Circadian Muscle Clock

Have you noticed that there a best time of day to hit the gym? Is your best time different from your buddy's? What you've known about for a long time has only recently come to be understood as the “circadian clocks” in your muscle tissues.

Scientists at Northwestern Medicine scientists have discovered your muscle's metabolic response and energy efficiency varies upon the time of day.

"Oxygen and the internal clock are doing a dance together inside muscle cells to produce energy, and the time of day determines how well that dance is synchronized," said senior author Dr. Joseph Bass. "The capacity for a cell to perform its most important functions, to contract, will vary according to the time of day."

The finding in mice sheds light on the time-of-day differences in muscle's ability to adapt to exercise and use oxygen for energy. Muscle cells are more efficient during an organism's normal waking hours, the study found.

All cells in the body, including those in muscle, contain a clock that determines how cells adapt to changes in the environment and activity across the 24 hours. The researchers examined mouse muscle fibers and tissues for expression of genes that are important for exercise. Some more research is needed before the finding can be translated into workout advice.

The study found that when mice, which are nocturnal, are exercised during the night, their muscles are better at turning on genes to help them adapt to exercise. Since these genes also exist in humans, this suggests humans may also be able to respond better to exercise during the daytime. Usually when we rest or do non strenuous exercise, our muscles consume oxygen to make energy. When we amp the exercise up a bit, we consume oxygen faster and quickly run out.

"We're not saying we can tell athletes when they should work out," said senior author Dr. Joseph Bass, "but in the future, perhaps, you may be able to take advantage of these insights to optimize muscle function."


The scientists are excited not just about what the discovery means for your exercise regimen, but also what it portends for diabetes research. At its simplest, diabetes is a failure of muscle to consume glucose, which in turn controls blood sugar levels. By learning how to hack the muscle clock we may learn how to provide a new way to eliminate excess glucose and treat diabetes.