Morning exercise has very different effects on metabolism than the same workout later in the day, an ambitious new animal study of exercise timing showed.
The study, which involved healthy lab mice jogging on tiny treadmills, mapped hundreds of disparities in the numbers and activities of molecules and genes throughout the rodents' bodies, depending on whether they ran first thing in the morning or deeper in the evening.
Many of these changes related to fat burning and other aspects of the animals' metabolisms. Over time, such changes could substantially influence their disease risks and well-being. And though the study featured rodents, its findings likely have relevance for any of us who wonder if it is better to work out before work, or if we might get as much - or more - health benefit from after-hours exercise.
So, for the new study, published this month as the cover article in Cell Metabolism, an international consortium of researchers decided to try quantifying almost every molecular change related to metabolism that occurs during exercise at different times of day.
Using healthy, male mice, they had some jog moderately on wheels for an hour early in the day and others run the same amount in the evening. An additional group of mice sat on locked wheels for an hour during these same times and served as a sedentary control group.
Overall, the differences in molecular profiles between morning workouts (in mouse terms) and those later in their days tended to signal greater reliance on fat than blood sugar to fuel the early exercise. The opposite occurred when the mice ran in their evening. If those patterns held true in people, it might suggest morning exercise contributes more to fat loss, whereas late-day workouts might be better for blood-sugar control.
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