Optimality of human movements in constrained and unconstrained manipulations

Kinematics aspects of planning and control of human arm movements are considered in this paper. First, we analyze unconstrained reaching movements using simple analytical models. Here, we introduce a generalized minimum jerk criterion, analyze the smoothness of the optimal solutions, and discuss the role of the boundary conditions in the trajectory formation, Next we analyze the constrained human movements using a crank rotation task. Analysis of the experimental data shows that constrained and unconstrained reaching movements might involve different control strategies, which is reflected in the choice of the optimality criterion. It is demonstrated that among the kinematics-based criteria the minimum crank jerk criterion produce a rough matching to the experimental data. It is hypothesized that in the process of learning and adaptation the brains constructs a suitable parameterization of the constrained manifold.