Influence of Exercise Time of Day on Salivary Melatonin Responses

Abstract

Sleep deprivation may have changes in cognition, pain, mood, metabolism, and immunity, which can ultimately create negative consequences on athletic performance. Melatonin is thought to induce sleepiness due to its synchronization with the circadian rhythm. PURPOSE: The purpose of this study was to evaluate the influence of exercise time of day on salivary melatonin (s-Mel) responses. METHODS: Ten regularly exercising, males (age 20.7 ± 0.7 yr; height 1.74 ± 0.04 m, mass 73.6 ± 11.4 kg, maximal oxygen consumption [VO2max] 56.4 ± 4.4 ml/kg/min-1) completed a VO2max using an incremental protocol on a treadmill. In a randomized, crossover design, subjects completed three protocols: morning exercise (09:00 h), afternoon exercise (16:00 h), and no exercise (control) at least 5 days apart. For each exercise session, subjects performed 30 min of steady-state running at 75% of VO2max following a 5 min warm-up. Saliva was collected via a passive drool into 2 ml polypropylene conical tubes at 20:00 h, 22:00 h, and 03:00 h following all sessions. RESULTS: No significant differences existed in the s-Mel levels for exercise time of day. A trend found morning exercise produced a higher concentration of s-Mel than afternoon exercise (p = 0.074). The 20:00 h collection time was significantly higher than the 03:00 h collection (p = 0.001). Additionally, s-Mel levels were significantly (p = 0.018) greater for the 20:00 h collection time compared to the 22:00 h collection, and 22:00 h was greater than 03:00 h (p = 0.038). CONCLUSION: It appears that exercise time of day did not affect s-Mel levels.Table 1: s-Mel Levels, (pg/mL), Mean ± SDSupported by: NEACSM Undergraduate Research Grant