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

(VO2; fH, (Q), SV, [Hb], CaO2, (Q)(a)O-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, CaO2 decreased at rest (-8%) and at 50 W (-5%), whereas (Q)(a)O-2 did not change; MAP was 14 and 6% lower at rest and at 100 W and RP decreased by 23% only at rest. Changes in f(H) and SV were larger after HDTBR than after AMB. These results show that, notwhistanding the drop of SV, moderate-intensity dynamic exercise elicited a normal pressure response after 14 days of HDTBR.