Abstract
INTRODUCTION: The release of luteinising hormone (LH) before ovulation is disrupted during a state of low energy availability (EA). However, it remains unknown whether a threshold EA exists in athletic populations to trigger ovulatory disturbances (anovulation and luteal phase deficiency) as indicated by peak/mid-luteal serum progesterone concentration (Pk-PRG) during the menstrual cycle. METHODS: We assessed EA and Pk-PRG in 15 menstrual cycles to investigate the relationship between EA and Pk-PRG in free-living, competitive (trained-elite) Guatemalan racewalkers (n = 8) and runners (n = 7) [aged: 20 (14-41) years; post-menarche: 5 (2-26) years; height: 1.53 ± 0.09 m; mass: 49 ± 6 kg (41 ± 5 kg fat-free mass "FFM")]. EA was estimated over 7 consecutive days within the follicular phase using food, training, and physical activity diaries. A fasted blood sample was collected during the Pk-PRG period, 6-8 days after the LH peak, but before the final 2 days of each cycle. Serum progesterone concentration was quantified using electrochemiluminescence immunoassay. RESULTS: Participants that reported an EA of <35 kcal·kg FFM(-1)·day(-1) (n = 7) exhibited ovulatory disturbances (Pk-PRG ≤9.40 ng·mL(-1)). Athletes with EA ≥36 kcal·kg FFM(-1)·day(-1) (n = 8) recorded "normal"/"potentially fertile" cycles (Pk-PRG >9.40 ng·mL(-1)), except for a single racewalker with the lowest reported protein intake (1.1 g·kg body mass(-1)·day(-1)). EA was positively associated with Pk-PRG [r(9) = 0.79, 95% confidence interval (CI): 0.37-0.94; p = 0.003; 1 - β = 0.99] after excluding participants (n = 4) that likely under-reported/reduced their dietary intake. CONCLUSIONS: The result from the linear regression analysis suggests that an EA ≥ 36 kcal·kg FFM(-1)·day(-1) is required to achieve "normal ovulation." The threshold EA associated with ovulatory disturbances in athletes and non-invasive means of monitoring the ovulatory status warrant further research.