A Pre-Exercise Dose of Melatonin Can Alter Substrate Use During Exercise

Notwithstanding the lack of exercise research, several reviews have championed the use of melatonin to combat metabolic syndrome. Therefore, this study compared substrate utilization during a 30-minute (min) graded exercise protocol following the ingestion of either 6 mg melatonin (M) or a placebo (P). Participants (12 women, 12 men) performed stages 1-5 of the Naughton graded exercise protocol (6 min per stage). The protocol was repeated 4 times (2x M, 2x P) at the same time of day with one week separating each session. Expired gases were monitored, VO₂ and respiratory exchange ratio (RER) output was provided every 30s. Total, carbohydrate (CHO), and fat energy expenditures were obtained from the RER values using the formulae of Lusk. The VO₂ at which CHO accounted for 50% of the total caloric expenditure was calculated by a VO₂: RER regression line. Additionally, the energy derived was calculated by multiplying VO₂ and the respective energy expenditures. Then, the total, CHO, and fat energies consumed during the 30 min of exercise were determined by calculating the area under the kJ/min: time curve using the trapezoid rule. The final data for the two similar trials were averaged and a paired-T test was used for statistical comparison. The average VO₂ for 50% CHO usage was significantly lower following M (0.84 ± 0.54 l·min^-1) than after P (1.21 ± 0.52 l·min^-1). Also, average CHO kJ for M (627 ± 284) was significantly (p < 0.004) greater than P (504 ± 228), and accounted for a significantly greater contribution of total kJ consumed (M = 68% ±15 vs. P = 61% ± 18). Ingestion of melatonin 30 min prior to an aerobic exercise bout elevates CHO use during exercise.