Low vs. High Glycemic Index Carbohydrate Gel Ingestion During Simulated 64-km Cycling Time Trial Performance

Abstract

Earnest, C.P., S. Lancaster, C. Rasmussen, C. Kerksick, A. Lucia, M. Greenwood, A. Almada, P. Cowan, and R. Kreider. Low vs. high glycemic index carbohydrate gel ingestion during simulated 64-km cycling time trial performance. J. Strength Cond. Res. 18(3):466–472. 2004.—We examined the effect of low and high glycemic index (GI) carbohydrate (CHO) feedings during a simulated 64-km cycling time trial (TT) in nine subjects ([mean ± SEM], age = 30 ± 1 years; weight = 77.0 ± 2.6 kg). Each rider completed three randomized, double blind, counterbalanced, crossover rides, where riders ingested 15 g of low GI (honey; GI = 35) and high GI (dextrose; GI = 100) CHO every 16 km. Our results showed no differences between groups for the time to complete the entire TT (honey = 128 minutes, 42 seconds ± 3.6 minutes; dextrose = 128 minutes, 18 seconds ± 3.8 minutes; placebo = 131 minutes, 18 seconds ± 3.9 minutes). However, an analysis of total time alone may not portray an accurate picture of TT performance under CHO-supplemented conditions. For example, when the CHO data were collapsed, the CHO condition (128 minutes, 30 seconds) proved faster than placebo condition (131 minutes, 18 seconds; p < 0.02). Furthermore, examining the percent differences and 95% confidence intervals (CI) shows the two CHO conditions to be generally faster, as the majority of the CI lies in the positive range: placebo vs. dextrose (2.36% [95% CI; -0.69, 4.64]) and honey (1.98% [95% CI; -0.30, 5.02]). Dextrose vs. honey was 0.39% (95% CI; -3.39, 4.15). Within treatment analysis also showed that subjects generated more watts (W) over the last 16 km vs. preceding segments for dextrose (p < 0.002) and honey (p < 0.0004) treatments. When the final 16-km W was expressed as a percentage of pretest maximal W, the dextrose treatment was greater than placebo (p < 0.05). A strong trend was noted for the honey condition (p < 0.06), despite no differences in heart rate (HR) or rate of perceived exertion (RPE). Our results show a trend for improvement in time and wattage over the last 16 km of a 64-km simulated TT regardless of glycemic index.