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Abstract
To assess plasma progesterone (P) response to progressive exercise, 17 female recreational runners participated in a study spanning 7 menstrual cycles. Control subjects (C) (n=8) maintained their usual physical activity at baseline levels (14-19 mi/week), while experimental subjects (E) increased their average mileage from 20 to 32 mi/week. Blood samples drawn every other day during the 1st and 7th menstrual cycles, beginning on Day 10 of each cycle, were analyzed for luteinizing hormone and P. Activity and diet records for Days 3-10 of the 1st, 3rd, 5th, and 7th menstrual cycle provided estimates of energy balance. Coinciding with these records were 24-hr urine samples, which were analyzed for 3methylhistidine (3-MH). Subjects consumed a lacto-ovo vegetarian diet required for measurement of 3-MH. Among E subjects, the median number of days in which P concentration was greater than 6.0 ng/ml declined from 5.0 days at the 1st menstrual cycle to 0.0 days by the 7th cycle (p< .05). A significant decrease in the P-vs-time area under the curve was observed among C subjects (JD< .05). There were no statistically significant differences between C and E with respect to the degree of change in P concentrations, suggesting that the progressive exercise of the E subjects was not responsible for alterations in P.