There are several types of electrotherapies: TENS, Electroacupuncture (TENS on active acupoints), and PENS (percutaneous electrical nerve stimulation, which is TENS applied to needles inserted into active acupoints). TENS, PENS, and EA all stimulate the release of natural neurochemicals (such as endorphines) in the CNS, but PENS also causes the local effects of needling, such as activation of the immune system.
All three stimulate A-beta and A-delta nerve fibers causing a frequency-dependent endorphin release. Remember that the input of pain signals come from C- and A-delta fibers and this input can be modified from A-beta fibers before the pain signals reach the brain. Endorphin release from stimulation of the A-beta and A-delta fibers strongly inhibit the incoming pain signals.
So far, we know that low frequency stimulation [2Hz] stimulate the release of endomorphin and enkephalin while high frequency stimulation [100 Hz] stimulates the release of dynorphin. Beta-endorphin is initially stimulated at 2Hz and its release is inversely proportional to frequency. In addition to the release of enogenous opioids, other neurochemical analgesic factors are triggered by TENS/EA/PENS, such as serotonin and norephinephrine.
In addition to endogenous endorphins, TENS/EA/PENS also stimulate the release of anti-endorphins, which reduce the analgesic effect. High frequency stimulation causes a greater release of the anti-endorphins, which is why frequencies between 2 - 5 Hz are normally used, although some believe a mixed/alternating frequency between 2Hz and 100Hz elicits the greatest release of endorphins. Also, prolonged stimulation [approaching 3h] causes the release of anti-endorphins, which reduces the analgesic effect.
Loosely referenced from: Clinical Acupuncture:Scientific Basis by G. Stux and R. Hammerschlag (Eds) and Biomedical Acupuncture for Pain Management: An Integrative Approach by Ma et al.
Last edit by Josh L.Ac. on Apr 28, '07
: Reason: Sources