Effect of high-frequency alternating current transcutaneous stimulation over muscle strength: a controlled pilot study

Abstract

BackgroundHigh-frequency alternating currents of greater than 1 kHz applied on peripheral nerves has been used in animal studies to produce a motor nerve block. It has been evidenced that frequencies higher than 5 kHz are necessary to produce a complete peripheral nerve block in primates, whose nerve thickness is more similar to humans. The aim of the study was to determine the effect on muscle strength after the application of a high-frequency stimulation at 5 and 10 kHz compared to sham stimulation in healthy volunteers.FindingsTranscutaneous stimulation at 5 kHz, 10 kHz and sham stimulation were applied to eleven healthy volunteers over the ulnar and median nerves for 20 min. Maximal handgrip strength was measured before, during, immediately after the intervention, and 10 min after the end of intervention. The 10 kHz stimulation showed a lower handgrip strength during the intervention (28.1 N, SEM 3.9) when compared to 5 kHz (31.1 N, SEM 3.6; p < 0.001) and to sham stimulation (33.7 N, SEM 3.9; p < 0.001). Furthermore, only stimulation at 10 kHz decreased handgrip strength when compared to baseline.ConclusionsThese findings suggest high-frequency stimulation has an inhibitory effect over muscle strength. Future studies are required in patients that are characterized by motor hyperactive such as spasticity or tremors.Clinical trial registrationNCT, NCT03169049. Registered on 30 May 2017

20-kHz alternating current stimulation: effects on motor and somatosensory thresholds

“…In a previous study conducted by our group, 5 kHz HFAC stimulation applied over the radial nerve for 20 min produced similar modulatory effects on somatosensory thresholds when compared to transcutaneous electrical nerve stimulation (TENS) [7]. Another pilot study demonstrated a larger decrease in maximal handgrip strength during 10 kHz HFAC of the median and ulnar nerve, when compared to either a 5 kHz or sham stimulation [14]. Similar results have been shown by Kim et al [10], reported an increase in mechanical detection threshold (MDT) and pressure pain threshold (PPT) after 10 kHz HFAC stimulation of the median nerve, and an additional decrease in finger muscle contraction during the stimulation.…”

“…To date only four published studies have reported the effects of non-invasive transcutaneous HFAC stimulation over peripheral nerves [7,10,11,14]. In a previous study conducted by our group, 5 kHz HFAC stimulation applied over the radial nerve for 20 min produced similar modulatory effects on somatosensory thresholds when compared to transcutaneous electrical nerve stimulation (TENS) [7].…”

“…The evaluation included measures A, B and C (see section D. Outcome measures) assessed throughout the experiment at four time points: i) before stimulation (0 min), ii) during stimulation at 15 min (15 min), iii) at the end of the stimulation (20 min) and iv), at 10 min after the end of the stimulation (30 min). A washout period of 24 h was used between the application of the two interventions [14].…”

“…Two surface self-adhesive electrodes 5 cm × 5 cm (ValuTrode, Axelgaard Manufacturing Co, LTD, Fallbrook, USA) were used. The proximal electrode was fixed to the skin over the path of the ulnar nerve at the epitrochlea and the distal electrode was placed on the median nerve over the carpal tunnel [14]. The same stimulator device was used to apply the two interventions (Myomed 932, Enraf-Nonius, Delft, Netherlands), whose software was previously modified to be able to deliver an electrical current of 20 kHz.…”

“…5401 GRIP-D Takei Scientific Instruments CO., LTD. Shinagawa-ku, Tokyo). Average maximal handgrip muscle strength was calculated as mean of three measurements and used for statistical analysis [14] (Fig. 1a).…”