Dealing with constraints: a biomechanical approach

Quantitative observations are presented on how normal human subjects manipulate a loaded crank. Velocity patterns showed that the task was performed smoothly, despite kinematic singularities which required rapid, precisely timed reversals of joint motion. Significant forces were exerted normal to the crank such that the crank partially supported the weight of the arm. Kinematic data revealed that arm motion depended on the direction of crank motion. These observations suggest that humans use a task-oriented control strategy and may take advantage of motion constraints to reduce required effort