An isovelocity dynamometer method to determine monoarticular and biarticular muscle parameters

This study aimed to determine whether subject-specific individual muscle models for the ankle plantarflexors could be obtained from single joint isometric and isovelocity maximum torque measurements in combination with a model of plantarflexion. Maximum plantarflexion torque measurements were taken on one subject at six knee angles spanning full flexion to full extension. A planar three segment (foot, shank and thigh), two muscle (soleus and gastrocnemius) model of plantarflexion was developed. Seven parameters per muscle were determined by minimizing a weighted root mean square difference (wRMSD) between the model output and the experimental torque data. Valid individual muscle models were obtained using experimental data from only two knee angles giving a wRMSD score of 16 Nm, with values ranging from 11–17 Nm for each of the six knee angles. The robustness of the methodology was confirmed through repeating the optimization with perturbed experimental torques (±20%) and segment lengths (±10%) resulting in wRMSD scores of between 13–20 Nm. Hence, good representations of maximum torque can be achieved from subject-specific individual muscle models determined from single joint maximum torque measurements. The proposed methodology could be applied to muscle-driven models of human movement with the potential to improve their validity.