Abstract
In the present paper, we examined the nature of the human's hand forces which were exerted on the rigid objects during voluntary constrained tasks. Experimental observations found that when the force was exerted on the objects arbitrarily, subjects tended to generate force patterns. the derivatives of which had roughly single-peaked, bell-shaped profiles. This was held independent of the stage of skill, the arm postures, and the force directions.
Force coordination was modeled mathematically by defining a virtual trajectory and limb elasticity. The virtual trajectory is the sequence of equilibrium points which the limbs are intended to follow due to the modulable elastic properties of the muscles. Then, it is specified through an optimality criterion that the mean square jerk (rate of change of acceleration) integrated over the virtual trajectory is minimal for all possible choices of trajectories. This is equivalent to assuming that a major goal of motor coordination is the production of the smoothest possible force of the hand. The measured force profiles confirmed the predictions of the mathematical model quantitatively.
