Plantar Flexion Muscle Force Estimation With a Soft Wearable Pneumatic Sensor System

In numerous fields that analyze the human body from a biomechanical perspective, the force of muscles could only be indirectly estimated through multiple hierarchical levels, and the limitations in terms of accuracy were clear for each methodology. Accordingly, this study introduces a novel, noninvasive method for estimating muscle force, leveraging the phenomenon that transverse muscle stiffness increases under more longitudinal tension. By manufacturing the soft pneumatic sensor system for plantar flexor, the two-step model that can fully describe the interaction between the air cell and muscle is developed. Initially, equations incorporating geometric constraints and force equilibrium are derived to calculate the muscle's deformation depth from the measured pressure. The correlation between muscle fiber deformation and the transverse reaction force is then identified. Using the proposed model, pressure measurement from sensor system is converted to force estimate. Experimental validation demonstrates its high estimation accuracy, supporting the effectiveness of the proposed model-based approach. This methodology shows promise for diverse fields that require noninvasive and accurate plantar flexor muscle force estimation.