Physiological adjustments of women to prolonged work during acute hypoxia

Five women (23-32 yr) performed bicycle work in a hypobaric chamber for 2 h at 41% of their respective altitude maximal oxygen uptakes (VO2) at 758, 586, 523, and 446 Torr barometric pressures (PB). Steady-state VO2 was achieved within 5 min work at all altitudes. Pulmonary ventilation (29.2 +/- 1.9 (mean +/- SE) 1/min, BTPS), respiratory rate (22 +/- 2 breaths/min), cardiac output (8.5 +/- 1.4 1/min), heart rate (115 +/- 6 beats/min), and stroke volume (75 +/- 13 ml) were similar at all altitudes, but time-related changes differed with altitude. Blood lactates did not change with work duration and were similar at 758 and 586 Torr PB but progressively elevated at 523 and 446 Torr. Blood norepinephrine, measured only at 758 and 446 Torr PB, increased with work but not altitude; epinephrine increased only at altitude. Norepinephrine levels and respiratory, cardiovascular, and thermoregulatory functions were essentially dependent on relative work load; blood lactates and epinephrine levels were not. Many physiological functions in these women performing sustained light work during acute altitude exposure were remarkably stable in contrast to previously reported studies on men.

Maximal work capacity of women during acute hypoxia

Six healthy women (22--34 yr of age) performed maximal bicycle work in a hypobaric chamber at sea level and at simulated altitudes of 2,130 and 3,050 m (barometric pressures, 758, 586, and 523 Torr). Maximal oxygen uptake (VO2max) decreased 10 and 15% from sea-level values at 2,130 and 3,050 m, respectively. At these altitudes minute ventilation (VEBTPS) increased 17 and 22% respectively, a consequence of increased respiratory rate (fR). Respiratory exchange ratios increased 10 and 14%, and oxygen pulse decreased 9 and 12%, respectively, at 2,130 and 3,050 m. Maximal blood lactates, heart rates, cardiac outputs, and plasma volume shifts were unaffected by these altitudes. Although during maximal work the percentage increases in VEBTPS, fR, and R that resulted from altitude exposure were greater in women than those previously reported for men, the decrements in VO2max were comparable to those in men. The results show that relative to their performance at sea level, men and women have equal ability to perform maximal work at altitudes up to 3,050 m.

Maximal oxygen uptake during exercise with various combinations of arm and leg work

Oxygen uptake (VO2) was determined in 10 males during the following types of maximal exercise (work time: about 5 min): uphill running, bicycling, arm work (cranking), and combined arm work and bicycling (A + L). The A + L exercise was performed in four different ways, the arms doing 10%, 20%, 30%, or 40% of the same total rate of work; and also with the maximal bicycle work load plus either maximal or submaximal arm work. VO2 was the same in running as in all types of A + L exercise, except when the arm work load was 10% and 40% of the total rate of work, where VO2 was 2.5% (P less than 0.05) and 9.4% (P less than 0.001) lower, respectively. Bicycle VO2 was lower than VO2 in running but equal to A + L VO2 when arm work intensity was 40% of the total rate of work. It is concluded that VO2 during maximal exercise a) to a certain extent depends on the exercising muscle mass, b) is lower than the oxygen-consuming potential of the muscles involved in A + L exercise, and c) in A + L exercise is influenced by the ratio of arm work to total rate of work and the subject's fitness for arm work and bicycling.