Insights into exercise timing to regulate circadian clocks and phenotypes

Abstract

Summary: Circadian clocks consist of the central clock in the suprachiasmatic nucleus (SCN) and the peripheral clocks in the peripheral tissues and provide endogenous control of physiological functions. Zeitgebers, such as light-dark cycles, exercise, and feeding, entrain the circadian clocks, and proper exposure to such zeitgebers is important for health. Exercise has substantial effects on circadian rhythms. Mouse studies strongly argue that exercise affects the peripheral clock but not the central clock. On the other hand, human studies have shown that exercise affects the melatonin rhythm, which is generally considered to reflect the central clock. From these results, it is plausible that exercise may cause the melatonin rhythm to deviate from the oscillations of the central clock. The regulatory mechanism is unknown. Here, we propose that exercise directly affects the pineal gland, which lies outside the blood-brain barrier, resulting in exercise-induced changes in the melatonin rhythm independent of the central clock.

Keywords

• Exercise timing
• Circadian clocks
• Phenotypes
• Zeitgebers
• Entrainment
• Peripheral clocks