Ongoing Projects

A Method to Measure Stiffness During Human Movements Human movements are generally stable due to the spring-like property of muscles. However, movements can become unstable when the limbs interact with the environment, e.g., when one lifts a weight overhead, or carves. The stiffness measured at the endpoint of the limb is indicative of this stability. I have developed a method to measure stiffness during arm movements in collaboration with Ted Milner at Simon Fraser University in Canada and Mitsuo Kawato from ATR International, Japan. A powerful robotic interface displaces the hand during movement relative to a prediction of the undisturbed trajectory. Stiffness is estimated from the restoring force measured during the brief perturbation. Using a specially developed robot stationed at ATR, we can measure arm stiffness during adaptation to arbitrary computercontrolled dynamic environments.