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

Background

High-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.

Findings

Transcutaneous 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.

Conclusions

These 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 registration

NCT, NCT03169049. Registered on 30 May 2017

     

Estimating bone mineral content based on different types of muscle strength tests

The aims of this pilot study were to verify which muscle strength tests better explain bone mineral content (BMC) of the femoral neck and lumbar spine and to develop predictive equations to estimate femoral neck and lumbar spine BMC. Twenty-nine subjects aged 56–76 years old (12 women and 17 men) participated in the study. Femoral neck and lumbar spine BMC was evaluated by Dual X-ray absorptiometry (DXA). Muscle strength measurements included maximal isometric voluntary contractions of knee extensors and flexors, vertical jump, 5-repetition maximum of the leg press (5-RM_LP) and seated leg curl (5-RM_LC), and handgrip strength. Women presented a moderate to strong correlation between femoral neck BMC and 5-RM_LP (r = 0.819), 5-RM_LC (r = 0.879), knee extensors peak torque (r = 0.699), and handgrip strength (r = 0.663), as well as between lumbar spine BMC and the 5-RM_LP test (r = 0.845) and manual grip strength (r = 0.699). For females, the 5-RM_LP and 5-RM_LC tests most fully explained femoral neck BMC (R² = 0.859) and the 5-RM_LP test and body mass explained lumbar spine density (R² = 0.757) for females. Men did not present correlations between BMC and strength variables. For females, the 5-RM_LP and 5-RM_LC variables explained the variations of femoral neck BMC, while 5-RM_LP and body mass explained lumbar spine BMC. Future studies should evaluate a larger sample size and prioritize the strength tests with a greater predictive capacity.