Pain Inhibition With Neuromuscular Electrical Stimulation
Condition: Healthy Participants
Study type: Observational

Summary: 
      The purpose of this study is to demonstrate the pain relieving effect of neuromuscular
      electrical stimulation that is applied for the purpose of increasing muscle force output.
    

Detailed description: 
      Electrical stimulation (ES) is used by physical therapists during treatment of many
      conditions including muscle weakness and pain. Neuromuscular electrical stimulation (NMES) is
      used to produce strength gains, but it is uncomfortable. The discomfort is thought to limit
      its acceptability by patients. Transcutaneous electrical stimulation (TENS) is the
      application of ES for pain relief. The intensity of TENS is strong but comfortable. The
      nervous system modulates pain in many ways, and one way that it can inhibit pain is through
      conditioned pain modulation; the "pain inhibits pain" phenomenon. Painful experiences can
      elicit inhibitory mechanisms that actually reduce pain. This study is designed to demonstrate
      that NMES elicited muscle contractions produce pain relieving effects that will benefit
      patients over and above the strengthening effects. Participants will be healthy young (18-30
      years of age) who will rate their pain and undergo bilateral quantitative sensory testing of
      pressure pain over the right quadriceps tendon. They will experience three conditions:
      volitional contractions at 20 percent of the maximum voluntary isometric contraction (MVIC)
      force, electrically elicited contractions at 20 percent MVIC, and noxious electrical
      stimulation (NXES) at maximum tolerated intensity applied to the patella to prevent muscle
      contraction. Ten contractions or trains of stimulation will be applied at a ratio of 10
      seconds on 50 seconds off to replicate the typical application of NMES for muscle
      strengthening. The order of the conditions will comprise: volitional contractions and NXES
      will be applied in a random order followed by NMES contractions. NMES was applied last to
      reduce any influence of muscle fatigue. Pressure pain thresholds (PPT) will be measured
      before and after each condition in both knees and the middle finder by applying pressure at a
      rate of 30 kilopascal/s. Participants will indicate immediately when the pressure turns to
      pain and the pressure will be recorded as their pain threshold. This will be repeated 3 times
      and the average of the last 2 measurements will be used in the analysis. Participants will
      rate their pain during the conditions using an 11-point visual analog scales in which 0= no
      pain and 10= the worst pain imaginable. Testing will take place over two sessions, in the
      Motion Analysis Laboratory of the University of New England separated by at least one hour.
      In session 1, participants will be familiarized with any procedures that could cause pain
      including pressure pain threshold testing, NMES elicited muscle contractions and noxious
      stimulation. The MVIC force of the quadriceps will also be measured and used to determine the
      goal force output for the volitional and electrically elicited contractions of 20 percent
      MVIC. In session 2, participants will undergo the testing procedures, each separated by at
      least 1 hour.
    

Intervention name(s): Volitional Contractions (VOL); Neuromuscular Electrical Stimulation (NMES); Noxious Electrical Stimulation (NXES)
Intervention type(s): Other; Device; Device
Intervention description(s): 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.
Observational model: Cohort
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Healthy men and women between 18-30 years of age
      
Keywords: Transcutaneous Electric Nerve Stimulation; Noxious Electrical Stimulation; Pain Threshold; Muscle Contraction; Muscle Weakness; Pain Management; Quadriceps; Strength; Pain Inhibition