FNS is the use of low-voltage electricity to elicit a skeletal muscle response. The electrical excitability of the nerves and muscle tissue provides the basis for its therapeutic use. Normally, movement of the extremities originates in the motor areas of the brain. For various reasons, such as trauma, stroke, neurological disease (e.g. multiple sclerosis), congenital deficiencies, or tumor, the neural pathway between the cerebral cortex and the muscles may be disrupted or damaged.
The basic premise of functional neuromuscular stimulation is that a viable muscle, even though atrophied, can still be activated and controlled by means of electrical stimulation applied below the level of injury.
In addition to eliciting contraction of skeletal muscles, electrical stimulation has also been employed in a variety of other applications, such as to contract the heart muscle (i.e., cardiac pacemakers), alleviate pain (TENS units), improve bladder control, control epileptic seizures, prevent the progress of scoliosis, promote bone strength, improve blood circulation in various parts of the body, control respiration, and stimulate the auditory nerve and visual cortex.