Musculotendon forces derived by different muscle models.

The accuracy, feasibility and sensitivity of several different methods for calculating muscle forces during functional activities in humans were investigated. The upper extremity dynamic system was chosen, where the flexion-extension of elbow joint was studied. To counteract the redundant mechanisms we adopted optimization criteria with and without models of individual muscles according to their active and passive properties. Comparisons with known movements solved by inverse dynamics approach and optimization techniques provided similar results for all optimization criteria. Moreover, if muscle models with active and passive properties are included in these analyses, it is relatively easy to calculate muscle forces of both agonists and antagonists. These approaches may be used to provide input data for dynamic FEM stress analysis of bones and bone-implant systems.