Circadian Rhythm, Exercise, and Heart.

Circadian rhythm is an evolutionarily conserved mechanism from archaea to human. To deal with the day-night changes in the environment on earth, circadian rhythm modulates the biological function to coordinate an appropriate timing for each process. Circadian rhythm and exercise have important impacts on each other. Exercise is a strong entrainment signal for mammalian circadian clock. 1 Proper exercise can have a significant circadian phase-shifting effect and affect the sleep and wake schedule in human. 2 Disruption of the circadian rhythm also has significant influences on the exercise function. The circadian gene CLOCK mutation in mice results in significantly reductions in muscle power and exercise endurance. 3 Moreover, CLOCK mutation also disturbs muscle myofiber and mitochondrial functions. 4 The close interactions between circadian rhythm and exercise are further strengthened by the findings that the diurnal variations of musculoskeletal functions and the impact of the circadian clock on energy metabolism and bone. 5