Examining the Impact of Wrist Mobility on Reaching Motion Compensation Across a Discretely Sampled Workspace

This paper presents an effort to characterize the impact of wrist mobility on reaching motion compensation over an evenly sampled planar workspace. When the degrees of freedom of the arm are limited due to injury or amputation, the behavior of other joints is modified to achieve the same motion goals. Though several past studies have measured motion compensation for simulated activities of daily living, the results tend to be specific to one spatial configuration of user and objects. Conversely, this paper aims to understand how motions and compensation vary when the same task (reaching-and-grasping) is conducted at a variety of locations across in the workspace. This high-resolution sampling enables spatial patterns of unimpaired and impaired movement to be identified. To achieve this, joint angles and Cartesian trajectories of the upper body were recorded as able-bodied participants reached and grasped 49 (7×7) equally spaced vertical cylindrical targets on a 1.9xl.9m grid, using their dominant hand. This was first completed naturally and then while wearing a custom orthopedic arm brace, which limits all 3DOF (degrees of freedom) of wrist motion. Each reaching motion was segmented and independently analyzed using metrics for range of motion, and Cartesian path length of body segments. A spatial `heat-map' display approach visually indicates how regions of the workspace affect the behavior of different body joints and segments. Further statistical analysis quantifies these visual trends. The results indicate wrist mobility has significant impact on shoulder and elbow ROM in addition to the length of Cartesian motion trajectories for the wrist and elbow.