Tissue displacement and thickness are useful parameters for quantifying muscle function. These parameters can be obtained using ultrasound with high frame rate and reasonable spatial resolution. However, a conventional hand-held ultrasonic probe that is bulky, rigid, and heavy may not be suitable for continuous muscle monitoring during physical activities. This research aimed to measure tissue displacement and thickness variation during muscle contraction using a wearable ultrasonic sensor. However, the energy of the transmitted ultrasonic waves using the wearable ultrasonic sensor is lower
than that of a conventional probe. In order to overcome this issue, selected signal processing techniques were applied and compared. It was found in the numerical simulation experiments that the frequency-domain techniques, in particular LQ-factorization, had better tracking accuracy than the time-domain techniques. In the in-vivo experiment, ultrasonic signals were acquired at a forearm during isometric contraction. The tissue boundary displacements and thickness changes were successfully obtained