The depletion or reduction of bodily carbohydrate reserves is associated with fatigue during endurance exercise. Various carbohydrate supplementation and exercise regimens have been used experimentally to increase carbohydrate reserves before exercise or to maintain the availability of carbohydrate for oxidation during exercise. On the other hand, the improved endurance capability observed after aerobic training has been attributed to an increased oxidation of fat relative to carbohydrate; this carbohydrate sparing presumably delays the point at which reduced carbohydrate reserves cause fatigue. This effect has led to the suggestion that a greater availability of fat during exercise can improve performance via the carbohydrate-sparing effect of “fat loading.” Although this is a plausible hypothesis, it is not supported by a sufficient number of valid, credible, and replicated studies. Thus, it appears prudent to advise endurance athletes to consume a diet that is largely carbohydrate to optimize training and competitive performance and, more importantly, to promote optimal health.
W. Michael Sherman and Nicole Leenders
Nicole Leenders, W. Michael Sherman, David R. Lamb and Timothy E. Nelson
The purpose of this study was to determine if oral creatine (CR) ingestion, compared to a placebo (PL), would enable swimmers to maintain a higher swimming velocity across repeated interval sets over 2 weeks of supplementation. Fourteen female and 18 male university swimmers consumed a PL during a 2-week baseline period. Using a randomized, double-blind design, during the next 2 weeks subjects consumed either CR or PL. Swimming velocity was assessed twice weekly during 6 × 50-m swims and once weekly during 10 × 25-yd swims. There was no effect ofCR on the 10 × 25-yd interval sets for men and women and no effect on the 6 × 50-m interval sets for women. In contrast, for men, CR significantly improved mean overall swimming velocity in the 6 × 50-m interval after 2 weeks of supplementation, whereas PL had no effect. Although ineffective in women, CR supplementation apparently enables men to maintain a faster mean overall swimming velocity during repeated swims each lasting about 30 s; however, CR was not effective for men in repeated swims each lasting about 10-15 s.