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Experts disagree on ideal time of day to exercise

Doctor says late afternoon workouts best bet for body

By Stephanie Smith

Doctor says late afternoon workouts best bet for body

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(CNN) -- Whether trekking on a treadmill or slicing through a pool, for many people, exercising in the morning is like drinking a cup of coffee. The early physical activity stimulates them and gives the day a strong start.

"I feel great after morning exercise," said Orlando Suarez, a 39-year-old director of special events in Los Angeles, California. "I feel very energetic, very clear. It's like I have a sustained energy throughout the day."

But one neurologist is challenging the old convention of the morning workout. In fact, Dr. Phyllis Zee of Northwestern University has a different opinion about when is the ideal time to exercise.

"The best time to work out is in the late afternoon," Zee said. "The reason for that is your muscle strength is at its peak, its highest. You're going to be less likely to injure yourself. It's also a time when people are most awake and alert."

The science behind Zee's assertion resides with delicate rhythms of the brain called circadian rhythms. According to Zee, circadian rhythms explain why working out later in the day might be more productive and beneficial.

"One of the things that circadian rhythms does is that it determines when your best performance time is," Zee said. "Your ability to perform changes throughout 24 hours."

Circadian rhythms operate like an internal clock in the body. Neuron signals are fired out by the hypothalamus [a region of the brain], controlling sleep patterns, blood pressure, even our moods.

"These are rhythms that are innate," Zee said. "They are in almost any organism, whether you are an animal or a plant, and they recur every 24 hours."

Circadian rhythms also control body temperature, a key element of a more productive workout. According to Zee, by the afternoon, body temperature is between one and two degrees warmer than in the morning, making muscles in the body more supple and lowering the risk of injury.

Another circadian expert agrees.

"Maximum body temperature happens between 2 and 4 p.m.," said Dr. Michael Vitiello, a professor of psychiatry and behavioral sciences at the University of Washington. "After that, [body temperature] starts to decline for most people.

"It all depends on whether you want to exercise in early afternoon or early evening. But we're not talking about a gigantic difference [from the peak period]."

Challenging popular notions

David Padron, a 28-year-old graphic designer in Fresno, California, finds that his afternoon workouts aren't only easier on his body but also that his performance increases, too.

"I look forward to it all day," Padron said. "I feel more relaxed. In the afternoon, I have the energy to lift 20 more pounds than in the morning."

Some health experts recommend exercising in the morning because the body's metabolism will get an early start at burning calories and sustain that higher metabolic rate during the hours after.

But for one fitness expert, that might not be enough of an argument for morning exercise.

"There is some evidence that morning exercise promotes more fat burning than other times of the day, but the difference is so small that it really wouldn't matter," said Richard Cotton, an exercise physiologist. "And if you're going to exercise inconsistently in the morning, then it's not worth it at all."

Some better than none

Recently, a government study found an alarming exercise trend among American adults. A staggering 60 percent of Americans don't exercise enough, and more than 25 percent aren't physically active at all, according to the report from the Centers for Disease Control and Prevention.

Cotton, who is also a spokesman for the American Council on Exercise, agrees that afternoon exercise might be a good way to prevent injury and get maximum performance, but said the most important thing is a consistent exercise regimen.

"In middle-aged and younger adults, it's probably not a big difference for them in terms of their exercise time," Cotton said. "It is really their lifestyle and what works for them that's really important when determining your exercise time."

Health experts agree -- it's better to exercise some than not at all. They say if people prefer to exercise in the morning, they need to spend a few more minutes warming up to stay on the path to good health.

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