In the foot, the tendons of the tibialis anterior and the tibialis posterior may be identified in the figure. Let the magnitude of the force vectors be given by :
While the angles α and β are specified by :
What is the net force acting on the attachment point Q of the two muscles on the foot ?
First, the force vectors Fa and Fp are written with respect to the Cartesian coordinate system. Clearly
Therefore, the net force due to Fa and Fp acting on point Q equals.