Stress hormone responses to an ultraendurance race in the cold

Physical 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.

Forty-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. Pre-race weight and blood samples were collected 2 days prior to the race start. Post-race 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.

Runners lost significant weight (-1.74 kg +/- 1.29) pre-race to post-race. Hematocrit was maintained, and plasma volume increased minimally. Norepinephrine increased significantly pre-race (279.9 pg/mL +/- 356.9) to post-race (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 pre-race (12.03 microg/dL +/- 5.66) to post-race (26.69 microg/dL +/- 5.77), and post-race cortisol was significantly higher in runners vs skiers.

These 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.