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

\( {{\dot{V}O}}_{2} , \) f _H, \( \dot{Q}, \) SV, [Hb], C_aO₂, \( {{\dot{Q}}}_{\text{a}} \)O₂, 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 \( \dot{Q} \) did not change. After HDTBR, C_aO₂ decreased at rest (−8%) and at 50 W (−5%), whereas \( {{\dot{Q}}}_{\text{a}} \)O₂ 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, notwhistanding the drop of SV, moderate-intensity dynamic exercise elicited a normal pressure response after 14 days of HDTBR.