1 Electromyography (EMG) has been widely used for the assessment of 2 musculoskeletal functions and the control of electrical prostheses, which make use of the 3 EMG signal generated by the contraction of the residual muscles. In spite of the successful 4 applications of EMG in different fields, it has some inherent limitations, such as the 5 difficulty to differentiate the actions of neighboring muscles and to collect signals from 6 deep muscles using the surface EMG. The majority of current EMG controlled prostheses 7 can only provide sequential on-off controls using signals from two groups of muscles, so 8 the users are required to put many conscious efforts in monitoring the speed and range of 9 motion of the terminal devices being controlled. Recently, many alternative signals based 10 on the detection of dimensional changes of muscles or tendons during actions have been 11 reported. The objective of this study was to investigate the potential of the dimensional 12 change of muscles detected using sonography for musculoskeletal assessment and control. 13 A portable B-mode ultrasound scanner was used to collect the dynamic ultrasound images 14 of the forearm muscles of six normally-limbed young adults and three amputee subjects. A 15 motion analysis system was used to collect the movement of the wrist angle during the 16 experiments for the normal subjects. It was demonstrated that the morphological changes of 17 forearm muscles during actions can be successfully detected by ultrasound and linearly 18 correlated (R 2 = 0.876±0.042, mean±SD) with the wrist angle. We named these 19 sonographically detected signals about the architectural change of the muscle as 20 sonomyography (SMG). The mean ratio between the wrist angle and the percentage 21 deformation of the forearm muscle was 7.2±3.7 deg/% for the normal subjects. The 22 intraclass correlation coefficient (ICC) of this ratio among the three repeated tests was 23 0.868. The SMG signals from the residual forearms were also successfully detected when 24 3 the three amputee subjects contracted their residual muscles. The results demonstrated that 1 SMG had potentials for the musculoskeletal control and assessment. 2 3 4

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