Figure 1. Schematic diagram of the experimental protocol.

Three brief control contractions were performed at the level of EMG produced at 25% MVC. During each control contraction, a stimulation sequence was delivered (dotted arrow, open arrowhead) which included a single test stimulus (continuous arrow, filled arrowhead), paired conditioning–test stimuli (continuous arrow, open arrowhead), and a brachial plexus stimulus (dotted arrow, filled arrowhead). This stimulation sequence was also delivered during the sustained 10 min contraction. Ratings of perceived effort and muscle pain (R) were collected during the during the sustained contraction. To assess the fatigue induced by the sustained contraction, a brief MVC was performed ∼5 s afterward.