Adrenal Stress and Physical Performance During Military Survival Training

INTRODUCTION: The purpose of this research was to evaluate neuroendocrine and physical performance responses in sailors and Marines undergoing U. S. Navy Survival, Evasion, Resistance, and Escape (SERE) training. METHODS: Participants were 20 men (Age: 25.3 +/- 3.6 yr; Height: 178.1 +/- 6.1 cm; Weight: 83.7 +/- 12.6 kg). Men were further split into high fit (N = 10) and low fit (N = 10) subgroups based on physical fitness test scores. Blood samples were obtained at baseline (T1), stress (T2), and recovery (T3) timepoints, and were analyzed for plasma epinephrine, plasma norepinephrine, plasma dopamine, serum cortisol, serum testosterone, and plasma neuropeptide Y. Vertical jump and handgrip tests were performed at T1 and T2. RESULTS: Stress hormone concentrations were significantly elevated at T2, with a concomitant reduction in testosterone concentrations. NPY concentrations did not increase at T2, but decreased significantly at T3. Subjects maintained performance on vertical jump and handgrip tests from T1 to T2. Significant between group differences were observed in norepinephrine (high fit: 3530.64 +/- 2146.54 pmol.L-1, low fit: 4907.16 +/- 3020.85 pmol.L-1) and NPY (high fit: 169.30 +/- 85.89 pg.ml(-1), low fit: 123.02 +/- 88.86 pg.ml(-1)) concentrations at T3. CONCLUSION: This study revealed that despite significant increases in stress hormone concentrations in all subjects during SERE, fitter subjects exhibited differential hormonal responses during recovery, with quicker return of norepinephrine and NPY to baseline concentrations. This suggests physical fitness level may have a protective effect in recovery from periods of high stress military training.