Influence of Exercise Time of Day on Salivary Melatonin Responses.

Abstract

Sleep deprivation negatively affects cognition, pain, mood, metabolism, and immunity, which can reduce athletic performance. Melatonin facilitates sleepiness and may be affected by the proximity of exercise to sleep. To evaluate the influence of exercise time of day on salivary melatonin (s-melatonin) responses. Twelve regularly exercising men (age 20.75 [0.62]y, height 1.75 [0.04]m, mass 73.63 [10.43]kg, and maximal oxygen consumption 57.72 [6.11]mL/kg/min) participated in a randomized, crossover design. Subjects completed 3 protocols-morning exercise (09:00h), afternoon exercise (16:00h), and no exercise (CON)-at least 5 d apart. Exercise sessions consisted of 30min of steady-state running at 75% of maximal oxygen consumption. Saliva was collected via passive drool at 20:00, 22:00, and 03:00h following all sessions. Repeated-measures analysis of variance revealed significant time (P = .001) and condition (P = .026) effects for melatonin. Levels of s-melatonin were significantly increased at 03:00h compared with 20:00 and 22:00h for all conditions. Post hoc analyses revealed that s-melatonin at 22:00 h was significantly higher after morning exercise (16.5 [7.5]pg/mL) compared with afternoon exercise (13.7 [6.1]pg/mL) sessions (P = .03), whereas neither exercise condition significantly differed from the control (P > .05). It appears that exercising in the afternoon may blunt melatonin secretion compared with morning exercise. If sleep is an issue, morning exercise may be preferable to afternoon exercise.