SYMPATHOADRENAL RESPONSES DURING EXERCISE AT HIGH ALTITUDE IN WOMEN

Abstract

1515 We have previously documented an enhanced sympathoadrenal response during exercise to high altitude in men. The purpose of this investigation was to determine 1) if women respond in a similar manner as found previously in men, and 2) the extent to which menstrual cycle phase influences this response. Sixteen eumenorrheic women (23.6±1.2 yrs, 56.2±4.3 kgs) were studied at sea level and after 10 days of high altitude exposure (4,300 m) either in their follicular (F, n=11) or luteal (L, n=5) phase. While at sea level, subjects performed two 45 minute submaximal steady-state exercise tests(on separate days) on a bicycle ergometer at intensities which elicited 50& 65% VO2max. During day 10 of altitude exposure, an absolute exercise intensity similar to that of 50% sea level VO2max was chosen such that subjects were working at the same absolute VO2 which represented 65% of their VO2max at altitude. Compared to rest, plasma epinephrine levels increased 36% in response to exercise at 50% VO2max at sea level with no differences found between cycle phase. This increase was significantly greater (↑44%) during exercise at 65% VO2max. At altitude, the epinephrine response was identical to that found for 65% VO2max exercise at sea level (↑44%) with no differences found between phase assignments. The plasma norepinephrine response was similar to that found for epinephrine such that the increase with exercise at altitude(↑51%) was the same as 65% VO2max exercise at sea level (↑50%). Again, no phase differences were observed. It was concluded that the sympathoadrenal response to exercise: 1) did not differ between cycle phase across any condition; 2) was similar to that found previously in men and; 3) the relative exercise intensity is the primary factor responsible for the catecholamine response to exercise.