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BACKGROUND: Nutrient timing is an effective means of augmenting endurance exercise training and performance. Previous studies report that pre-exercise feeding can influence exercise metabolism up to 4 hours post-prandial. However, this timeline has been confirmed during waking hours only; little is known about how sleep within the post-prandial period may influence metabolism during subsequent exercise. This question is relevant to the endurance competitor, as race start-times often occur in early morning, limiting the opportunity for optimal feeding prior to competition without disrupting sleep or risking gastrointestinal distress. PURPOSE: To investigate the influence of a small, nutrient dense, pre-sleep chocolate milk (CM) beverage on morning metabolism and 10-km running performance in female athletes. METHODS: In a crossover design, twelve competitive female runners (age, 30 ± 7 yrs; VO2peak, 53 ± 4 ml·kg−1·min−1) ingested either pre-sleep CM or a non-nutritive, flavor-matched placebo (PL) ~30 min before sleep and 7-9 hrs before a morning performance running trial. Following initial appetite assessment (visual analogue scales) and resting metabolic rate (RMR), serum glucose (GLU) and lactate (LAC) measurements, the performance trial included a warm-up and three 5-min incremental loads at 55, 65, and 75% VO2peak (to measure respiratory exchange ratio (RER), GLU and LAC), followed by a 10-km treadmill time trial (TT). Paired t-tests, ±90% confidence intervals, and magnitude-based inferences were used to determine differences in means. Significance was accepted at P < 0.05. RESULTS: Relative to PL, CM showed a 'likely small decrease' in perceived hunger (P = 0.041, -22.3% mean effect), and a 'likely small increase' in RMR (P = 0.049, 4.8% mean effect), resting GLU (P = 0. 081, 3.7% mean effect), and RER at 55, 65, and 75% VO2peak (P = 0.115, 0.194, 0.164 and 2.1%, 1.6%, 1.4% mean effect, respectively). Exercise GLU revealed subtle, and unique trends following CM compared to PL. Specifically, GLU was 'possibly increased' during exercise at 65% VO2peak (P = 0.358, 2.0% mean effect) and 'likely trivially decreased' at 75% VO2peak (P = 0.561, -1.0% mean effect) following CM compared to PL. No differences in resting or exercise LAC, or 10-km TT performance (PL: 52.8 ± 8.4 mins versus CM: 52.8 ± 8.0 mins, P = 0.987, -0.1% mean effect, 'most likely trivial' decrement to performance following CM compared to PL) were noted between treatments. CONCLUSIONS: Nighttime supplementation of CM results in acute enhancement to morning metabolism via increased carbohydrate utilization during exercise, but has no apparent effects on 10-km running performance. These results suggest that the nighttime feeding timeline, specifically sleep imposed within the post-prandial period may extend tangible effects to metabolism to over 8 hours out from meal ingestion.
A Thesis submitted to the Department of Nutrition, Food and Exercise Sciences in partial fulfillment of the requirements for the degree of Master of Science.
Includes bibliographical references.
Michael J. Ormsbee, Professor Directing Thesis; Lynn B. Panton, Committee Member; Robert J. Contreras, Committee Member.
Florida State University
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