The biomechanics of force production.

To interact mechanically with the world and especially to use hand tools we exert force. However, the biomechanical consequences of force production can be challenging. In particular, due to the nonlinear kinematics of the mammalian skeleton and of typical hand tools, exerting force can destabilize posture, compromising the ability to control force. In this chapter we present a simplified analysis of this phenomenon that shows how the destabilizing effect of force production varies with pose and tool geometry, and how it may be offset by neuro-muscular stiffness. We also show that in some circumstances the limits of force production may, in fact, be due to a limited ability to produce stiffness rather than a limited ability to produce force. An experimental confirmation of these predictions is presented.