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Date of Award
Bachelor of Science (BS)
Department of Kinesiology
Purpose: The present study addressed two questions related to macronutrient supplementation during endurance exercise. Firstly, the effects of carbohydrate and protein co-ingestion on time trial (TT) performance were compared to carbohydrate alone. Secondly, the effects of isolated protein ingestion on TT performance were compared to a placebo.
Methods: Six trained cyclists (Age: 22 ± 1 years; Height: 167 ± 12 cm; Weight: 60 ± 10 kg; VO2max: 62 ± 7 ml/kg/min) completed four experimental trials, consisting of constant-load cycling for two hours (55% Wmax) immediately followed by a 30-km simulated time trial. During the trials, subjects consumed one of four experimental beverages at regular intervals during exercise: a non-caloric placebo (PL), a protein-only beverage (PR: 15 g/hr), a carbohydrate-only beverage (45 g/hr), or a carbohydrate and protein beverage (CP: 45 g/hr CHO + 15 g/hr PRO). Physiological measurements (VO2, VE, HR, RER, blood glucose, and blood lactate) and subjective measurements (GI distress and RPE) were assessed throughout both the constant-load and TT exercise phases. Trials were completed in a randomly-counterbalanced order. Mean ± 90% confidence intervals were calculated for all measures, and magnitude-based qualitative inferences were used to assess treatment effects.
Results: In comparison to PL (62.8 ± 8.1 min), both CHO and CP provided ‘possible’ benefits in TT performance (58.9 ± 6.5 min; 59.2 ± 9.4 min respectively) while no clear effects of PRO on performance were observed (61.0 ± 8.0 min). Furthermore, CP had no clear effect on performance versus CHO.
Conclusions: In our sample, the addition of protein to a moderate-dose of carbohydrate did not result in meaningful improvements in time trial performance versus carbohydrate alone. Similarly, protein consumption alone provided no ergogenic effects versus a placebo.
Hurst, Jonathan B., "Macronutrient Supplementation for Endurance Athletes" (2016). Senior Honors Projects, 2010-current. 218.