SENSATION OF STATIC FORCE IN MUSCLES OF DIFFERENT LENGTH

Five subjects matched a series of static contractions of a muscle with simultaneous contractions of the contralateral muscle. Matching experiments were conducted with adductor pollicis, biceps, and triceps muscle pairs. Individual muscle lengths were varied thereby altering maximal force according to the length-tension relationship. Maximal voluntary contraction (MVC) and ulnar nerve stimulation produced greatest forces at the same length. Excitatory input was monitored from smoothed rectified electromyograms (SREs); the measure of sensation was matching force. In two muscles with the same MVC, the slope of the function relating reference and matching forces was about 1.0. Slopes of functions obtained from muscles with unequal MVCs were proportional to the ratio of MVCs. Differences in MVC were accompanied by significant differences in the slope from 1.0 but the intercepts did not differ from zero. Corresponding SRE relations during these trials were not influenced by muscle length indicating a constant excitatory input for a given level of sensation. These data suggest that the conscious sensation of force from human skeletal muscle contraction depends primarily on the central command to muscle and is only slightly modified by feedback from peripheral receptors. © 1979.