Following the results of fundamental studies with animals it is studied in the same way with human subjects. 1) Single motor unit picked up with coaxial needle electrode was analysed with high cut filter and it was shown that there were two kinds of functional specialization, kinetic and tonic motor unit in the EMG. 2) Contents of high frequency components of the kinetic and tonic motor unit at voluntary contraction using the surface electrode was investigated. The forearm muscle contains more kinetic motor unit than the upper arm ones. 3) Proximal muscles in the extremities such as the deltoid were more sensitive to curare than distal muscles for example, the forearm muscles, when metubine (d-tubocurarine iodide) is administered intravenously. 4) It was observed that the kinetic motor unit plays a major role at the initial stage of the contraction.