Energy availability discriminates clinical menstrual status in exercising women.
BACKGROUND
Conditions of low energy availability (EA) (<30 kcal/kgLBM) have been associated with suppressed metabolic hormones and reductions in LH pulsatility in previously sedentary women during short-term manipulations of energy intake (EI) and exercise energy expenditure (EEE) in a controlled laboratory setting. The purpose of this study was to examine if EA, defined as EA = (EI-EEE)/kgLBM, is associated with disruptions in ovarian function in exercising women.


METHODS
Menstrual status was confirmed with daily measures of urinary reproductive metabolites across 1-3 menstrual cycles or 28-day monitoring periods. EA was calculated for exercise days using EI from 3-day diet logs, EEE from heart-rate monitors and/or exercise logs for a 7-day period, and body composition from DXA. Resting energy expenditure (REE) was measured by indirect calorimetry. Total triiodothyronine (TT3) was measured from a fasting blood sample.


RESULTS
91 exercising women (23.1 ± 0.5 years) were categorized clinically as either exercising amenorrheic (ExAmen, n = 30), exercising oligomenorrheic (ExOligo, n = 20) or exercising eumenorrheic (ExEumen, n = 41). The eumenorrheic group was further divided into more specific subclinical groups as either exercising ovulatory (ExOv, n = 20), exercising inconsistent (ExIncon, n = 13), or exercising anovulatory (ExAnov, n = 8). An EA threshold of 30 kcal/kgLBM did not distinguish subclinical menstrual status (χ (2) = 0.557, p = 0.46) nor did EA differ across subclinical disturbance groups (p > 0.05). EA was lower in the ExAmen vs. ExEumen (30.9 ± 2.4 vs. 36.9 ± 1.7 kcal/kgLBM, p = 0.04). The ratio of REE/predicted REE was lower in the ExAmen vs. ExEumen (0.85 ± 0.02 vs. 0.92 ± 0.01, p = 0.001) as was TT3 (79.6 ± 4.1 vs. 95.3 ± 2.9 ng/mL, p = 0.002).


CONCLUSIONS
EA did not differ among subclinical forms of menstrual disturbances in a large sample of exercising women, but EA did discriminate clinical menstrual status, i.e., amenorrhea from eumenorrhea.
Department of Kinesiology, Women's Health and Exercise Laboratory, 108 Noll Laboratory, The Pennsylvania State University, University Park, PA 16802 USA ; Current address: Division of Prevention and Rehabilitation, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, ON K1Y 4W7 Canada.
Jennifer L
JL
Reed
Department of Kinesiology, Women's Health and Exercise Laboratory, 108 Noll Laboratory, The Pennsylvania State University, University Park, PA 16802 USA.
Mary Jane
MJ
De Souza
Department of Kinesiology, Women's Health and Exercise Laboratory, 108 Noll Laboratory, The Pennsylvania State University, University Park, PA 16802 USA.
Rebecca J
RJ
Mallinson
Department of Kinesiology, Women's Health and Exercise Laboratory, 108 Noll Laboratory, The Pennsylvania State University, University Park, PA 16802 USA ; Current address: Department of Pediatrics, School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY USA.
Jennifer L
JL
Scheid
Department of Kinesiology, Women's Health and Exercise Laboratory, 108 Noll Laboratory, The Pennsylvania State University, University Park, PA 16802 USA.
Nancy I
NI
Williams
Dietary energy intake; Energy balance; Exercise training; Females; Resting metabolic rate; Total triiodothyronine