This study examined the effects of serial feedings of different carbohydrate (CHO) solutions on plasma volume, gastric emptying (GE), and performance during prolonged cycling exercise. Solutions containing 6 g% glucose-sucrose (CHO-6GS), 83 g% high fructose com syrup (CHO-8HF), 6.3 g% high fructose corn syrup + 2 g% glucose polymer (CHO-8HP), and a water placebo (WP) were compared. Ten trained male cyclists performed four cycling trials consisting of 105 min at 70% VQ2max followed by a 15-min all-out, self-paced performance ride. Every 15 min the men consumed one of the four test solutions. Blood samples were taken before, during, and after exercise to determine blood glucose and plasma volume changes. There were no significant differences in performance, GE, or plasma volume changes between trials. Blood glucose was significantly elevated at the 105-min timepoint in all CHO trials when compared to WP. The CHO-8HF and CHO-8HP drinks resulted in a significantly higher delivery of CHO to the intestine. Higher rates of CHO oxidation during the steady-state ride were observed only with the CHO-6GS drink.
Kevin J. Cole, Peter W. Grandjean, Richard J. Sobszak, and Joel B. Mitchell
Christopher Barnett, David L. Costill, Mathew D. Vukovich, Kevin J. Cole, Bret H. Goodpaster, Scott W. Trappe, and William J. Fink
This study examined the effects of 14 days of L-camitine supplementation on muscle and blood camitine fractions, and muscle and blood lactate concentrations, during high-intensity sprint cycling exercise. Eight subjects performed three experimental trials: control 1 (CON I, Day 0), control I! (CON II, Day 14), and L-camitine (L-CN, Day 28). Each trial consisted of a 4-rain ride at 90%
Kevin J. Cole, David L. Costill, Raymond D. Starling, Bret H. Goodpaster, Scott W. Trappe, and William J. Fink
The purpose of this investigation was to determine the effect of caffeine ingestion on work output at various levels of perceived exertion during 30 min of isokinetie variable-resistance cycling exercise. Ten subjects completed six trials 1 hr after consuming either 6 mg · kg−1 caffeine (3 trials) or a placebo (3 trials). During each trial the subjects cycled at what they perceived to be a rating of 9 on the Borg rating of perceived exertion scale for the first 10 min, a rating of 12 for the next 10 min, and a rating of 15 for the final 10 min. Total work performed during the caffeine trials averaged 277.8 ± 26.1 kJ, whereas the mean total work during the placebo trials was 246.7 ± 21.5 kJ (p < .05). Blood glycerol and free fatty acid levels increased over time to a significantly greater degree in the caffeine trials than in the placebo trials (p < .05). However, there were no significant differences between conditions in respiratory exchange ratio. These data suggest that caffeine may play an ergogenic role in exercise performance by altering both neural perception of effort and substrate availability.