Estimates vary from 10% to 50%, says Panteleimon Ekkekakis, a professor of kinesiology at Iowa State who has been studying the psychophysiology of exercise.

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The study is published in the International Journal of Psychophysiology.

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In a study published earlier this month in the International Journal of Psychophysiology, he and his colleagues monitored the brain activity of 79 female and 70 male students while they performed a letter-identifying exercise.

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