The Best Time of Day to Work Out

13Increasingly, scientists are inviting athletes into the lab to investigate the ef­fects of body rhythms on athletic performance. Most exercise-related rhythms, including heart rate, manual dexterity and reaction time, peak in the afternoon and evening. The result is “a window of opportunity between noon and 9 p.m., when we’re likely to be at our physi­cal—if not mental—best,” says exercise physiologist Tom Reilly of the Liverpool John Moores University in England.
Numerous studies of swimmers, soccer play­ers, rowers and long jumpers suggest there is in­deed an afternoon performance edge. “The ma­jority of athletes in these studies performed better later in the day,” says Dr. Reilly. And only two Olympic track and field records since 1945 have been broken before noon.

There also seems to be a psychological compo­nent to the peak performance phenomenon. At least one study indicates that “perceived exer­tion,” meaning how difficult a workout feels, is lowest in the evening. Reilly had 10 women com­plete a weight training circuit in the morning, then again in the evening. Even though they lifted the same amount of weight both times, they reported that the morning workout was more difficult.

You can determine your own peak perfor­mance time by plotting your temperature every couple of hours for several days in a row. lit will vary by as much as 1.5° throughout the day.) “Theoretically,” says Reilly, “you’ll perform best during the period three hours before and after your daily temperature high-4 p.m. or 5 p.m. for most people.” If you’re a morning person, expect your peak to be an hour or two earlier than aver­age; night owls, on the other hand, peak slightly later than the norm. (As we age, peak perfor­mance time shifts toward the morning, perhaps because older people tend to go to bed and get up earlier, which moves their body clocks ahead.)

Of course, genetic ability, training and motiva­tion also influence how well we perform. But be­ing aware of your body rhythms can make a dif­ference. One study of a dozen swimmers who worked out on an arm and shoulder machine found that when they exercised at the wrong time of day—too long before or after their circa­dian peaks—their performance dipped 10%, the equivalent of working out on three hours of sleep or after drinking a couple of glasses of wine.
It makes sense, then, to harness your circadian rhythms if you’re looking to gain an edge on the track or playing field. If you must compete in a minimarathon at 7 a.m. and you don’t usually rise until 8 a.m., try getting up a few hours earlier for several weeks beforehand, in order to shift your circadian peak toward morning. If your schedule (or personality) mandates a morning workout, warm-up exercises and stretches are even more important than they are later in the day (body temperature is lowest when you awaken). And people with heart trouble should avoid vigorous workouts before noon, when heart attacks are most common. The heart-healthy, of course, should feel free to work out at any time of day.—MARY GARNER GANSKE

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