Abstract

Background: Severe physical and environmental stress appears to have a suppressive effect on the hypothalamic-pituitary gonadal (HPG) axis in men. Examining hormonal responses to an actual extreme 160 km competition across frozen Alaska provides a unique opportunity to study this intense stress.

Objective: To examine hormonal responses to an ultra-endurance race. Methods: Blood samples were obtained from 16 men before and after racing, and analyzed for testosterone, interleukin-6 (IL-6), growth hormone (GH), and cortisol. Six subjects (age, (Mean ± SD) 42 ± 7 y; body mass, 78.9 ± 7.1 kg; height , 1.78 ± 0.05 m) raced by bicycle (cyclists) and ten subjects (age, 35 ± 9 y; body mass 77.9 ± 10.6 kg; height, 1.82 ± 0.05 m) raced by foot (runners); mean (± SD) finish times were 21.83 ± 6.27 hr and 33.98 ± 6.12 hr, respectively.

Results: In cyclists there were significant (p ≤ 0.05) pre- to post-race increases in cortisol (mean ± SD, 254.83 ± 135.26 to 535.99 ± 232.22 nmol•L-1), GH (0.12 ± 0.23 to 3.21 ± 3.33 µg•ml-1), and IL-6 (2.36 ± 0.42 to 10.15 ± 0.3.28 pg•ml-1), and a significant decrease in testosterone (13.81 ± 3.19 to 5.59 ± 3.74 nmol•L-1). Similarly, in runners there were significant pre- to post-race increases in cortisol (142.09 ± 50.74 to 452.21 ± 163.40 ng•ml-1), GH (0.12 ± 0.23 to 3.21 ± 3.33 µg•ml-1), IL-6 (2.42 ± 0.68 to 12.25 ± 1.78 pg•ml-1), and a significant decrease in testosterone (12.32 ± 4.47 to 6.96 ± 3.19 nmol•L-1). There were no significant differences in the hormonal concentrations between the cyclists and runners (p > 0.05).

Conclusions: These data suggest a suppression of the hypopituitary-gonadal-axis potentially mediated by amplification of adrenal stress responses to such an ultra-endurance race in environmentally stressful conditions.