General: Looking for peak performance? Check your watch first

If your favorite pitcher slept in until 3 p.m. before his night game, don't bet on him throwing a no-hitter.

That's because his body thinks it's still "late morning" when the game starts at 7:30.

According to a recent study from the University of Chicago, athletes do their best at night, or at least when their endocrine system thinks it is.

Your pitcher's bad day at the mound may have less to do with his attitude and more to do with the failure of his hormones to kick in. If there's no jump in his blood serum levels of cortisol and thyrotropin, there may be no jump in his curve ball.

Researchers found that physiological responses regulating energy use and some hormones differs according to when in the day exercise is performed.

"The effects of exercise we observed may explain how some times of day could be better than others for regular exercise or athletic performance, as we might expect from anectdotally reported variations in peak athletic performance," said Orfeu Buxton, Ph.D., a post-doctoral fellow in endocrinology at the University of Chicago. "We found strong evidence for substantial changes in glucose metabolism and an array of hormonal responses to one-hour, high-intensity exercise, dependent on the timing of the exercise.

"Circadian rhythms, generated by our 24-hour internal clock, appear to play an important role in the complex response to exercise," he said in a statement released by the University of Chicago Medical Center.

Subjects who exercised at night had much larger drops in glucose levels than at other times of day. Large increases in the levels of two hormones important for energy metabolism, cortisol and thyrotropin, were observed. But exercise at other times of day had much smaller effects.

For the study, 40 healthy men, between the ages of 20 and 30, were divided into five groups. Four groups exercised vigorously for one hour on a stair-stepper in the morning, afternoon, evening or night. A control group did not exercise.

A standard marker, the timing of melatonin secretion, was used to determine the timing of each individual's daily rhythm, his circadian "clock time."

Blood levels of the "circadian hormones," melatonin, cortisol and thyrotropin were compared against blood levels for the same time of day in the resting control subjects.

"Many circadian rhythms, such as heart rate, oxygen consumption, and cardio-pulmonary function play a role in athletic performance. Rhythmic patterns of hormonal secretion provide internal temporal organization essential to the coordination of physiological processes. Physical exercise is associated with marked metabolic changes and can elicit a variety of neuroendocrine responses," a press release from the University of Chicago stated.

Medical disclaimer: It is not the intention of this article to provide specific medical advice, but rather to provide users with information to better understand their health and their diagnosed disorders. Specific medical advice should not be provided or accepted without a thorough physical examination. Consult with a qualified physician for answers to your specific personal questions.

July 11, 2001 -- © 2001 DO health network