Study: How Exercising In Morning Impacts Body Differently Than Fitness At Night

COPENHAGEN, Denmark — Whether you’re an early-bird or a night-owl, getting regular exercise is still generally a good idea at some point in your schedule. It turns out, however, that when you log your workout may affect your body differently. A recent study shows that the health benefits of exercise differ depending on the time of day that you get in your workout routine.

Researchers from the University of Copenhagen and the University of California, Irvine discovered these significant differences by placing mice on a treadmill at various times of day. Mice are nocturnal animals so their circadian rhythm runs in the opposite direction of humans. Their morning starts when it gets dark and their night starts when it gets light.

“There appears to be rather significant differences between the effect of exercise performed in the morning and evening, and these differences are probably controlled by the body’s circadian clock,” says co-author Jonas Thue Treebak, an associate professor from the Novo Nordisk Foundation Center for Basic Metabolic Research, in a release.

The authors found that when mice are on a morning exercise schedule, the cells in their muscles are able to process fat and sugar better. That being said, they also noted that running on the treadmill in the evening caused mice to use more energy (burn more calories) for longer periods of time.

“Morning exercise initiates gene programs in the muscle cells, making them more effective and better capable of metabolizing sugar and fat. Evening exercise, on the other hand, increases whole body energy expenditure for an extended period of time,” says Treebak.

This finding is especially interesting to the research team because it seems to indicate the time of day that people with severe overweight or type-2 diabetes might be able to maximize exercise gains. Still, these differing effects make it difficult for the researchers to determine when it’s better in general to exercise.

“On this basis we cannot say for certain which is best, exercise in the morning or exercise in the evening,” says Treebak. “At this point, we can only conclude that the effects of the two appear to differ, and we certainly have to do more work to determine the potential mechanisms for the beneficial effects of exercise training performed at these two time-points.”

The research team already plans to perform similar studies in humans.

The study is published in Cell Metabolism.

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