Pain Inhibition With Neuromuscular Electrical Stimulation

Participants are provided visual feedback showing the 20% MVIC force and instructed to produce the target force for 10 s then relax for 50 s. The timing is provided by the research personnel until 10 contractions are completed. Participants rate their pain during each contraction on a visual analog scale. The pain ratings are averaged across all 10 contractions and the average is used in the analysis.

Participants are instructed to relax throughout the NMES contractions. The amplitude of the stimulation is increased until 20 percent MVIC force is achieved and the amplitude is recorded. The timing of the NMES is 12 s on: 50 s off for 10 contractions. The on-time included a 2s ramp up to the target amplitude. Participants rate their pain during each contraction on a visual analog scale. The pain ratings were averaged across all 10 contractions and the average was used in the analyses.

The intensity of the electrical stimulation is increased slowly over 30 s to the maximum tolerated level. Trains of NXES are delivered at the maximum tolerated intensity with a timing ratio of 12 s on: 50 s off for a total of 10 trains. The on-time included a 2s ramp up to the target amplitude. Participants rate the pain during each contraction on a visual analog scale. The pain ratings were averaged across all 10 trains of NXES and the average is used in the analyses.