Marrin, K., Drust, B., Gregson, W., Morris, C., Chester, N., & Atkinson, G. (2010). Positive relationship between endogenous melatonin and core temperature responses to exercise. Presentation 934 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

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This study examined the relationship between exercise-related responses of salivary melatonin and core body temperature measured at different sites in the morning and afternoon. At 08:00 and 17:00 hours, males (N = 7) completed 30 minutes of cycling at 70% peak oxygen uptake followed by 30 minutes of recovery. Salivary melatonin levels were measured at baseline, 15 minutes into the exercise, immediately post-exercise, and following 30 minutes of recovery. Esophageal, rectal, intestinal, and skin temperatures were monitored during trials.

Melatonin was generally but not significantly higher at 08:00 than 17:00 hours whilst core body temperature was significantly lower during the morning trials compared to the afternoon. This difference was much smaller for esophageal temperature compared to intestinal temperature and rectal temperature. Melatonin, core body temperature, and skin temperature all increased with exercise but the standardized effects of exercise were smaller for melatonin than for core body and skin temperature. The within-subject correlations between esophageal temperature and melatonin were r = 0.65 and r = 0.67 in the morning and afternoon respectively. Correlations between core body temperature and melatonin were also positive for the other core temperature sites, irrespective of time of day. The correlation between skin temperature and melatonin was not significant in the morning and r = 0.65 in the afternoon.

Implication. Circadian rhythms in endogenous melatonin and core temperature are inversely related at rest. Exercise mediates a parallel acute increase in both variables. Exercise effects are relatively more pronounced on core body temperature than on melatonin, suggesting that melatonin is a more stable marker of circadian timing.

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