Glucose and Fructose Ingestion following High Intensity Exercise does not Affect Subsequent Exercise Capacity
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Previous studies have suggested that ingestion of glucose+fructose prior to and during long duration endurance exercise may benefit performance more than ingestion of glucose alone. The purpose of this study was to investigate the effects of glucose+fructose ingestion on short duration high intensity exercise capacity. Eight trained malecollege athletes performed three randomized experimental trials consisting of a 20 minute run at 90% VO2 max, a 5 minute recovery period, and a time-to-exhaustion (TTE) run at 90% VO2 max. During the recovery period, subjects ingested a beverage containing glucose + fructose (G+F), glucose only (GLU), or placebo (PLA) matched for taste and electrolyte content. Carbohydrate (CHO) beverages each contained ~20g of carbohydrate. Subjects’ blood glucose was measured immediately before and after each run period. Heart rate (HR) and Rating of Perceived Exertion (RPE) was recorded every 2 minutes during TTE. Blood glucose levels standardized to baseline values were significantly greater in the G+F trial both prior to and after TTE relative to PLA (P<0.05). However, there was no significant difference in HR, RPE, and TTE performance (G+F: 22.15±5.88min, GLU: 18.27±4.18min, PLA: 17.75±3.26min) between trials (P>0.05). Results from this study suggest that ingestion of glucose and fructose following high intensity exercise lasting 20 min does not enhance subsequent performance capacity more than glucose alone or placebo. Future studies are needed to determine if a stronger reliance on endogenous versus exogenous CHO in the early stages of high intensity exercise can account for the lack of performance benefits seen in this study.