Acute Effects of Different Melatonin Doses on Performance and Psychophysiological Responses During Exhaustive Cycling Exercise: A Double-Blind Crossover Study.

No significant differences in time to exhaustion were observed between melatonin doses and placebo during exhaustive cycling exercise.

• Fifteen physically active but cycling-inexperienced men aged 18-35 years participated in the study.
• Participants ingested placebo or melatonin at 5, 12.5, or 20 mg approximately 30 min before exercise.
• Exercise was performed at 80% of the anaerobic threshold (AnT) determined by an incremental test.
• Time to exhaustion (TLim) was the primary performance outcome and showed no significant differences between conditions.
• Effect sizes were described as small with no evidence of a dose-response relationship across melatonin conditions.

No significant differences were found in physiological variables between melatonin conditions and placebo.

• Heart rate, peripheral oxygen saturation, blood lactate concentration, and blood glucose were assessed before, during, and after exercise.
• Only main effects of time were detected, reflecting expected exercise-induced responses.
• Baseline values were comparable among all sessions.
• Effect sizes for between-condition differences were small across all physiological measures.

Ratings of perceived exertion did not differ significantly between melatonin doses and placebo.

• Ratings of perceived exertion were assessed before, during, and after exhaustive cycling exercise.
• No significant between-condition differences were observed for this psychophysiological variable.
• Only main effects of time were detected, consistent with expected responses to progressive exhaustive exercise.
• These findings indicate melatonin did not modulate psychophysiological responses at any tested dose.

The study employed a double-blind, randomized, placebo-controlled, crossover design to test acute melatonin supplementation effects.

• Participants completed four exhaustive exercise sessions corresponding to placebo and three melatonin doses (5, 12.5, or 20 mg).
• Participants were physically active but cycling-inexperienced men, aged 18-35 years (n=15).
• An incremental test was used to determine each participant's anaerobic threshold for individualized exercise intensity prescription.
• Melatonin or placebo was administered approximately 30 min before each exercise session.

Acute melatonin administration at doses of 5 to 20 mg produced no ergogenic effects in healthy, physically active, cycling-inexperienced males.

• No dose-response relationship was observed across the 5, 12.5, and 20 mg melatonin conditions for any outcome measure.
• Findings were consistent across performance, physiological, and psychophysiological outcomes.
• Results applied specifically to prolonged, individualized cycling exercise performed at 80% of the anaerobic threshold.
• The authors concluded that these doses do not alter physiological and psychophysiological responses during prolonged individualized cycling exercise.