The role of dehydroepiandrosterone levels on physiologic acclimatization to chronic mountaineering activity.

Previous studies have reported that glucose tolerance can be improved by short-term altitude living and activity. However, not all literature agrees that insulin sensitivity is increased at altitude. The present study investigated the effect of a 25-day mountaineering activity on glucose tolerance and its relation to serum levels of dehydroepiandrosterone-sulfate (DHEA-S) and tumor necrosis factor-alpha (TNF-alpha) in 12 male subjects. On day 3 at altitude, we found that serum DHEAS was reduced in the subjects with initially greater DHEA-S value, whereas the subjects with initially lower DHEA-S remained unchanged. To further elucidate the role of DHEA-S in acclimatization to mountaineering activity, all subjects were then divided into lower and upper halves according to their sea-level DHEA-S concentrations: low DHEA-S (n = 6) and high DHEA-S groups (n = 6). Glucose tolerance, insulin level, and the normal physiologic responses to altitude exposure, including hematocrit, hemoglobin, erythropoietin (EPO), and cortisol were measured. We found that glucose and insulin concentrations on an oral glucose tolerance test were significantly lowered by the mountaineering activity only in the high DHEA-S group. Similarly, hematocrit and hemoglobin concentration in altitude were increased only in the high DHEA-S group. In contrast, the low DHEA-S subjects exhibited an EPO value at sea level and altitude greater than the high DHEA-S group, suggesting an EPO resistance. The findings of the study imply that DHEA-S is essential for physiologic acclimatization to mountaineering challenge.

Validity of the 3 min step test in moderate altitude: environmental temperature as a confounder.

The 3 min step test is a widely used method to evaluate physical fitness, but whether this method is valid when performed at altitude is unknown. The purpose of this study was to examine the effect of altitude on the fitness score of the 3 min step test, and the role of ambient temperature in this effect. In study I, 11 healthy volunteers (aged 18.1 +/- 1.1 years) performed a 3 min step test at sea level and at altitude (1950 m). Plasma lactate and stress hormones, as indicators of metabolic stress, were measured before and after the test. To determine the role of ambient temperature, we performed study II at sea level with the same step test simulating the altitude temperature condition (24 degrees C at high altitude versus 32 degrees C at sea level) with 23 subjects (aged 20.4 +/- 0.4 y). In study I, plasma lactate of the subjects was elevated during the step test at sea level and to a greater extent at high altitude. Plasma cortisol and testosterone levels were elevated only at high altitude. However, the heart rate (HR) recovery after the step test was faster at high altitude than at sea level, producing a better physical fitness index. Furthermore, in study II, we demonstrated that the subjects who performed the 3 min step test at 24 degrees C exhibited faster HR recovery than at 32 degrees C. The current study therefore suggests that environmental conditions leading to temperature variation have strong confounding effects on the fitness score of the 3 min step test.