Central command increases cardiac output during static exercise in humans

Neural control of the circulation during static two-leg exercise was evaluated in 10 subjects. External compression of the legs was employed to assess muscle mechano-receptor influence by achieving the same intramuscular pressure (80 mmHg) as developed during exercise. The muscle metabo-reflex contribution was assessed by post-exercise muscle ischaemia, and the influence from higher centres in the central nervous system ('central command') was taken as the part of the response that could not be accounted for by the two reflex contributions. During static exercise, mean arterial pressure was higher (26 +/- 3 mmHg; P < 0.01) as compared with leg compression (10 +/- 2 mmHg) and with post-exercise muscle ischaemia (11 +/- 2 mmHg). Heart rate (25 +/- 4 b.p.m.) and cardiac output (0.8 +/- 0.3 L min-1) were increased only during static exercise (P < 0.05). Increase in total peripheral resistance were similar during static exercise, post-exercise muscle ischaemia and leg compression. The pressor response to static exercise with a large muscle group was equally attributable to mechanical and metabolic stimulation of afferent nerves; and the two influences were redundant in their effect on total peripheral resistance. In contrast, the influence from central command was directed to the heart with elevation of its rate and minute volume.