HUDSON, D. L., M. L. SMITH, and P. B. RAVEN. Physical fitness and hemodynamic response of women to lower body negative pressure. Med. Sci. Sports Exerc., Vol. 19, No. 4, pp. 375-381, 1987. Aerobic fitness as assessed by maximal aerobic capacity (V˙O2max) has been shown to be associated with an attenuated baroreflex function during lower body negative pressure (LBNP) in men. Sixteen women (mean age = 24.7 yrs) were evaluated during progressive LBNP to -50 torr. Each subject's V˙O2maxwas determined using indirect calorimetry during the Bruce protocol exercise test. Eight subjects [mean V˙O2max= 56.8 (ml O2· min-1) · kg-1] were designated as trained, and eight subjects [mean V˙O2max, = 39.4 (ml O2· min-1) · kg-1] were designated as untrained. During LBNP, heart rate, blood pressure, cardiac index, forearm blood flow, and leg circumference were measured. All subjects completed the LBNP protocol without clinical symptoms of pre-syncopy. The over-all hemodynamic responses of both groups to LBNP were qualitatively similar to previous findings reported for males. However, no significant differences in response of hemodynamic variables were observed between trained and untrained subjects during LBNP to -50 torr (P > 0.05) except for vascular resistance and diastolic blood pressure at -50 torr where the untrained value was greater than the trained value. This would suggest that a fitness-related difference may have been present at higher levels of LBNP. Furthermore, in contrast to previous reports in males, the index of baroreflex responsiveness (Δheart rate/Δsystolic blood pressure) was similar for both groups (P > 0.05). When these data were compared with a similar subject pool of males, the females displayed a significantly greater (P < 0.05) tolerance of LBNP to -50 torr regardless of fitness. It was apparent that this greater tolerance was associated with a greater regional vasoconstrictive response and a more responsive integrated baroreflex.
- Endurance training
- Orthostatic tolerance