The purpose of this study is to analyze the grip strength by the girth of upper arm and forearm and their muscle activities by duration of grip strength. The subjects were consisted of 20 healthy adults(10 males & 10 females) who had no medical history of neurological and surgical problems with their arms. Girth of upper arm/ forearm and maximum grip strength for 4sec and 30sec were measured. Muscle activity was by wireless electrode EMG system. Co-relation of girth of upper arm/ forearm was significantly high. Upper arm's muscle activity performed for 4sec and 30sec was significantly high. In this study. It suggests that training of upper arm should be performed with the training of grip strength because both of upper arm and forearm affected grip strength.