The purpose of this study was to investigate electromyographic activities of the flexor digitorum superficialis (FDS) and the flexor carpi ulnaris (FCU) by the shape of the ultrasound head. Twelve healthy subjects participated and performed ultrasound therapy with a round head and a long handled head during each 5-minute application. Electromyographic activities of the FDS and FCU were recorded by surface electrodes and normalized by maximal voluntary isometric contraction (MVIC) values. There was no difference in the muscular fatigue of FDS and FCU as determined by the shape of the ultrasound head (p>.05). Without the shape of head, the mean power frequency decreased with the time. There also was no difference in %MVIC of the FDS and FCU as determined by the shape of the ultrasound head (p>.05), but the force exerted exceeded 20%MVIC. There was however a significant difference in the amount of cumulative workload of the FDS and FCU as determined by the shape of ultrasound head (p<.05). The workload was however not affected by the shape of the ultrasound head. Constant static grasp of ultrasound transducer head during ultrasound therapy is considered a high risk factor of work-related musculoskeletal disease.