Electromyography (EMG) has been widely used for the functional assessment of muscles. On the other hand, sonography has been commonly used to detect the morphological information of human muscles in both static and dynamic conditions. In this study, we demonstrated the feasibility to use the continuous signals about the architectural changes of muscles detected in real-time from ultrasound images to characterize muscles under isometric contraction. We named this signal as sonomyography (SMG). Synchronized ultrasound images and surface EMG (SEMG) signals were continuously collected from the right biceps brachii during the isometric contraction and subsequent relaxation periods together with the generated torque. The relationships among the SEMG, the muscle deformation SMG and the torque were investigated for the contraction phase. The results suggested that the SMG together with EMG signals may potentially provide a more comprehensive assessment for the muscle functions.