The main purpose of this study was to investigate the influence of pre-exercise glucose ingestion after a 2.5-h fast on the endurance capacity and blood glucose response in East Asian athletes who is expected to have genetically low insulin response. A total of 8 Japanese student athletes ingested 1.5 g/kg body mass of glucose (G trial) or 0.5 g/kg body mass of artificial sweetener dissolved in water (P trial) 30 min before exercise test after consuming a standardized breakfast. The exercise test comprised 40 min cycling exercise at 50% maximal oxygen uptake (VO2max), immediately followed by cycling to exhaustion at 70% VO2max. Before analyzing the data, we grouped the subjects into two groups depending on whether they showed rapid increase in blood glucose at the onset of exercise (increase rate in LOW group is <20% and HIGH group is ≥20%) to evaluate subject's insulin response to glucose feeding. No subjects developed rebound hypoglycemia (<70 mg/dL) in the G trial of both group. Significantly higher blood glucose during exercise was recognized only in the G trial of LOW group. Although no significant difference was observed between the two trials of both group, cycling time to exhaustion in the LOW group tended to increase because of glucose ingestion. These results suggest that pre-exercise ingestion of glucose in East Asian student athletes does not induce rebound hypoglycemia regardless of difference in individual insulin responses. Furthermore, individuals with low insulin responses seem to improve endurance performance with glucose ingestion before exercise.
Keywords: Japanese; breakfast; exhaustion; rebound hypoglycemia; substrate oxidation.