New method using multi-regression analysis on evoked electromyography during movement to adjust stimulation conditions

A new method of stimulation of the lower extremities was devised that automatically adjusts the stimulation conditions at any angle of the knee joint. An M-wave is considered to indicate the stimulation conditions, because it is the wave-form that results from direct stimulation to the axon of the alpha motor neuron. The present device adjusted the stimulation intensity, using multi-regression analysis to evoke an M-wave of preset amplitude. Participants included five people without any neuromuscular impairment. The subjects sat on a chair during the test. The hip joint was fixed at a flexion angle of 90°, and the ankle joint was fixed at the midposition. During passive knee joint movement ranging from 0° to 135°, M-waves were measured. Electrodes were attached at the popliteal fossa and the patella to stimulate the tibial nerve. Ag-AgCl electrodes were put on the belly of the right soleus muscle for the M-wave measurement. The device was set to give M-waves close to the preset value, 10%Mmax. According to previous research, the allowable limit of M-wave amplitude deviations was reported to be about 5%Mmax. The M-wave amplitudes evoked by the device were in the allowable range (9.2±2.5%Mmax). The device enabled control of the M-wave amplitude over the entire range of motion of the joint. Using this device, it was possible to examine the excitability of the alpha motor neuron pool more precisely.