Physical and Biological Limits of Human Motor Performance

Everyday we see astounding displays of humans and other animals interacting with their environment to achieve a variety of goals. But, there are limits to their capabilities, like when an experienced runner falls, or a squirrel misses the branch it was ambitiously trying to reach. Some limits are imposed by the laws of physics, while other limits arise from materials, control capabilities, and disease, injury or ageing. To understand the factors that limit performance, I present some experimental, computational, and mathematical studies on the dynamics and control of the arm, the leg, and the hand.
    (i) Arm - What governs your choice of underarm or overarm throwing style? We predict strategies for throwing accurately by analyzing how error propagates through projectile flight, and compare the model's predictions against human data. (ii) Leg - How did humans run safely before the invention of the modern running shoe? I present results and an analysis of foot collisions based on measurements from habitually barefoot Kenyan and American runners. (iii) Hand - Simply tapping a surface with your finger poses challenging control problems because of the abrupt change in dynamics upon contact. I present results on how neuromuscular lags limit the ability of humans to deal with such abrupt contacts.
    I conclude with some questions and thoughts on whether animals outperform their robotic counterparts because of or despite the nonlinearities and sloppiness inherent to biology. In turn, how do we extract control and design principles from biology, for use in robotic and prosthetic applications?