Kinematic features of unrestrained vertical arm movements

TLDR

The study used a three‑dimensional Selspot tracking system to record unrestrained arm movements between point targets in a vertical plane under varying speeds and hand‑held loads. The authors found that, contrary to prior emphasis on straight hand paths, certain movement regions produced curved trajectories, yet all movements—curved or straight—exhibited an invariant tangential velocity profile when normalized for speed and distance, suggesting a simplification of underlying arm dynamics extending previous work by Hollerbach and Flash. Citation: Cybern.

Abstract

Unrestrained human arm trajectories between point targets have been investigated using a three-dimensional tracking apparatus, the Selspot system. Movements were executed between different points in a vertical plane under varying conditions of speed and hand-held load. In contrast to past results which emphasized the straightness of hand paths, movement regions were discovered in which the hand paths were curved. All movements, whether curved or straight, showed an invariant tangential velocity profile when normalized for speed and distance. The velocity profile invariance with speed and load is interpreted in terms of simplification of the underlying arm dynamics, extending the results of Hollerbach and Flash (Hollerbach, J. M., and T. Flash (1982) Biol. Cybern. 44: 67-77).