Reproductive and metabolic adaptation to multi-stressor training in women

Hypothalamic-pituitary-gonadal (HPG) axis suppression in exercising women can be caused by low energy availability (EA) but the impact of a real-world, multi-stressor training environment on reproductive and metabolic function is unknown. This study aimed to characterize reproductive and metabolic adaptation in women undertaking basic military training. Design: Prospective cohort study in women undertaking 11-month initial military training (n=47). Dynamic low dose 1-hour GnRH tests were completed after 0 and 7 months of training. Urine progesterone was sampled weekly throughout. Body composition (dual x-ray absorptiometry), fasting insulin resistance (homeostatic modelling assessment 2, HOMA2), leptin, sex steroids, AMH and inhibin B were measured after 0, 7 and 11 months with an additional assessment of body composition at 3 months. Results: LH and FSH responses were suppressed after 7 months (both p<0.001). Among non-contraceptive users (n=20), 65% had regular (23–35d) cycles pre-enrolment, falling to 24% by 7 months of training. Of women in whom urine progesterone was measured (n=24), 87% of cycles showed no evidence of ovulation. There was little change in AMH, LH and estradiol, although inhibin B and FSH increased (p<0.05). Fat mass fluctuated during training but at month 11 was unchanged from baseline. Fat-free mass did not change. Visceral adiposity, HOMA2 and leptin increased (all p<0.001). Conclusions: HPG axis suppression with anovulation occurred in response to training without evidence of low EA. Increased insulin resistance may have contributed to the observed pituitary and ovarian dysfunction. Our findings are likely to represent an adaptive response of reproductive function to the multi-stressor nature of military training.