Effect of timing of carbohydrate ingestion on endurance exercise performance
McConell, G.; Kloot, K.; Hargreaves, M.
Medicine and Science in Sports and Exercise 28(10): 1300-1304
1996
ISSN/ISBN: 0195-9131 PMID: 8897388 Document Number: 459708
This study compared the effects of carbohydrate ingestion throughout exercise with ingestion of an equal amount of carbohydrate late in exercise. Eight well-trained men cycled 2 h at 70 +- 1% ovrhdot VO-2 peak, followed immediately by a 15-min performance ride, while ingesting either a 7% carbohydrate-electrolyte solution (CHO-7), an artificially sweetened placebo (CON), or the placebo for the first 90 min then a 21% glucose solution (CHO-0/21). At the start of the performance ride, plasma glucose averaged 4.2 +- 0.2, 5.2 +- 0.1, and 5.7 +- 0.2 mmol cntdot l-1 in CON, CHO-7, and CHO-0/21, respectively (all different, P lt 0.05). Plasma insulin levels were similar just prior to the performance ride in CHO-7 and CHO-0/21, with both higher than CON. A similar pattern was observed with respiratory exchange ratio (RER). Work performed during the performance ride was significantly greater in CHO-7 (268 +- 8 kJ) compared with CON (242 +- 9 kJ). Performance in CHO-0/21 (253 +- 10 kJ), however, was not improved compared with CON, despite higher plasma glucose levels and plasma insulin levels similar to CHO-7. Seven of the eight subjects performed best in CHO-7. In conclusion, performance was improved, relative to the control trial, only when carbohydrate was ingested throughout exercise. Carbohydrate ingestion late in exercise did not improve performance despite increases in plasma glucose and insulin. Sport scientists have identified many factors as prerequisites for a good athletic performance in various sports. It is not clear whether these factors also influence the best performers in the homogeneous groups of top athletes selected for national teams. In this study, this issue is addressed with members of the Dutch National Junior Speed Skating Team. A total of 237 different technical, physiological, anthropometrical, and psychological parameters were collected, including many that correlated with performance in previous studies. High speed film analyses during the National Championships provided the technique parameters. A 30-s sprint test and a 150-s supramaximal test on a cycle ergometer underlie the physiological data, and questionnaires were used to measure personality traits and emotional feelings. Only trunk position and the direction of push-off (push-off angle (p) correlated consistently with skating performance in this group (r = 0.61-0.73 and r = -0.65 to -0.70, respectively). The small number of meaningful correlations means that sport scientists will have to develop more reliable methods, models, and theories to contribute significantly to knowledge useful to top athletes and their coaches.