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

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Abstract
Loucks, A. B., M. Verdun, and E. M. Heath. Low energy availability, not stress of exercise, alters LH pulsatility in exercising women. J. Appl. Physiol.84(1): 37–46, 1998.—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 ondays 8,9, or10 of two menstrual cycles after 4 days of intense exercise [E = 30 kcal ⋅ kg lean body mass (LBM)−1 ⋅ day−1at 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−1during 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 < 0.01) during the waking hours and increased LH pulse amplitude by 36% (P = 0.05) during waking and sleeping hours, but this reduction in LH pulse frequency was blunted by 60% (P = 0.03) compared with that in the previously studied nonexercising women whose low energy availability was caused by dietary restriction. The stress of exercise neither reduced LH pulse frequency nor increased LH pulse amplitude (allP > 0.4). During exercise, the proportion of energy derived from carbohydrate oxidation was reduced from 73% while A = 45 kcal ⋅ kg LBM−1 ⋅ day−1to 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.