HORMONAL RESPONSES TO A 160KM RACE (SUSITNA 100) ACROSS FROZEN ALASKA.

Abstract

The year 2000 Susitna 100, formally named the Iditasport 100, provided a novel race in which to examine hormonal responses. The 160km race included an elevation gain of 2270m, the ambient temperature at the start of the race was 28oF and dropped to 20oF, accompanied by a wet snowfall, a few hours after starting. Furthermore it was mandatory that all racers carried survival gear weighing a minimum of 15lbs. PURPOSE To examine hormonal responses to a 160km race across frozen Alaska. METHOD Blood samples were obtained from sixteen men before and after racing, and analyzed for testosterone, interlukin-6 (IL-6), growth hormone(GH), and cortisol. Six of the subjects raced by bicycle and ten subjects raced by foot(runners); mean(±SD) finish times were 1310 ±376min and 2039 ±367min, respectively. RESULTS No differences were observed in the hormonal responses between the cyclists and runners. In the cyclists there was significant(p < .05) pre-to post-race increase in cortisol (mean ±SE, 138.89 ±14.86 to 440.64 ±48.15nmol/L), GH (0.12 ±0.00 to 3.22 ±1.05ng/ml), IL-6 (2.42 ±.25 to 12.25 ±0.56pg/ml), and a significant decrease in testosterone (12.32 ±1.41 to 6.96 ±1.00nmol/L). In the runners there was a significant pre- to post-race increase in cortisol (245.83 ±55.21 to535.98 ±94.80ng/ml), GH (0.1832 ±.00 to 3.73 ±0.53n/ml), IL-6 (2.42 ±0.21 to 12.25 ±0.56 pg/ml), and a significant decrease in testosterone (13.81 ±1.30 to 5.59 ±1.53nmol/L). CONCLUSION These data indicate a suppression of the hypopituitary gonadal axis potentially mediate by amplification of adrenal stress responses to such an ultra-endurance race.