Joint position sense during a reaching task improves at targets located closer to the head but is unaffected by instruction.

The purpose of the present study was twofold. Our first purpose was to test whether joint position sense is similar under instructions to memorize hand position and instructions to memorize shoulder and elbow angles. We hypothesized that instructions to memorize hand position would produce smaller errors due to evidence suggesting that the CNS directly determines hand position but indirectly determines joint angles from proprioceptive information. Our second purpose was to assess biases in joint position sense at various joint angles in a sagittal workspace. We hypothesized that akin to previous single-joint investigations, the shoulder and elbow would demonstrate better joint position sense as joint angles approached 90° during our multi-joint task. Sixteen healthy and right-hand-dominant subjects participated in the present investigation. Subjects were required to actively position their right upper extremity to one of three targets for a memorization period. After returning to the rest position, subjects then actively repositioned back into the target. We did not find evidence of a substantial difference in joint position sense between instructions to memorize the hand position or joint angle. This finding, when considered in conjunction with other evidence, suggests that studies employing either a joint angle protocol or a hand estimation protocol likely produce results that are similar enough to be compared. Proprioception has been shown to be non-uniform across a two-dimensional horizontal workspace. The present investigation provides evidence that proprioception is also non-uniform across a two-dimensional sagittal workspace. Specifically, angular errors decrease as upper extremity joint angles approach 90° of flexion and endpoint errors decrease as targets are located increasingly closer to the head.