Figure 1.

The expected influence of cocontraction on the Cartesian net force f and stiffness k at the fingertip (exemplary). The theoretically achievable force–stiffness range of an antagonistic system consisting of a set of joints actuated by two flexor and two extensor muscles (assumption: linear dependence between force and stiffness of a single muscle). The field is defined by the vector sum of the single muscle curves. Uniform cocontraction leads to an increase in force and stiffness along a line pointing in the direction of maximum stiffness (green), and isometric cocontraction leads to an increase in stiffness, but not in Cartesian net force (blue).