Experimental paradigm.

<p><b>A.</b> The white bar represented the target force level which was set at the beginning of each trial to 5%, 25%, or 50% of each subjects’ MVC. A second red/green force bar was controlled by the subject and provided real-time visual feedback of their force production during active conditions, or moved according to a pre-recorded force trace during passive conditions. The bar was red during rest periods and green when the subject had to produce force or view the pre-recorded force trace. When the force bar turned green, the subject’s goal was to match the green bar with the white bar. Each trial was 15s long, and included 5 force pulses. Each pulse was 1.8s (bar turns green) and pulses were separated by a 1.2s rest period (bar turns red). Trial timing was the same during passive conditions but subjects were instructed to view the green bar and not produce any force. The pre-recorded force trace was collected during each participant’s practice session. Each 15s trial was followed by a 7.5s rating period. Subjects rated the level of stimulation they experienced during the previous 15s trial. Ratings were made using a button box to control a cursor on a visual analog scale (VAS) presented on the screen. <b>B</b>. Example force traces (black lines – left y-axis) and temperature traces (red lines – right y-axis) from active trials from one subject for the hot condition at 5%, 25%, and 50% of MVC.