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Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Date of Award

Spring 2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Department of Kinesiology

Advisor(s)

Michael J. Saunders

Nicholas D. Luden

Christopher Joseph Womack

Abstract

Purpose: Carbohydrate (CHO) ingestion during exercise enhances performance in short endurance events (~ 1 hr) due to neural influences, as demonstrated by the efficacy of CHO mouth-rinsing during cycling. However, the magnitude of these neural effects may be blunted following pre-exercise CHO feedings. This study examined whether the glycemic index (GI) of a pre-exercise meal affected time-trial (TT) performance in cyclists using a CHO mouth-rinse during exercise. Methods: Eight cyclists (age: 24 ± 6 yr; VO2max: 61 ± 8 ml×kg-1×min-1) completed 4 exercise trials, consisting of 15 min of constant-load cycling followed by a simulated 30-km TT. Treatments were: a) L-CHO: low GI CHO beverage pre-exercise (1.5 g×kg-1 CHO, 120 min prior), CHO mouth rinsing during exercise (6.4% maltodextrin solution), b) H-CHO: high GI CHO beverage (1.5 g×kg-1 CHO) pre-exercise, CHO mouth rinsing during-exercise, c) PL-CHO: placebo beverage pre-exercise, CHO mouth rinsing during exercise, and d) PL-PL: placebo beverage pre-exercise, placebo mouth rinsing during exercise. Blood glucose was measured before beverage consumption and at 30 and 120 min following ingestion. Physiological measurements (VO2, VE, RER, HR, RPE, glucose, lactate, and gastrointestinal distress) were assessed during constant-load cycling and the TT. Magnitude-based qualitative inferences were used to assess differences in responses between trials. Results: Blood glucose differed among treatments 30 min post-feeding (H-CHO > L-CHO > PL-CHO = PL-PL), and was lower in H-CHO versus PL-CHO and PL-PL during subsequent exercise. Compared to PL-CHO, TT performance was faster in both L-CHO (-0.5 ± 0.8 min; “likely” beneficial) and H-CHO (-0.7 ± 0.7 min; “likely” beneficial), with no systematic differences between L-CHO and H-CHO. However, none of the 3 mouth rinse trials were clearly different from the PL-PL trial. Conclusions: When using a CHO mouth rinse during exercise, CHO ingestion 2 hr prior to cycling enhanced TT performance versus exercise in the fasted state. The GI of the pre-exercise feeding did not systematically affect TT performance in cyclists using a CHO mouth-rinse. However, the impact of these findings is confounded by the lack of performance differences versus a control trial without CHO before or during exercise.

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