Response of arterial blood pressure to static exercise in relation to muscle mass, force development, and electromyographic activity.

In young men, the arterial blood pressure response during static exercise at 40% of maximal voluntary contraction (MVC) and the response after the contraction with a cuff inflated both were increased when a greater mass of skeletal muscle was involved. Also in men with a previously injured leg, the arterial systolic pressure and the smoothed, rectified electromyographic activity (EMG) were greater during static contraction of the large, strong leg than during static contraction of the small, weak leg at the same percent MVC. However, the arterial systolic pressure and the EMG were almost the same during contraction of either leg when the same force was developed. Finally, in young men, either the force developed was held constant at 20% MVC or the level of the initial EMG at 20% MVC was held constant for 5 minutes. During the force-constant experiments, the EMG doubled and correlated with the 40% increase in mean arterial pressure (r = 0.89). In the EMG-constant experiments, force declined to about 12% MVC with an increase of only 20% in mean arterial pressure. These studies of the response of arterial blood pressure to static muscular contractions can best be explained by both central and peripheral control mechanisms. The central control mechanism "central command" is probably related to the central activity for recruitment of motor units and the peripheral control mechanism is probably mediated by muscle afferents which are excited by metabolic changes in the contracting skeletal muscle.