Low energy availability, not stress of exercise, alters LH pulsatility in exercising women.
Level 3 - non-randomized controlled study
Controlled experimental crossover trial with historical comparison group
PubMed 9451615 · doi:10.1152/jappl.1998.84.1.37
What was done
Assayed luteinizing hormone (LH) in blood samples collected every 10 minutes over 24 hours in 9 young, habitually sedentary, regularly menstruating women on days 8, 9, or 10 of two menstrual cycles. Each cycle followed 4 days of intense exercise (30 kcal/kg lean body mass [LBM]/day at 70% aerobic capacity) with dietary intake controlled to produce energy availability levels of either 45 or 10 kcal/kg LBM/day. LH pulsatilities were compared between energy availability conditions and against previously published data from nonexercising women with matched energy availability to isolate the effect of exercise stress.
What was found
In exercising women, low energy availability (10 kcal/kg LBM/day) reduced waking LH pulse frequency by 10% (P < 0.01) and increased LH pulse amplitude across waking and sleeping hours by 36% (P = 0.05). The reduction in LH pulse frequency was blunted by 60% (P = 0.03) compared with previously studied nonexercising women under dietary restriction. Exercise stress did not reduce LH pulse frequency or increase pulse amplitude (all P > 0.4). Exercise carbohydrate oxidation dropped from 73% at 45 kcal/kg LBM/day to 49% at 10 kcal/kg LBM/day (P < 0.0001).
Why it matters
This study shows that exercise-associated reproductive neuroendocrine disruption is driven by low energy availability rather than the physiological stress of exercise itself, clarifying the etiology of athletic amenorrhea and the female athlete triad.
Limits
Small sample size (n = 9) restricted to young, habitually sedentary women over short 4-day interventions, which may not capture chronic adaptations in trained athletes. Comparisons assessing the specific effect of exercise stress relied on historical control data rather than a concurrent randomized non-exercising control group.
Cited by
- supports Women who are in a caloric deficit while performing extreme endurance or high-volume high-intensity exercise experience significant disruptions in reproductive hormones.