The most satisfying results normally are obtained from treatment that is begun at the first sign of inflammation. It is known that ultrasound can stimulate acupuncture points and trigger points for pain relief. The gamma efferent fibers originate in the spinal cord and terminate in specialized muscle fibers called the intrafusal fibers. Vigorous muscle contractions heighten the electrical activity between the muscle and the spinal cord. Impulses traveling from the spinal cord through the gamma fibers to the intrafusal fibers cause the muscle to contract.
Contraction stretches an organ called the muscle spindle.
Stretching of the muscle spindle results in reflex contractions of the muscle fibers. The ischemia causes pain. Pain brings about reflex muscle activity and a vicious cycle called muscle spasm is born. Heating of the gamma fibers slows their transmission rate, which reduces the stimulation of the muscle spindle, allowing the muscle to relax. Heating the muscle tissue also causes an increase in circulation, thus breaking the cycle.