Characteristics Of The Primary Indicators Of Relative Energy Deficiency In Sport (REDs) In Male Athletes

The International Olympic Committee (IOC) Relative Energy Deficiency in Sport (REDs) Clinical Assessment Tool: Version 2 (IOC REDs CAT2) was introduced in 2023. The IOC REDs CAT2 is innovative and more accessible because it does not rely on the calculation of energy availability. Previous studies have reported that low energy availability, which results from restricted energy intake and increased exercise energy expenditure in laboratory settings, alters physiological responses. However, the physiological response in athletes under free-living conditions appear to be complex, particularly in men. PURPOSE: To identify the characteristics of primary indicators of REDs in free-living male athletes. METHODS: Forty collegiate athletes, including 20 American football players (height,172.4 ± 5.3 cm; weight, 86.6 ± 11.8 kg; age, 20 ± 1 years) and 20 long-distance runners (height, 170.3 ± 5.4 cm; weight, 56.9 ± 4.7 kg; age, 20 ± 1 years) participated. Fasting blood samples collected early in the morning were analyzed for free testosterone (free-T) and triiodothyronine (T3) levels. Dual-energy X-ray absorptiometry was used to measure lumbar spine bone mineral density Z-scores. The history of bone stress injuries within the past two years was collected through a questionnaire. Free-T and T3 level were compared between the athletic disciplines. In addition, the relationship between athletic discipline and the number of participants who met the primary indicators of REDs was investigated. RESULTS: Long-distance runners had a significantly lower free-T levels (12.9 ± 3.2 pg/mL vs. 18.8 ± 4.5 pg/mL, p < .001) and a significantly lower T3 levels (104.1 ± 16.6 ng/dL vs. 118.3 ± 18.9 ng/dL, p = .016) compared to American football players. A chi-square test of independence revealed a significant association between athletic discipline and the number of participants who met the primary indicators of REDs (X2 = 13.69 [df = 3, N = 40], p = .003). CONCLUSIONS: In long-distance runners, the levels of free-T and T3, which are the primary indicators of REDs, were low. Additionally, athletic discipline was related to the number of participants who met the primary indicators of REDs. These findings suggest that male long-distance runners may be at potential risk for REDs. Supported by: Waseda University Grant for Special Research Projects (Project number: 2024C-587).