Save Tough Workouts for Later in the Day
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Even if you're typically a morning exerciser, you may want to wait until after work to do high-intensity cardio or sports that require fast footwork, according to a new study. Researchers tested elite college jumpers and sprinters early in the morning and found they had poorer performance during dynamic, multifunctional exercises, specifically because of the predawn hour.

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The reason: Their hormone levels of melatonin were roughly eight times higher right after waking up. "These higher melatonin levels may mean that the athletes were less physiologically awake," says Dr. Maren Fragala, co-author of the study. She suggests saving agility-related exercise, such as intervals or sports like tennis and basketball, until later in the day (previous studies have shown that late afternoon may be the best time for most people's internal clock).

Just make sure to get your workout in before 9 PM, when your body's levels of melatonin begin to rise again in anticipation of another night's sleep.