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This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 99/5/1930    most recent 00565.2005v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Braun, B. Articles by Chipkin, S. R. Search for Related Content PubMed PubMed Citation Articles by Braun, B. Articles by Chipkin, S. R.

No effect of short-term testosterone manipulation on exercise substrate metabolism in men

¹Department of Exercise Science, University of Massachusetts, Amherst; and ²Department of Obstetrics and Gynecology, Baystate Medical Center, Springfield, Massachusetts

Submitted 13 May 2005 ; accepted in final form 29 June 2005

Compared with women, men use proportionately more carbohydrate and less fat during exercise at the same relative intensity. Estrogen and progesterone have potent effects on substrate use during exercise in women, but the role of testosterone (T) in mediating substrate use is unknown. The purpose of this investigation was to assess how large variations in the concentration of blood T would impact substrate use during exercise in men. Nine healthy, active men were studied in three distinct hormonal conditions: physiological T (no intervention), low T (pharmacological suppression of endogenous T with a gonadotrophin-releasing hormone antagonist), and high T (supplementation with transdermal T). Total carbohydrate oxidation, blood glucose rate of disappearance, and estimated muscle glycogen use were assessed by using stable isotope dilution and indirect calorimetry at rest and while bicycling at 60% of peak O₂ consumption for 90 min. Relative to the physiological condition (T = 5.5 ± 0.5 ng/ml), total plasma T was considerably suppressed in low T (0.8 ± 0.1) and elevated in high T (10.9 ± 1.1). Despite the large changes in plasma T, carbohydrate oxidation, glucose rate of disappearance, and estimated muscle glycogen use were very similar across the three conditions. There were also no differences in plasma concentrations of glucose, insulin, lactate, or free fatty acids. Plasma estradiol (E) concentrations were elevated in high T, but correlations between substrate use and plasma concentrations of T, E, or the T-to-E ratio were very weak (r² < 0.20). In conclusion, unlike the effect of acute elevation in E to constrain carbohydrate use in women, acute changes in circulating T concentrations do not appear to alter substrate use during exercise in men.

androgen; carbohydrate oxidation; fat oxidation; glucose uptake; stable isotope; glycogen