AN IMPROVED METHOD FOR MUSCLE FORCE NEUROMUSCULAR DISEASE ASSESSMENT

We describe here the reliability and validity of methods to quantify i nvoluntary muscle torque induced by non-invasive nerve stimulation. A rigid apparatus was used to hold the subject's limb in a predetermined position and confine movement to a specific direction (i.e. ankle dor siflexion or thumb adduction). An incorporated strain gauge was used t o measure isometric torque, and all data were recorded by a data acqui sition program. The innervating nerves were stimulated by surface elec trodes, using either single stimuli to generate a twitch, or short tra ins of stimuli to produce tetanic contraction of the individual muscle under study. The average peak tetanic torque generated by the dorsifl exor muscles in healthy control was 20.4 +/- 3.8 Nm and varied by 3.7% with repeated testing. The mean torque generated by the adductor poll icis muscle in controls was 1.5 +/- 0.4 Nm and varied by 4.6% with rep eated testing. In patient populations significant changes in activated torque were readily quantified, and the effects of treatment cart be easily assessed. Furthermore, several specific parameters of recorded isometric contractions were measured; e.g. time between stimulus and t orque onset, peak rate of torque development, time to peak torque, hal f-relaxation time, and others (none of which are measurable when using voluntary contraction of muscle). Compared to current assessment meth ods, monitoring muscle torque generated by nerve stimulation improves objectivity, reliability, and quantitative capabilities. The presented method has significant potential both in diagnosing neuromuscular dis orders and determining treatment efficacy.