The purpose of this study was to investigate the differences of the motion and muscle activity between skilled and unskilled subjects during sharpening kitchen knife. Two skilled subjects and one subject with no experience of sharpening a knife were asked. Their motions were recorded by 4 cameras (60Hz) and surface EMGs were recorded from 4 muscles of both upper limbs. The skilled subjects had shorter motion duration, longer motion pathway, and higher reproducibility in each stroke than the unskilled subject. In each stroke prominent EMG activities in extensor carpi ulnaris, triceps brachii, and deltoid muscle were observed in the skilled subjects. We also examined the shape of the sharpened knife blade of each subjects closely under a microscope. The front edge and central region of the knife sharpened by the skilled subjects changed odd-shaped, while those by the unskilled subject remained unchanged.
