Guth, L. M., Craft, K. A., & Mahon, A. D. (2010). Effects of carbohydrate supplementation on variable-intensity exercise responses in boys and men. Presentation 856 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

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This study examined the effects of carbohydrate supplementation in children and men during activity of an intermittent and variable nature, somewhat akin to that which occurs in free-play and sport. Boys (N = 5, age = ~11.3 years) and men (N = 7, age = ~23.8 years) of similar aerobic fitness consumed 1.5g/kg of carbohydrate (CHO) or a placebo (beverage before and throughout a variable-intensity exercise protocol. The exercise protocol included three 12-minute sets of cycling with intensity varying every 20-30 seconds between 25 and 125% VO2peak. Blood glucose and lactate concentrations were measured before and every 12 minutes during exercise. VO2 and respiratory exchange ratio were measured during the second 12-minute set of variable exercise and perceived exertion was recorded every six minutes.

VO2 expressed as a percentage of VO2peak was similar between boys and men during variable-intensity exercise and was not affected by CHO. In the CHO condition, men had higher pre-exercise blood glucose concentrations than boys. In the placebo condition, men had higher post-exercise blood glucose than boys. In boys, post-exercise blood glucose was lower during the placebo trial compared to the CHO trial. Respiratory exchange ratio was significantly lower in boys than men and increased over time, but was not significantly affected by CHO supplementation. Men had significantly higher lactate than boys throughout the exercise. In men, lactate was significantly elevated at all exercise time points, while in boys lactate was only significantly increased after the first 12-minute set. Rating of perceived exertion increased over time during, but did not differ between boys and men and was not affected by CHO supplementation.

Implication. Some physiological responses to variable-intensity exercise varied between boys and men. However, CHO supplementation prior to and during exercise does not provide a physiological or perceptual benefit to either boys or men. Physiological and biochemical changes were noted, but no performance gains demonstrated. This study was further refutation of the belief that if physiology changes, so does performance.

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