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The circadian rhythm is the body’s 24-hour cycle of biological, hormonal, and behavioral patterns that, when disrupted, has profound implications for human healthspan. Findings from a recent study suggest that a single bout of exercise can reset the circadian clock in the skeletal muscles of mice.

The circadian clock coordinates gene expression in nearly all cells in a time-dependent manner. Cues from the environment, known as zeitgebers, can alter the circadian clock in a process known as entrainment. Light acts as the primary zeitgeber, but activity, stress, and eating also affect circadian timing. Exercise affects body temperature, heart rate, and many other metabolic parameters and might also entrain the circadian clock.

The current study investigated whether exercise would act as a zeitgeber for the circadian clock in the skeletal muscles of mice. Transgenic mice completed a sixty-minute bout of moderate‐intensity exercise at different times during their rest or active periods. The authors of the study observed that mice exercised during their typical rest period exhibited a shift in the muscle circadian clock. However, mice exercised during their active phase showed no effects on the circadian rhythm.

To factor out the hormonal and temperature effects of exercise, the authors developed an in vitro model system using time‐synchronized rodent muscle cells. They subjected these cells to an electrical current, to simulate muscle contractions, and measured the expression of known molecular clock‐related genes. The authors found that electrical stimulation altered the expression of clock genes, and shifted the circadian clock in a pattern similar to that observed in the mouse model system.

Taken together these findings suggest that a single bout of exercise can alter the circadian clock — making it a true zeitgeber. The specific effect of exercise on the circadian clock depends on the time when it is performed. While further studies are needed to determine if these findings translate to humans, the authors propose that shift workers might benefit from timed exercise to offset some of the negative effects of circadian disruption.

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