Frey, MAB, JT Lightfoot, ML Lasley, KL Mathes, CM Tomaselli, VA Convertino. Responses to lower body negative pressure in men of varying strength and aerobic fitness . Aviation, Space, and Environmental Medicine. 58: 483, 1987.
We investigated associations of leg strength (LS) and aerobic fitness (VO2max) with responses to lower-body negative pressure (LBNP). Four groups of six healthy men 25-39 yr were tested in graded LBNP, to -50mmHg or presyncope, after 90 min at 6¡ head-down tilt. Groups had a combination of either "high" or "low LS with "high" or "low" VO2max. Heart rate (HR), stroke volume, arterial pressures (AP), peripheral resistace (PR), calf circumference, thoracic fluid volume, plasma volume, norepinephrine (NE), epinephrine (E), vasopressin (VP), and plasma renin activity (PRA) were determined pre- and peak-LBNP. All groups exhibited typical hemodynamic responses to LBNP, with no group differences (ANOVA alpha=0.05). NE increased in all groups; VP did not change. E increased only in high LS groups; PRA only in high aerobic groups. Responses correlated (p<0.05) with change in mean ap were vp(-), hr(+), and pr(+). seven subjects became presyncopal: one low ls/ vo2max, two in each of the other groups (chi square="NS," p="0.895)." ls and vo2max were not correlated with fall in mean ap. neither ls nor vo2max is a determinant of tolerance to these levels of lbnp, nor do they affect responsiveness of hr and pr.