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Peak athletic performance may be related to time of day, suggests a University of Chicago study being presented to the Endocrine Society’s annual meeting, ENDO 2001, in Denver, Colorado, on June 22, 2001. The study shows that the response of the systems regulating energy metabolism and some hormones differs according to when in the day exercise is performed.

Subjects who exercised at night had much larger drops in glucose levels in response to exercise than at other times of day. Exercise in the evening and at night elicited large increases in the levels of two hormones important for energy metabolism, cortisol and thyrotropin. Exercise at other times of day had much smaller effects on these hormones. In contrast, marked increases in growth hormone levels in response to exercise were not effected by the time of day.

“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 1-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.”

For the study, conducted in the Clinical Research Center of the University of Chicago, 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.”

When not exercising, the subjects rested in bed with constant glucose infusion to avoid fluctuation in their blood sugar levels caused by intermittent meals. Blood levels of the “circadian hormones,” melatonin, cortisol and thyrotropin, and the levels of growth hormone and glucose were compared to blood levels for the same time of day in the resting control subjects.

The importance of timing for hormonal secretion and energy metabolism is demonstrated by the distinct 24-hour patterns of secretion for each hormonal system. One hormone may be actively secreted in a complex pulsating pattern while another may be in a resting phase.

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. Although these metabolic and hormonal responses to morning exercise are well-documented, few studies have examined the effects of exercise at other times of day.

“Our study covers new ground, demonstrating variation in the effects of exercise at four different times of day, with circadian time precisely quantified, with a practical duration of exercise, and with a high intensity designed to elicit maximal effects” said Buxton.

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Jeanne Galatzer-Levy
University of Chicago Medical Center

Co-authors on the study include, André J. Scheen, M.D., Division of Diabetes, Nutrition and Metabolic Disorders, University of Liége, Belgium; Mireille L’Hermite-Balériaux, Ph.D., Laboratory of Experimental Medicine, Université Libre de Bruxelles, Belgium and Eve Van Cauter, Ph.D., Department of Medicine, University of Chicago.

This work was supported by grants from the Air Force Office of Scientific Research and from the Department of Defense. The University of Chicago Clinical Research Center is supported by a National Institutes of Health grant.

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Active individuals lacking in B-vitamins – including college athletes and other elite competitors — may perform worse during high-intensity exercise and have a decreased ability to repair and build muscle than counterparts with nutrient-rich diets, according to recent Oregon State University research published in the International Journal of Sport Nutrition and Exercise Metabolism.The B-vitamins include thiamin, riboflavin, vitamin B-6, B-12 and folate. These micronutrients are necessary during the body’s process for converting proteins and sugars into energy, and are used during the production and repair of cells, including red blood cells.

For active individuals a marginal deficiency in the nutrients may impact the body’s ability to repair itself, operate efficiently and fight disease, said Melinda Manore, researcher in the Colleges of Agricultural and Health and Human Sciences. Manore analyzed the athletic performance of several elite and collegiate athletes in her research, as well as less competitive individuals.

The stress on the body’s energy producing pathways during exercise, the changes in the body’s tissues resulting from training, an increase in the loss of nutrients in sweat, urine and feces during and after strenuous activity and the additional nutrients needed to repair and maintain higher levels of lean tissue mass present in some athletes and individuals may all affect an individuals B-vitamin requirements, said Manore.

“Many athletes, especially young athletes involved in highly competitive sports, do not realize the impact their diets have on their performance,” said Manore, who is also an Extension Service nutrition scientist. “By the time they reach adulthood they can have seriously jeopardized their abilities and their long-term health.”

Current national B-vitamin recommendations for active individuals may be inadequate, and athletes who follow the recommended daily allowances set by the U.S. government may be receiving lower amounts of nutrients than there bodies need, said Manore. Athletes who restrict calories or limit food groups like dairy or meat have an increased chance of deficiency. Such athletes are often concerned about maintaining a low body weight for sports like gymnastics and wrestling.

“The most vulnerable people are often the individuals society expects to be the healthiest,” said Manore. “There’s a lot of pressure on women in particular to look like an ‘athlete.’ Unfortunately for some people that means skinny and petite, rather than healthy and strong.”

The B-vitamins are in whole and enriched grains, dark green vegetables, nuts, and many animal and dairy products. Manore suggests athletes and individuals with poor or restricted diets consider taking a multivitamin or mineral supplement.

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Article adapted by MD Only Sports Weblog from original press release.
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Contact: Melinda Manore
Oregon State University