Measuring muscle stiffness by linear mechanical perturbation

Transverse muscle stiffness provides valuable information regarding the health and activation level of muscle. Current muscle stiffness sensors are either tethered to a benchtop module or designed as hand-held instruments capable of static measurements. We propose a novel wearable sensor, the sarcometer, to continuously measure dynamic transverse muscle stiffness. The sarcometer utilizes a small linear Lorentz force actuator with position sensing to perturb the muscle body. Initial experimentation was performed on the lateral gastrocnemius of one subject during different periods of muscle activation. Experimental force and displacement measurements were used to estimate the dynamic model of the muscle during each condition. The model stiffness was shown to significantly (p <; 0.001) increase from 347 N/m during normal standing to 1606 N/m during standing on the toes of one foot. We hope to further miniaturize the sarcometer into a self-contained system for continuous monitoring of tissue stiffness.