Pre-Exercise Ingestion of High- vs. Low-Glycemic Index Food: Effects on Cycle Time Trial Performance

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Dr. Maureen Dunn, Hope College

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The purpose of this study was to determine whether the administration of a high-GI food immediately prior to exercise had the same effect on cycle time trial performance as a low-GI food administered 45 minutes before exercise. Nine volunteers (males, n=5; females, n=4) recruited from a Hope College Health Dynamics class completed three 20km cycle time trial rides (70% VO2max), one week apart in a counterbalanced manner. One trial included the ingestion of a high-GI snack immediately prior to exercise, another trial included the ingestion of a low-GI snack 45 minutes before exercise, while a third trial served as a control with no food. Time trial performance did not improve significantly in any of the three trials (C=37.472 ± 1.704min, H=38.657 ± 1.625min, L=37.493 ± 1.622min, P>0.05). Blood glucose (C=93.56 ± 16.37 mg/dL, H=99.67 ± 24.59 mg/dL, L=96.44 ± 20.13 mg/dL) and lactate (C=9.50 ± 2.94 mmol/L, H=9.91 ± 3.97 mmol/L, L=8.72 ± 4.54 mmol/L) concentrations were not significantly different between groups; however, there was a significant difference in perceived stomach fullness between the high-GI and the low-GI groups (p=.043), as well as between the High-GI and control groups (p=.008). Results indicate that the composition of a pre-exercise meal will not affect performance in 20 km time trial performance.

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