Muscle recruitment with intrafascicular electrodes

The authors have studied muscle recruitment with Teflon-insulated, 24 mu m diameter, Pt-Ir intrafascicular electrodes implanted in nerves innervating the gastrocnemius and soleus muscles of cats. The purpose was to measure the performance of these bipolar electrodes, which were designed to optimize their ability to record unit activity from peripheral nerves, as stimulating electrodes. Recruitment curves identified the optimal stimulus configuration as a biphasic rectangular pulse, with an interphase separation of about 500 mu s and a duration of about 50 mu s. The current required for a half-maximal twitch contraction was on the order of 50 mu A. Current and charge densities needed for stimulation were well below levels believed to be safe for the tissue and electrode materials, involved. The spinal reflex contribution was not the same in all the implants.