Nighttime Feeding and Morning Endurance Performance

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.

Inclusion criteria

• Female
• Between the ages of 18 and 40 years old
• Consistently use oral contraceptives (greater than 2 months) or be considered eumenorrheic without oral contraceptive use
• 'Moderately trained,' defined as a weekly mileage ≥ 25 miles for at least 6 months, and a VO2max ≥ 45 ml/kg/min

Exclusion criteria

• Lactose intolerant
• Smokers
• Uncontrolled thyroid conditions
• Uses anti-inflammatory drugs or any dietary supplements intended to improve performance
• Have musculoskeletal injury that could limit performance