Longitudinal changes in psychological, physiological, and nutritional measures and predictors of success in Special Forces training.

The mentally and physically challenging 19-20 day, multi-stressor US Army Special Forces Assessment and Selection (SFAS) course selects soldiers for Army Special Forces (SF) training. If selected, candidates enroll for advanced training in the 2-year Special Forces Qualification Course (SFQC) to qualify for the SF. This longitudinal study examined physiological, psychological, and nutritional status of soldiers before (pre-SFAS) and after SFAS (post-SFAS), and post-SFQC, to identify predictors of graduation from SFQC. Fasting blood was collected from candidates (n =192) and assayed for physiological and nutritional biomarkers at all three times. Body composition and diet quality were assessed using skin folds and food-frequency questionnaires at all three times. Self-reported psychological measures at those times included resilience and Grit. Physical performance was assessed by SFAS staff. Changes over time and predictors of SFQC graduation were assessed with linear mixed models and logistic regression. The three weeks of SFAS reduced fat mass and fat-free mass, and increased HPA-axis, inflammatory, and appetite markers. Post-SFQC neuropeptide-Y concentrations, fat mass, fat-free mass, diet quality, and resilience fell below pre-SFAS values. Testosterone, DHEA-S, brain-derived neurotropic factor, IL-6 and prolactin were elevated after SFQC. Odds of graduating SFQC increased when cortisol increased during SFAS. Reduced body mass, fat mass, and BMI at SFAS and higher physical performance during SFAS also increased odds of graduating SFQC. This study documented changes occurring over approximately 2-years of SF training. In addition, it identified physical performance, body composition, and biochemical predictors of success at U.S. Army Special Forces training.