Timing Of Glucose Supplementation To Optimize Performance In Repeated Bouts Of High Intensity Cycling

Abstract

Athletes participating in short duration sprint events must carefully choose their fuel strategy to maximize performance. PURPOSE: To determine whether glucose feeding taken immediately before, early, or late in a series of high-intensity cycling exercises affected cycling performance. METHODS: 16 trained, male cyclists (> 6hr post-prandial) participated in the study and performed three, 4-km cycling time trials (T1, T2, T3) separated by 15 min of active recovery on four separate occasions. Subjects completed a familiarization visit followed by randomized visits comprised of a control visit (CNT), and three visits in which glucose feeding (40g) was given either before the first time trial (PRE1), before the second time trial (PRE2), or before the third time trial (PRE3). Sweet-placebo was given prior to the other time trials. Data were collected on a Velotron cycle ergometer. Blood glucose (BG) was measured upon arrival and before and after each trial by capillary sampling. RESULTS: Peak power output (PPO) in PRE1, PRE2 and CNT were significantly lower (-4.5%, -4.5%, and -2.5%, respectively) in T2 than T1 (p < 0.05). PPO in PRE2 and PRE3 were significantly lower (-6.3% and -4.5%, respectively) in T3 than T1 (p < 0.05). BG in PRE1 was significantly higher (+23.3%) before T1 than PRE3 (p < 0.05). In T2, BG was significantly higher (+19.4%) in PRE2 than PRE3 prior to T2 (p < 0.05). BG in PRE2 was significantly higher (+14.2%) prior to T2 than T1 (p < 0.05). BG in PRE2 and PRE3 continued to increase 20.8% and 29%, respectively before trial 3. BG in PRE2 was significantly higher (43.4%) than the control prior to T3 (p < 0.05). BG in PRE2 and PRE3 were significantly higher (37.8 and 26.8%, respectively) in T3 than T1 (p < 0.05). BG in PRE2 and PRE3 were significantly higher (20.7 and 29%, respectively) in trial 3 than trial 2 (p < 0.05). CONCLUSION: There was a reduction in performance in repeated high-intensity exercise bouts with glucose feeding after the initial exercise bout, but no significant decrease in performance with pre-exercise feeding or fasting. Therefore, in order to optimize performance, athletes undertaking repeated high-intensity exercise bouts should ingest glucose prior to exercise, but not between exercise bouts.