Comparison between EMG to force processing and kinetic analysis for the calf muscle moment in walking and stepping.
In EMG to force processing the force of a muscle or the corresponding muscle moment with respect to the joint is determined from EMG and muscle length by means of a model of the muscle's contractile and elastic properties. In kinetic analysis the joint moment is calculated from the ground reaction force and the positions and accelerations of the body segments by means of Newtonian equations, based on a rigid body segment model. These two fundamentally different methods have been compared by determining simultaneously the calf muscle moment and the total ankle moment in walking at slow, moderate and fast speed and in stepping up and down a low bench. As long as there is no activity of other muscles, the moments obtained by either method should be identical. The analysis was restricted to such periods, as assessed from the EMG of tibialis anterior. In each experimental condition three steps were analyzed in five subjects of 21-22 yr. In comparison with the results of kinetic analysis, EMG processing shows differences between 7 and 54 Nm r.m.s., with an average of 22 Nm r.m.s. Normalized with respect to the r.m.s. value of the moment itself, the differences amount to 0.13-0.51, with an average of 0.22. In the majority of cases there was no systematic deviation between EMG processing and kinetic analysis and the r.m.s. difference was of the same order of magnitude as determined previously in ergometer experiments.