CHO NEEDS TO BE INGESTED IF IT IS TO BE USED DURING EXERCISE
Wee, S. L., Williams, C., & Garcia-Roves, P. (1999). Carbohydrate availability determines endurance running capacity in fasted subjects. Medicine and Science in Sports and Exercise, 31(5), Supplement abstract 299.
This study evaluated the effects of different amounts of preexercise carbohydrate and fat on metabolism and endurance running capacity. Fasted endurance runners (N = 6) ran to exhaustion on a level treadmill at a work intensity of 71% VO2max. Three hours before testing, Ss consumed one of the following meals; high CHO-low fat (CM), low CHO-high fat (FM), or high CHO-high fat (HM).
Plasma glucagon concentrations were higher 60 minutes into exercise in the FM condition than in the other two. Plasma FFA and glycerol concentrations were highest during exercise in the FM condition. During the first 80 minutes of exercise in the FM trial, total CHO oxidation was 19% and 14% lower than during the CM and HM trials. All differences were statistically significant.
"We conclude that CHO, rather than fat availability, before exercise exerts predominant control over substrate selection during exercise and determines endurance running capacity."
Implication. Carbohydrate needs to be ingested before endurance exercise if it is to be available during exercise.
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