Serum testosterone concentration during two hours of moderate intensity treadmill running in trained men and women.

The purpose of this study was to determine alterations in testosterone concentration in women during 2 hours of moderate intensity running, and to compare this response to that seen in men. Maximal oxygen uptake (VO2 max) and anaerobic threshold (AT) were determined in 11 men and 9 women. These subjects subsequently ran for 2 hours on a motor-driven treadmill at 10% below the AT which was approximately 70% VO2 max. Blood samples were drawn at 0, 30, 60, 90 and 120 minutes of exercise and testosterone was measured by specific radioimmunoassay. Serum testosterone concentration was significantly increased (41%, P less than .01) after 30 minutes of exercise in the men. In the women, testosterone was not significantly increased from pre-exercise concentrations until 120 minutes of exercise (48%, P less than .01). At this time the testosterone concentration in the men had decreased and was no longer significantly elevated from the pre-exercise concentration. The magnitude of the increases in serum testosterone concentration can probably be accounted for by decreases in the metabolic clearance rate of sex-steroids known to occur during exercise. Differences in the testosterone response between men and women during prolonged aerobic exercise are of interest and may imply that different mechanisms of control are involved.