Nighttime Feeding and Morning Endurance Performance

Overview

The purpose of this study is to investigate the influence of a nighttime feeding on next morning running performance, hydration status, and exercise metabolism in female endurance athletes. Specifically, the effect of a chocolate milk beverage will be examined versus a non-nutritive, flavor-matched placebo. The investigators hypothesize that the nighttime consumption of chocolate milk, a whole food complex, will result in improved next morning running performance versus placebo. Secondarily, the investigators hypothesize that any potential positive performance outcomes from the chocolate milk treatment may be due to an enhanced pre-exercise hydration status or improved exercise metabolism.

This study will be interventional in nature and employ a crossover, randomized, double-blinded approach. This study will include a maximal oxygen uptake test and three trials: one familiarization trial, and two experimental trials. The familiarization will serve as a practice test to minimize any training effects between experimental trials. The experimental trials will be completed within a 2-week period determined by the luteal phase of the menstrual cycle (days 15-28 of the menstrual cycle, with day 1 being the first day of menstruation). A minimum of 48-72 hours will be provided between testing days. Experimental trials will consist of baseline testing (height, weight, urinalysis, resting metabolic rate), followed by a treadmill performance protocol. Participants will complete a 3-stage incremental exercise test (at 55%, 65%, and 75% of maximal oxygen uptake respectively). Metabolic data will be collected during this time. Participants will then complete a 10-kilometer running time trial in which markers of intensity are monitored at various time points (blood glucose, blood lactate, heart rate, rating of perceived exertion). Participants and primary researchers will be blinded to all time and speed data. Distance will be the only known measure of progress. Additional blood, urine, and body weight measures will be taken immediately post exercise.