Three-dimensional moment and stiffness summation for muscles sharing a common tendon

This study examined the hypothesis that muscles operating in the normal physiological state act as independent actuators. This hypothesis was tested by measuring the nonlinearities associated with three-dimensional (3D) moment and stiffness summation for three muscle groups crossing the cat ankle joint. Our results indicate that the nonlinearities associated with joint moment and stiffness summation are small (<5%), even between muscles having extensive myofascial interconnections.