Low energy availability, not stress of exercise, alters LH pulsatility in exercising women

Abstract

We tested two hypotheses about the disruption of luteinizing hormone (LH) pulsatility in exercising women by assaying LH in blood samples drawn at 10-min intervals over 24 h from nine young, habitually sedentary, regularly menstruating women on days 8, 9, or 10 of two menstrual cycles after 4 days of intense exercise [E = 30 kcal.kg lean body mass (LBM)-1.day-1 at 70% of aerobic capacity]. To test the hypothesis that LH pulsatility is disrupted by low energy availability, we controlled the subjects' dietary energy intakes (I) to set their energy availabilities (A = I - E) at 45 and 10 kcal.kg LBM-1.day-1 during the two trials. To test the hypothesis that LH pulsatility is disrupted by the stress of exercise, we compared the resulting LH pulsatilities to those previously reported in women with similar controlled energy availability who had not exercised. In the exercising women, low energy availability reduced LH pulse frequency by 10% (P 0.4). During exercise, the proportion of energy derived from carbohydrate oxidation was reduced from 73% while A = 45 kcal.kg LBM-1.day-1 to 49% while A = 10 kcal.kg LBM-1.day-1 (P < 0.0001). These results contradict the hypothesis that LH pulsatility is disrupted by exercise stress and suggest that LH pulsatility in women depends on energy availability.