Pain inhibition—the unintended benefit of electrically elicited muscle strengthening contractions

The study investigates whether pain caused by electrical muscle stimulation (NMES) can trigger a pain-relieving response, potentially making NMES more tolerable and improving patient outcomes. It compares NMES to voluntary contractions and noxious electrical stimulation (NxES). Healthy participants underwent NMES, NxES, and volitional contractions. Pain thresholds were measured before and after each condition to assess pain inhibition. The results showed that both NMES and NxES increased pain thresholds, suggesting a pain-reducing effect. The pain reduction occurred regardless of self-reported pain levels, indicating that NMES could offer an unintended benefit of pain relief during muscle strengthening. The mechanisms are likely located in the spinal cord and local tissues.

• 1
  Noxious electrical stimulation (NxES) produced higher pain ratings compared to neuromuscular electrical stimulation (NMES).
• 2
  Both NMES and NxES significantly increased pressure pain thresholds (PPTs) in both knees, suggesting pain inhibition, but not in the finger.
• 3
  Self-reported pain sensitivity correlated with pain experienced during NxES, but pain during NMES and NxES did not correlate with pain inhibition.