アレイ状表面電極による運動単位の発射周波数の計測

抄録

Shapes of motor unit action potentials (MUAPs) of the same motor unit (MU) changed obviously during contractions of muscle, in particular, when the limb was moving. Effects of electrode geometry and configuration on the shape of MUAPs were examined. On the basis of the results, an arrayed (five channel) surface electrode in a bipolar configuration was devised by which MUAP trains could be identified reliably even during limb movement as well as during isometric contraction. EMG activities of human biceps brachialis muscle were measured in voluntary isometric and isotonic contractions with the electrode, and inter-spike intervals of MUAP trains (firing rates) of the single MUs were calculated. The results are summarized below. (1) Shapes of the MUAPs were not affected significantly by the size of a rectangular electrode ranging from 2 to 8mm in both width and length. (2) As the inter-electrode distance of the bipolar electrode became shorter, the duration of measured MUAPs became shorter. This means that shorter inter-electrode distance makes it easier to distinguish accurately the activity of single MUs. (3) Configuration of a 5-channel electrode which made it reliable to identify MUAP trains was determined; three channels were placed in parallel with the muscle fibers with the distance between channels being 10mm. The interelectrode distance was 5mm and the disc electrode diameter was 2mm. Two additional channels were oblique to the muscle fibers. (4) MUAP trains of the single MUs were identified up to 20-40% of the maximum voluntary isometric contraction with the arrayed electrode, and the firing rates were measured. Firing rates of single MUs increased with muscle force. (5) EMG activities were measured in voluntary isotonic contraction over the range in loadtorque from 0.6 to 3.7 Nm and in elbow-flexion velocity from 0 to 30 deg/sec, and then firing rates of single MUs were measured. (6) Firing rates of single MUs were not significantly dependent on the elbow angle in the isotonic contraction within the above-men-tioned range in torque and velocity. (7) Firing rates of single MUs increased with the increase in load-torque and flexion velocity.