The purpose of this study is to determine whether the transcutaneous application of unmodulated high frequency alternating currents could produce a quickly conduction block of peripheral nerve.

In the last years several animal experimental studies have evidenced that high frequency unmodulated currents about 5 KHz can cause a peripheral nerve block. However electric currents with these high frequencies that are usually used for the treatment of pain in humans are interrupted or modulated (i.e. interferential currents).

It has show that the diameter of the nerve it is related with the frequency to produce the conduction block. For this reason the investigators decided to applied 20KHz to observe the effects on maximal manual force and to compare versus sham stimulation.

Only one study has applied 5KHz on experimental pain and they have demonstrated changes in somatosensory thresholds.

Inclusion Criteria:

• Healthy volunteers

Exclusion Criteria:

• Neuromuscular disease.
• Epilepsy.
• Trauma, surgery or pain affecting the upper limb, shoulder girdle or cervical area.
• Osteosynthesis material in the upper limb.
• Diabetes.
• Cancer.
• Cardiovascular disease.
• Pacemaker or other implanted electrical device.
• Take any drug (NSAIDs, corticosteroids, antidepressants, analgesics, antiepileptics, ...) during the study and in the previous 7 days.
• Presence of tattoos or other external agent introduced into the treatment or assessment area.
• Pregnancy