Locomotor exercise and circadian rhythms in mammals

The timing of locomotor activity is a major rhythmic output of the mammalian circadian system but both spontaneous and induced exercise can also themselves impact on circadian rhythms across levels of organisation and in multiple tissues, including both the brain and periphery. This review briefly summarises historical research on the influences of locomotor activity and its correlates on circadian function and then discusses recent advances in this area. Locomotor exercise can acutely alter circadian phase, both of overt behavioural rhythms and in peripheral tissues, and can stably entrain rhythms in behaviour driven by the hypothalamic master circadian pacemaker in the suprachiasmatic nucleus (SCN). Locomotor activity potently and acutely suppresses both electrical activity and clock gene expression in the master circadian pacemaker of the hypothalamus, though mechanistically how this is achieved is still unclear, as are the effects of locomotor activity in diurnal species, including humans. © 2018 Elsevier Ltd