Relationship Between Energy Availability Changes And Endocrinological Markers In Male Long-distance Runners: A Longitudinal Study

Studies on relative energy deficiency in sport (REDs) in males are limited. Determining a threshold for low energy availability (LEA) in free-living athletes is challenging, and REDs symptoms may vary in males. It is essential to understand the response of endocrinological outcomes to energy availability (EA) changes, especially in endurance athletes with a high prevalence of LEA. PURPOSE: This study aimed to identify the relationship between the EA changes and endocrinological outcomes of REDs in male long-distance runners during the competitive season. METHODS: Twenty male long-distance runners (age; 20 ± 1 years) participated in measurements at the start of the competitive season (PRE) and after two months (POST). Blood samples were collected early morning in a fasting state, and free testosterone, cortisol, insulin-like growth factor I, and triiodothyronine were measured. Energy intake (EI) was assessed by 3-day dietary records with photographic intelligence. Exercise energy expenditure (EEE) measured on the same day as EI using a 3-axis accelerometer. Dual-energy X-ray absorptiometry was used to measure the fat-free mass (FFM). EA was calculated as EI minus EEE relative to FFM. The amount of change (Δ) was calculated by subtracting the PRE values from POST. RESULTS: EA in POST decreased significantly compared with that in PRE (PRE: 33.8 [29.7-43.3] kcal/kg FFM/day, POST: 30.7 [24.3-40.7] kcal/kg FFM/day, p = 0.006). EI decreased in POST, but EEE was not significantly different between PRE and POST. Excluding cortisol (PRE: 21.6 [20.0-22.5] μg/dL, POST: 17.9 [14.8-21.1] μg/dL, p < 0.001), there were no significant changes in blood markers between PRE and POST. However, Δ EA tended to be positively correlated with Δ free testosterone (r = 0.411, p = 0.072). CONCLUSIONS: EA decreased in male long-distance runners during the competitive season. Whether LEA exposure or not, EA changes were related to the change in testosterone value.