A three dimensional mathematical model of the human knee
Muscle and joint force during locomotion is estimated according to available formulations consistent with available methods of solving the indeterminate problem. In the case of the knee joint direct comparisons of results between several optimization methods proposed in the literature presents difficulties due to largely varying model formulation, input data, algorithms and other issues. The application presented here introduces a new optimization program which includes linear and non-linear techniques allowing greater flexibility in problem formulation. It also increases the variety of cost functions under a unified solution which allows for direct evaluation of factors such as optimization criteria and constraints. The method demonstrates that nonlinear solutions lead to more synergistic activity and in contrast to linear formulations, allows antagonistic activity. Nonlinearity also improves concurrence of EMG activity and predicted forces. Higher joint force predictions are resulting as expected from improved predictions of synergistic-antagonistic activity. The formulation allows for relaxation of the requirement that muscles resolve the entire intersegmental moment which in turn maintains muscle synergism in the nonlinear formulation while relieving muscle antagonism and reducing the predicted joint contact force. These methods allow for more possibilities for exploring new optimization formulations and in comparing the solutions to previously reported formulation. The present study based its input data on healthy subjects volunteering for a variety of walking tasks involving normal walking and turning during walking. Muscle and joint contact forces agree with other published results and the lateral: medial bony contact force distribution is calculated as 1: 2.5.