Metabolic and cardiovascular responses during sub-maximal exercise in humans after 14 days of head-down tilt bed rest and inactivity.

VO(2), f (H), Q, SV, [Hb], C(a)O(2), QaO(2), MAP and R (P) were measured in 10 young subjects at rest and during exercise at 50, 100 and 150 W before and after 14 days of head-down tilt bed rest (HDTBR) and of ambulatory (AMB) control period. f (H) was 18 and 8% higher after HDTBR and AMB, respectively. SV dropped by 15% both after HDTBR and AMB, whereas Q did not change. After HDTBR, C(a)O(2) decreased at rest (-8%) and at 50 W (-5%), whereas QaO(2) did not change; MAP was 14 and 6% lower at rest and at 100 W and R (P) decreased by 23% only at rest. Changes in f (H) and SV were larger after HDTBR than after AMB. These results show that, notwithstanding the drop of SV, moderate-intensity dynamic exercise elicited a normal pressure response after 14 days of HDTBR.