Impact of Abducting at the Shoulder on Perceiving Torques about the Elbow.

Literature indicates that an individual's perception of their self-generated torques is largely influenced by their descending motor commands. These studies often rely on between-limbs matching protocols, which can introduce confounding factors when interpreting results from populations with unilateral impairments. Here, we demonstrate how changes in descending motor commands impact one's perception of torques using a single-arm protocol. Thirteen participants generated and perceived 25% of their maximum voluntary torque (MVT) in elbow flexion while simultaneously abducting at their shoulder to 10%, 30%, or 50% of their MVT in shoulder abduction (MVTSABD). Subsequently, the participants matched the elbow torque without feedback and without activating their shoulder. The accuracy in matching the elbow torque was influenced by the extent to which the shoulder abducted (p=0.002); the average error in matching elbow torques was greatest at 50% MVTSABD (3.9 ± 4.9 Nm), followed by 30% MVTSABD (2.1 ± 2.7 Nm), and then 10% MVTSABD (0.0 ±2.1 Nm). These results indicate that perception of a torque about the elbow is influenced by the extent of simultaneous activation about the biomechanically-coupled shoulder. Therefore, this approach can quantify, using a single arm, the impact of changes in muscle activation on torque perception.