Stress Hormone Responses to an Ultraendurance Race in the Cold

ObjectivePhysical stress (exercise and/or environmental) activates the sympathetic-adrenal-medullary (SAM) and hypothalamic-pituitary-adrenocortical (HPA) axes. The combination of ultraendurance exercise in the cold presents a unique summated stress to the body. The purpose of this study was to assess the stress hormone response in runners, cyclists, and skiers participating in a 161-km ultraendurance race on a snow-packed course in the Alaskan wilderness.MethodsForty-four athletes (20 runners, 17 cyclists, 7 skiers) competed on the same course of snow-machine trails and ice roads with each athlete carrying 7 kg of mandatory equipment. Prerace weight and blood samples were collected 2 days prior to the race start. Postrace measurements were made within 15 minutes of race finish. Hematocrit was measured, and blood samples were analyzed for levels of norepinephrine, epinephrine, adrenocorticotropic hormone, and cortisol.ResultsRunners lost significant weight (−1.74 kg ± 1.29) prerace to postrace. Hematocrit was maintained, and plasma volume increased minimally. Norepinephrine increased significantly prerace (279.9 pg/mL ± 356.9) to postrace (691.7 pg/mL ± 422.6) with no difference among divisions. Epinephrine did not change significantly during the race. Adrenocorticotropic hormone (2.40 pg/mL ± 2.40 to 19.04 pg/mL ± 45.38) increased significantly with no difference among divisions. Cortisol increased significantly prerace (12.03 μg/dL ± 5.66) to postrace (26.69 μg/dL ± 5.77), and postrace cortisol was significantly higher in runners vs skiers.ConclusionsThese data suggest activation of both the SAM and HPA axes from an ultraendurance race in the cold and reveal the degree of stress hormone responses to this exhausting bout of exercise.