TECHNIQUE FOR DETECTING MUAP PROPAGATION FROM HIGH-THRESHOLD MOTOR UNITS

A technique was developed to identify the propagation pattern of high-threshold motor unit action potentials (MUAPs) in human skeletal muscles. A linear surface array and a selective needle electrode were used simultaneously for detection of myoelectric signals during a constant-force isometric voluntary contraction. The needle signals were decomposed into trains of single MUAPs and were used to trigger-average the surface signals. After averaging 16 channels of surface signals derived with the linear array electrode, we obtained the propagation of single MUAPs along the muscle fibers. The special quadrifilar needle electrode and the algorithm for decomposing the needle signals made it possible to detect high-threshold MUs recruited at less-than-or-equal-to 57.5% of the maximal voluntary contraction (MVC) during 75% MVC sustained contractions and consequently the propagation pattern of APs from those MUs. The position of the innervation zones within single MUs was estimated from the location of the conduction reversals in the surface myoelectric signals. With this technique, we were able to study the configuration of innervation zones of high-threshold MUs in conjunction with their recruitment threshold.