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Does Your Muscles’ Circadian Rhythm Make Morning Workouts Better for You?

Does Your Muscles’ Circadian Rhythm Make Morning Workouts Better for You?

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Waking up early and squeezing in a workout before work may not seem like the most natural of habits for you as you’re dragging yourself out of bed, but it turns out that exercising with the sun instead of hitting the gym at night might be in your best interest after all.

New research from Northwestern University suggests that humans may respond to exercise more efficiently during natural waking hours. The study examined mice – which are nocturnal – exercising on treadmills. They found that the genes in muscles that are important for adapting to the oxygen conditions of exercise were more easily turned on at night, when mice are naturally awake.

This adaptability is controlled by a circadian clock in the muscles, which interacts with proteins called HIFs that manipulate energy metabolisms based on how much oxygen is available. For example, when we are at rest or exercising very minimally, our muscles use oxygen to create their energy. As we increase the level of intensity and perform more difficult exercises, such as sprinting, the rate at which we consume oxygen increases and it eventually runs out. This signals HIFs and muscles to switch from oxygen to sugar in order to create energy, and the sugar is converted into lactic acid. When the Northwestern scientists mutated the genes of mice to not have an internal muscular clock, the efficiency of this process decreased and the switch between using oxygen for energy to using sugar occurred at a much higher capacity of exercise. Thus, the scientists believe that exercise and oxygen efficiency may be linked to certain times of the day – in this case, normal waking hours.

These findings in mice suggest that humans likely have similar muscular clocks that determine how efficiently we use our muscles and our oxygen during different times of the day. This would most likely mean that our muscles are most efficient during daylight hours, but the study did not extend to humans and therefore no conclusions can be drawn and no advice can be given on the matter. However, researchers said that if they can find a connection in the future, it could have key applications in studying and understanding glucose metabolism in people with diabetes.

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