Pulsed magnetic field of about 20 cycles per second. I have one that does 10 hz, but it doesn’t have the same effect. A pulsed magnet field induces a voltage in the tissue if it is strong enough.
I’ve seen youtube videos of therapeutic pulsed magnetic fields being used on horses, that were so strong that it caused the muscles to visibly contract with each pulse. That muscle contraction was produced by the magnetic field creating induced voltage, or at least thats what I presume is the mechanism.
If you do a google search of pulsed magnetic fields, you will find that a lot of research has been done. What they find is different frequencies have different physiologic effects. The lower frequencies, like 20 hz and below tend to have healing effects where the higher frequencies have disruptive effects.
For example, 10 hz will accelerate healing of nervous tissue, turn off apx 130 genes associated with aging and turn on about the same amount for regeneration. There were studies that PMF will accelerate healing of bone and reverse osteoporosis, I think it was about 20 hz, but not sure if that is correct.
