Physical therapy refers to the use of one or more physical approaches to promote and maintain the body’s well-being, to help a horse recover from injury, and to re-educate an injured body part to move or function normally. Electrotherapy, in particular, is the application of an electric current via surface electrodes to produce controlled movement of the skin, muscle, tendon, and associated ligaments, explains Sheila Schils, PhD (biomechanics/kinesiology), a private equine rehabilitator in Wisconsin who reviewed the use of electrotherapy devices in horses at the 2009 American Association of Equine Practitioners annual convention. There are two main types of electrotherapy devices: sensory nerve or motor nerve stimulator.

Transcutaneous electrical nerve stimulators (TENS) These tools can be used to decrease pain by changing how the nervous system responds to pain signals. In general, TENS units send electrical signals that confuse the pain pathways, blocking the sensation of pain. These systems are designed to stimulate only sensory nerves.

Interferential stimulators These units also are nerve stimulators, but each uses a pair of high-frequency waves that can penetrate deeper into the skin than TENS units. Therapists use these stimulators to treat patients with debilitating pain. "Due to the very uncomfortable sensation of these stimulators, they should not be used for muscle stimulation, only very carefully used for nerve stimulation," says Schils.

Neuromuscular and functional electrical stimulators (FES) These units use electrical waves to stimulate motor nerves (i.e., nerves that control muscles). Thus, neuromuscular stimulators offer a way to mobilize muscles and associated tendons and ligaments through controlled muscular contractions, which can be uncomfortable for the horse. Ultimately, the deep muscle contractions these units induce reduce spasticity and the associated pain in the stimulated muscles. Unlike the TENS and interferential stimulators, this pain relief is long-lasting