Effects of pre-exercise carbohydrate feedings on muscle glycogen use during exercise in well-trained runners.

The purpose of this study was to examine the effects of pre-exercise glucose and fructose feedings on muscle glycogen utilization during exercise in six well-trained runners (VO2max = 68.2 +/- 3.4 ml X kg-1 X min-1). On three separate occasions, the runners performed a 30 min treadmill run at 70% VO2max. Thirty minutes prior to exercise each runner ingested 75 g of glucose (trial G), 75 g of fructose (trial F) or 150 ml of a sweetened placebo (trial C). During exercise, no differences were observed between any of the trials for oxygen uptake, heart rate or perceived exertion. Serum glucose levels were elevated as a result of the glucose feeding (P less than 0.05) reaching peak levels at 30 min post-feeding (7.90 +/- 0.24 mmol X l-1). With the onset of exercise, glucose levels dropped to a low of 5.89 +/- 0.85 mmol X l-1 at 15 min of exercise in trial G. Serum glucose levels in trials F and C averaged 6.21 +/- 0.31 mmol X l-1 and 5.95 +/- 0.23 mmol X l-1 respectively, and were not significantly different (P less than 0.05). There were also no differences in serum glucose levels between any of the trials at 15 and 30 min of exercise.

RCT Entities:   Population Interventions Outcomes