Modeling the relation between muscle thickness and wrist angle based on bone-muscle lever model.

Muscle modeling is a powerful tool to study the skeletal muscle, and can give a better perception of the mechanisms of muscular functions. In this study, a mathematical model was proposed based on the bone-muscle lever model to illuminate the non-linear relation between the thickness of extensor carpi radialis muscle and wrist angle. The ultrasound image, SEMG signals were synchronously sampled from the extensor carpi radialis muscle together with the wrist angle during the whole process of wrist extension and flexion to validate the model. The wrist angle was then calculated using the measured muscle thickness by this model. The overall mean correlation coefficient value was 0.96 +/- 0.02, and the overall mean standard root mean square error was 5.82 +/- 1.95, which were much better than the results of other regression methods. The results show that the wrist angle is well predicted by our model, and it suggests that this model is helpful to study the relationship between internal muscle structural changes and external limb behaviors.