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

V'O2; fH, Q'; SV, [Hb], CaO2, Q'aO2, MAP and RP 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. fH 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'aO2 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 fH 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.