Tracking Muscle Stiffness During Gripping With Wearable Ultrasound Shear-Wave Elastometry

This letter presents a wearable ultrasound shear-wave elastometry (wUS-SWEM) device and demonstrates its capability to track time- and depth-resolved muscle stiffness, using grip force as a reference for muscle activation.Shear waves were generated by a miniature actuator and detected using two unfocused ultrasound transducers integrated into a compact, wearable form factor. The device was applied to monitor the forearm flexor muscles during a cyclic grip–relax task, yielding spatiotemporal shear modulus patterns aligned with task timing. In the superficial flexors region, shear modulus exhibited a strong linear correlation with grip force ($\text{r} = 0.82\text{--}0.86$, $\text{p}< 0.001$), supporting its use as a noninvasive predictor of muscle force. These results demonstrate the feasibility of shear modulus tracking during functional activity of the upper arm using wUS-SWEM and highlight its potential for neuromuscular assessment and human–machine interfacing.