Cardiac output and cardiac load during isometric exercise in man

Cardiac output, heart rate, arterial pressure and indirect left ventricular oxygen consumption have been measured in three subjects during isometric contractions (50 - 170 kg) of the plantar flexors until fatigue was reached and during walking on a treadmill. Cardiac output was linearly related to V(O2) for both exercises. However, for the same V(O2) Q was four times higher during isometric effort than during walking. In the last 15 s of static tasks, HR was linearly increasing to V(O2) and AP reached values of 160 and 125 Torr (systolic and diastolic, respectively) independently of V(O2). For comparable V(O2) in static and isotonic exercises myocardial O2 uptake was doubled during isometric rather than during the isotonic exercise.