Effects of antecedent TENS on EMG activity of the finger flexor muscles and on grip force

Abstract

Objectives. To examine the effects of unilateral and bilateral application of low-dose high-frequency transcutaneous electrical stimulation (TENS) on EMG activity of the finger flexor muscles and on grip force in the right upper extremity.Methods. Twelve healthy volunteers received unilateral, bilateral, and placebo (zero intensity) TENS stimulation to the finger flexor muscles in three separate sessions. TENS was delivered for 15 min at 100 Hz, with the amplitude adjusted to the sensory threshold. Testing of the right upper extremity was performed in each session prior to stimulation (pre-test), immediately after stimulation (post-test1), and after a 15-min break (post-test2) which followed post-test1. Outcome variables were EMG activation level and maximal grip force.Results. Unilateral and bilateral TENS stimulation were associated with a significant increase in EMG activity of the finger flexors, both at post-test1 and at post-test2, while no change was recorded following the placebo stimulation. The differences between the effects of unilateral vs bilateral stimulation were not significant. Regarding grip force, enhancement at post-test1 was mainly observed following the unilateral and bilateral stimulation, but not after the placebo stimulation. Yet, at post-test2, force enhancement was significant for all three stimulation conditions.Conclusions. The application of 15 min of TENS stimulation may contribute to subsequent muscular activation level and voluntary force production.Significance. The findings of this preliminary study justify further research on the clinical potential of TENS stimulation to affect voluntary motor output during rehabilitation.