Maintenance of hyperglycaemia does not improve perfomence in a 100 km cycling time trial

Abstract

Objectives. The aim of this study was to determine whether the elevated plasma glucose oxidation rate (~ 1.8 g.min-1) in the latter stages of prolonged exercise in subjects in which hyperglycaemia (± 10 mmol.l-1) is maintained via a glucose clamp, improves 100 km cycling time-trial (TT) performance. Design. Seven endurance-trained male cyclists (22±4 yrs) participated in this randomised crossover trial. On two occasions, separated by 7 - 10 days, subjects performed a self-paced TT in the laboratory. During one TT blood glucose was maintained at a euglycaemic concentration of ± 5 mmol.l-1 (ETT) and during the other, at ±10 mmol.l-1 (HTT). Each TT was interspersed with 5 X 1 km high-intensity periods (HIP) and 4 X 4 km HIP, in an attempt to mimic the variable intensity of competitive road races. Subjects were instructed to complete the TT in the ‘fastest time possible', taking the 9 HIP (21 km) into consideration. Results. There were no significant differences between ETT and HTT in overall time (143:09±7:14 v. 142:23±7:16 min:s), mean power (275±39 v. 279±39 W) and heart rate (160±9 v. 158±11 beats.min-1). Conclusion. Time trial performance over 100 km is not improved by maintaining a hyperglycaemic (10 mmol.l-1) blood glucose concentration.

South African Journal of Sports Medicine Vol. 19 (3) 2007: pp. 94-98