Sensitivity and Specificity of an Energy Availability Threshold in Differentiating Menstrual Status in Exercising Premenopausal Women

Abstract

Luteinizing hormone (LH) pulsatility is disrupted in regularly menstruating women below an energy availability (EA) threshold of 30 kcal/kg FFM when EA is calculated as (intake-exercise kcals)/kg FFM as indicated by experiments in previously sedentary women studied for 5 d under lab exercise conditions. PURPOSE To examine the sensitivity (SE) and specificity (SP) of an EA threshold of 30 kcal/kg FFM in differentiating menstrual status in exercising premenopausal women as well as factors contributing to reduced SE and or SP. METHODS Blood samples for endocrine and metabolic hormones, a physical exam, self reported menstrual histories and measurements of urinary estrone-1-glucuronide, pregnanediol-3-glucuronide and LH across 1 menstrual cycle confirmed exercise associated functional hypothalamic amenorrhea (FHA) or ovulatory (OV) menstrual status. EA was calculated for 7 d. Body composition using DXA, energy intake (EI) using 3 d diet logs, exercise energy expenditure (EEE) from heart rate monitors and eating behaviors were examined. An EA threshold to differentiate menstrual status was examined by calculating SE ((FHA below threshold/all FHA)*100) and SP ((OV above threshold/all OV)*100). RESULTS OV (n=32) and FHA (n=22) were of similar (p>0.05) age (23.1±0.6 yrs), weight (57.6±0.8 kg), height (165.5±0.9 cm) and VO2max (48.1±1.2 ml/kg/min). FHA had a higher age of menarche (13.8±0.4 vs 12.4±0.2 yrs; p=0.001), lower fat mass (12.5±0.7 vs 15.3±0.5 kg; p=0.002) and lower body fat % (22.3±0.9 vs 26.1±0.7 %; p=0.002) compared to OV. The SE and SP of the EA threshold were 45.5% and 78.1%, respectively. In examining factors contributing to reduced SE, FHA above the threshold had increased EI (2016±74 vs 1431±206 kcal/d; p=0.010) and decreased EEE (239±44 vs 513±83 kcal/d; p=0.006) compared to FHA below the threshold resulting in higher EA; they did not differ from FHA below the threshold in terms of chronic indicators of energy deficiency (ED) i.e. FFM (p=0.415), BMI (p=0.207) or BF% (p=0.238). CONCLUSION An EA threshold of 30 kcal/kg FFM provides high SP, not SE, in differentiating menstrual status in exercising premenopausal women. Low SE may be a result of EA being an acute, not chronic, indicator of ED in FHA. FHA in exercising women may also be associated with other contributing factors. DOD W8IXWH0610145 NATA 206GGP008