Exercise is considered to be a timing factor (zeitgeber) that can affect rhythm changes in skeletal muscle. The phase of the skeletal muscle clock affects the metabolism of the muscles. However, whether exercise intensity induces phase changes in oscillations of clock genes as well as clock-controlled metabolic genes remains uncertain. We aimed to assess the effects of heavy exercise on skeletal muscle clock genes and phase changes in oscillations of clock-controlled metabolic genes. The expression of clock genes Bmal1 and Clock in the skeletal muscle of rats was analyzed by real-time PCR, and the expression of clock-controlled metabolic proteins NAMPT, NAD+, and SIRT1 was analyzed by ELISA. Sprague Dawley rats were kept under a regular 12/12-h light/dark cycle. Rats in the exercise group were exposed to a downhill run of 90 min at a speed of 16 m/min and an angle of − 16°. Sampling was performed at 6-h intervals. Compared with the control group, the rhythm of Bmal1 mRNA expression in the exercise group disappeared on the first day, and the rhythm recovered on the second day; Clock mRNA expression lost its rhythmicity in 72 h. The expression of NAMPT, NAD+, and SIRT1 was lost on the first day and the second day, but the rhythm recovered on the third day. These data demonstrate that muscle contractions are sufficient to shift the phase of muscle circadian clock and clock-controlled metabolic genes, likely via changes in core clock gene expression.

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