Somatotrophic Hormonal Responses after U.S. Army Ranger Training and Relationship to Changes in Body Composition: 1402

Soldiers are periodically exposed to multi-stressor environments with subsequent alterations in anabolic/catabolic hormones. While these hormonal changes coincide with decrements in physical performance and alterations in body composition, their association is uncertain. PURPOSE: To examine somatotrophic hormonal changes after US Army Ranger training (ART) and their relationship to changes in body composition. METHODS: Fifty male Soldiers (25.6 ± 4.1 y, 176.5 ± 8.3 cm) completed the 8-wk ART course. This multi-stressor course consisted of deliberate energy restriction (∼1,350–1,570 kcal/d), high energy expenditure (∼3,200 kcal/d), limited/disrupted sleep (∼4 h/d), psychological and environmental stress. Testosterone (T), IGF-I, cortisol and DEXA-assessed body composition were measured before and after ART. Data were analyzed with paired t-test and presented as mean ± SD with p ≤ 0.05. RESULTS: Testosterone significantly decreased by ∼82 %, following ART, approaching hypogonadal concentrations (Pre: 17.3 ± 4.8; Post: 3.0 ± 1.8 nmol/L). Similarly, IGF-I was 57 % lower (Pre: 238.4 ± 80.6; Post: 108 ± 29.2 ng/mL) whereas cortisol was significantly increased by 32% (Pre: 469.3 ± 106.9; Post: 692.5 ± 109.3 nmol/L) following ART. After ART, losses of body mass (Pre: 81.5 ± 13.2 kg; Post: 65.1 ± 10.6 kg), fat-free mass (FFM: Pre: 66.5 ± 6.5; Post: 62.6 ± 5.9 kg) and fat mass (Pre: 11.7 ± 3.9; Post: 5.8 ± 2.2 kg) occurred following ART. Furthermore, changes in FFM were significantly correlated with changes in IGF-I (r = 0.42) and cortisol (r = −0.33), but not correlated with T (r = 0.22). Changes in fat mass were significantly correlated with changes in IGF-I (r = −0.30) and cortisol (r = 0.40), but not T (r = −0.20). CONCLUSION: The U.S. ART course produced robust physiological changes as evident by the dramatic alterations of circulating anabolic (testosterone and IGF-I), catabolic hormones (cortisol) and body composition. The association between changes in somatotrophic hormones and body composition (IGF-I explained 17 % of the variance, whereas cortisol explained 11% of the variance, with changes in FFM) may suggest that nutritional/pharmacological manipulation of circulating anabolic/catabolic hormones may be beneficial for preservation of fat-free mass during periods of physiological strain.