Figure 1. Illustration of the experimental setup for the force task (A) and the position task (B).

Each subject was seated upright with the right hand positioned in the custom apparatus, and faced a monitor for visual feedback. The custom-designed device consisted of a wheel connected to a force transducer (a) or inertial load (b) by means of a pulley and nylon line. The index finger was attached to a bar that was connected to the wheel so that the rotational axis of the metacarpophalangeal joint approximated that of the wheel. Subjects were required to match either a target force equal to 20% of their maximal force by pushing up against a rigid bar (force task (A)), or a target position corresponding to 10° abduction of the metacarpophalangeal joint while supporting an equivalent load suspended from the index finger (position task (B)). The abduction angle of the metacarpophalangeal joint during the position task was measured with a wire-type displacement meter (c) attached to the wheel.