The Influence Of A Whey Protein Preload Prior To Carbohydrate Consumption On Cycling Performance

INTRODUCTION: The consumption of carbohydrates during a bout of endurance exercise has been shown to promote a glycogen sparing effect and lead to an improvement in exercise performance. The consumption of whey protein prior to a prolonged bout of endurance exercise may augment insulin secretion and further spare muscle glycogen. PURPOSE: To examine if a whey protein solution consumed as a preload prior to a glucose bolus influenced performance and metabolic responses during a cycling performance trial. METHODS: Ten recreationally trained cyclists and triathletes completed two experimental trials. Each participant was required to perform two separate cycling performance tests, which consisted of cycling for 30 min at 90% lactate threshold, followed by a 30 min time trial. Participants consumed a whey protein isolate preload (0.7 g/kg/LBM) or a placebo 20 min prior to the consumption of a glucose beverage (0.9 g/kg/LBM). The glucose beverage was consumed 10 min prior to the cycling performance test. During both trials, plasma glucose, c-peptide, insulin, glucagon, and NEFA concentrations were measured. RESULTS: There were no significant differences in overall time trial performance (WP 16.8 ± 0.34 km; PL 17 ± 0.4 km; p = .346). WP stimulated a significant increase in plasma insulin concentrations at time point 0 (WP = 222.88 ± 45.1 pg/ml; PL = 85.95 ± 45.1 pg/ml; p = .047) compared to the placebo trial. Despite an increase in plasma insulin, there were no significant timepoint differences for plasma glucose. WP stimulated a significant increase in plasma glucagon concentrations for timepoint -10, 0, 15, 30, 45, and 60 when compared to the PL trial (all values p < .05). CONCLUSION: Although there were significant alterations in plasma insulin concentration due to the consumption of the whey protein isolate preload, this did not influence overall cycling performance or substrate utilization. Funding Source: National Strength and Conditioning Association – GNC Sport Nutrition Grant