The influence of stimulation pulse frequency on the generation of joint moments in the upper limb

Six muscles of the upper limb were stimulated transcutaneously. The influence of the stimulation pulse frequency on the isometric joint moment generated by each muscle is reported. A lower frequency of stimulation, the critical fusion frequency, was found for each muscle at which contractions ceased to be tetanic. This fusion frequency was correlated with muscle function. The magnitude of the joint moment was examined as a function of the stimulation pulse frequency for the six muscles tested. Parabolic curves were found to fit this relationship best, the magnitude of the moment reaching a maximum at typically 50 Hz and often decreasing at higher frequencies. The slope of the linear portion of the relationship between the generated joint moment and the stimulation current intensity was shown to be a function of the stimulation pulse frequency.