The OpenArm Project: Exploring Deformation as a Measure of Muscle Force

Abstract

While many musculoskeletal simulation frameworks rely on estimates of muscle force, there exists no noninvasive, in vivo method of measuring the force exerted by individual muscles. Instead, forces are estimated based on motion-specific assumptions and/or noisy measures of neural activation. A direct, accurate measure of muscle force would enable improved understanding of dexterity, better quantification of pathology, and safer, more expressive assistive device control. We propose measuring muscle force via muscle deformation, a signal that is intrinsically coupled to force production: as muscles shorten and widen during the cross-bridge cycle, tendons lengthen and force increases. In this work, we present a) evidence that this deformation is observable during voluntary exertion and (when correctly parameterized) is correlated with joint torque; b) preliminary findings on useful signals for force inference; and c) the OpenArm project, an open-source collection of data and analysis code to enable study of the force–deformation relationship by the wider research community.