Using Dynamics to Optimize Limb Prostheses

The design and fabrication of prosthetic limbs for the lower extremity has changed drastically over the past ten years. New materials and technologies have removed the barriers imposed by heavy and bulky limb components. The weight of prosthetic limbs can now be equal to or less than the intact limb. This raises questions regarding the optimal mass and inertial characteristics in order to minimize energy expenditure and maximize functional performance. The scientific resources for answering these questions come from both coordination dynamics and dynamic touch. Previous research has indirectly investigated the challenge for lower extremity amputees during locomotion by asking how arm/pendulum systems having different preferred frequencies are coordinated. The so-derived tools include a theoretical basis for understanding the phenomena, and dependent variables (e.g., standard deviation of relative phase) to measure stability of oscillations. Dynamic touch, in turn, speaks to how the muscle sense detects properties of limbs or tools relevant to their functionally appropriate control. It identifies object properties (e.g., inertial moments) that are detected, and therefore might be manipulated in testing the optimal mass distribution in prosthetic limbs.