CONSUMPTION OF A 5-MG MELATONIN SUPPLEMENT DOES NOT AFFECT 32.2-KM CYCLING TIME TRIAL PERFORMANCE

Some studies suggest that exogenous melatonin supplementation may improve athletic performance in hot humid environments because of its precooling effect. However, melatonin is also consumed as a sleep aid for its depressive effects on the central nervous system (CNS), which may hinder performance. Therefore, this study was conducted to determine whether consuming a 5-mg supplement of melatonin would affect performance in a laboratory-simulated 32.2-km cycling time trial. The time trial was conducted in a thermoneutral environment to separate CNS depressive effects of the melatonin from the cooling effects. Trained male subjects (n = 10; (V) over doto(2)max = 62.7 +/- 6.3 ml.kg(-1).min(-1); age = 25.1 +/- 4.0 years; mass = 69.9 +/- 9.1 kg; height = 176.0 +/- 7.1 cm) performed three 32.2-km time trials on an electronically braked cycle ergometer. The first trial was a familiarization. During the 2 experimental trials, subjects received in a random order either a placebo or a 5-mg melatonin supplement 15 minutes before exercise in a double-blind, crossover design. Variables were measured before exercise and at 8-km intervals. The mean 32.2-km time trial completion times for the melatonin (64.94 +/- 5.95 minutes) and placebo (65.26 +/- 6.85 minutes) trials were not different (p = 0.682). The mean time trial power output for the melatonin (190.4 +/- 40.4 watts) and placebo (190.0 +/- 45.7 watts) trials was not different (p = 0.927). Rectal temperature was not significantly different for melatonin compared with placebo (p = 0.827). These results suggest that a 5-mg melatonin supplement administered 15 minutes before exercise does not measurably impact the performance of a 32.2-km cycling time trial in a thermoneutral environment.