da ta indicate that a lower RPE was associated with a higher level of carbohyd rate oxidation, higher plasma glucose and insulin levels, and lower plasma cortisol and growth hormone levels during cycle exercise following C supple mentation as compared to P feeding. These findings support a physiological link between RPE and carbohydrate substrate availability as well as selecte d hormonal regulation during cycle exercise.