EFFECTS OF ARTERIAL PERFUSION-PRESSURE ON FORCE PRODUCTION IN WORKINGHUMAN HAND MUSCLES

1. The effects of hydrostatic changes in perfusion pressure on perform ance of working fatigue resistant muscle fibres in the hand were studi ed in six normal subjects. 2. Supramaximal stimuli were delivered in t rains of 200 ms duration, at 1 train s(-1), to the ulnar nerve proxima l to the wrist to produce isometric contractions of adductor pollicis. The force of contraction was measured and, after a level contraction force was achieved, the arm was passively raised or lowered. 3. Liftin g the hand 45 cm above the heart produced a decline in force output fr om the muscle within several seconds which, after 4 min, fell by 22% b elow the steady-state level. Lowering the hand 45 cm below heart level produced an 8% increase in force output. Greater changes in force out put occur at higher workloads. 4. It is concluded that in human subjec ts, muscle performance is sensitive to changes in perfusion pressure t hat occur across the physiological range. At moderate work levels, for ce output of the working muscles in the hand can vary by up to 30% ove r the physiological range of blood pressure. This dependence of muscul ar force on blood perfusion is of potential importance to motor contro l during normal activities.