Sensory transcutaneous electrical stimulation fails to decrease discomfort associated with neuromuscular electrical stimulation in healthy individuals

Objective: Sensory transcutaneous electrical nerve stimulation (TENS) is frequently used for pain modulation. Neuromuscular electrical stimulation used to induce strong muscle contractions is often limited by muscular discomfort and by discomfort associated with the electrical current. The objective of this study was to determine whether the application of TENS can reduce the discomfort associated with neuromuscular electrical stimulation, leading to stronger maximal electrically induced contractions. Design: In a double-blind randomized controlled trial, 24 young adults with no known impairment received a TENS and a sham treatment before and after the assessment of the maximal electrically induced contractions of the quadriceps muscle. Results: Sensory TENS had no significant effect on maximal electrically induced contractions (normalized to maximal voluntary isometric contractions), on current amplitude, on the discomfort associated with the muscle contraction, and on the discomfort associated with the current amplitude (the latter two rated using a numerical rating scale). The discomfort described as a pulling/tearing sensation of the muscle (mean [SD], 5.7 [1.6]) was significantly higher than the discomfort associated with the current amplitude (mean [SD], 4.6 [2.3]; P = 0.02). Conclusions: Sensory TENS was not effective in modulating the discomfort associated with neuromuscular electrical stimulation in individuals with no known impairment. During periods of maximal electrically induced contractions, the pulling sensation of the muscle is generally more disconcerting than the sensation of the electrical current. Further studies are necessary to determine the effect of different stimulation parameters in patients with pathologic conditions.