Electrical Stimulation Devices: Does Shock Have Value?

by Margaret Wahl

You may have seen the ads on the Web, or read the endorsements by actor-director Christopher Reeve, and wondered whether electrical stimulation devices designed to stimulate muscle would do any good in neuromuscular disorders.

These devices deliver what amounts to an electric shock to muscle tissue, usually via nerves that run from the spinal cord to the muscle. Theyre advertised as slowing or reversing muscle atrophy (shrinkage) or re-educating the nervous system so that coordinated movements improve. (These products are different from nerve-stimulating devices that claim to provide pain relief, often known as TENS units.)

Greg Carter

Physical medicine and rehabilitation specialist Greg Carter, co-director of the MDA/ALS Center at the University of Washington in Seattle, has very limited enthusiasm for the muscle-stimulating devices. He admits they may do some good in spinal cord injuries like Reeves.

But, Carter says, spinal cord injury and neuromuscular diseases arent even "apples and oranges." Theyre so different they might be better compared to "apples and freight trains."

In spinal cord injury, he says, theres a break in the connection between the brains nerve cells and those of the spinal cord. Other than this break, the nervous and muscular systems are perfectly healthy.

In contrast, he notes, neuromuscular diseases typically damage much of
the nervous system or the entire musculature.

Nerve Diseases

For the person with a disorder of the peripheral nerves, such as Charcot-Marie-Tooth or Dejerine-Sottas disease, or Friedreichs ataxia, such stimulation is entirely impractical, Carter says.

To be effective, it would have to bypass the abnormal nerves and stimulate muscle tissue itself. That, he says, wont give you a meaningful muscle contraction.

"Electrical stimulation has limited potential if the nerve is abnormal," Carter says, "because the signal doesnt go anywhere. If you just shock the muscle, you can only depolarize [stimulate] a very small area of the muscle. If you send a signal down the nerve, it goes to all parts of the muscle."

In disorders of the motor neurons (muscle-controlling nerve cells), such as amyotrophic lateral sclerosis and spinal muscular atrophy, Carter is also pessimistic.

Muscle Diseases

When it comes to muscle diseases like the muscular dystrophies, Carter and others are even more negative about electrical devices.

He notes that electrical stimulation is harsher and potentially more damaging than natural muscle stimulation, especially if the muscle is already compromised.

"Electrically stimulating the muscles to contract is not the same thing physiologically as normal, voluntary contraction," Carter says.

In a normal contraction, the brain tells the muscle how much force is needed to perform an action, and muscles arent overtaxed. "The number of motor units involved a motor neuron and the muscle fibers it stimulates gradually increases, as does the rate at which the motor neurons fire," Carter says.

By contrast, "When you stimulate with electricity from the outside, everything comes in all at once. Its like pushing the pedal to the metal and racing the engine at top speed, as opposed to the slow, purposeful and controlled acceleration that occurs with voluntary contraction."

The result could be overstressing of muscles an especially bad idea for muscles already weakened by disease.

George Karpati

MDA research grantee George Karpati, a neurologist at the Montreal Neurological Institute of McGill University, agrees.

"In Duchenne muscular dystrophy, for example, where the surface membranes of the muscle fibers are abnormally vulnerable, the forced contraction from electrical stimulation could be damaging," he says.

Hes also concerned about using an electrical device in inflammatory muscle diseases, particularly dermatomyositis, where small blood vessels are destroyed and muscle tissue ends up lacking a sufficient blood supply. With electrical stimulation from an outside source, the demand for energy production placed on such a "malnourished" muscle might be too great, Karpati says.

He speculates that such damage could also occur in association with these devices in metabolic diseases, because energy demand can easily exceed supply in these conditions.

No Quick Fix

So, why do people flock to devices like electrical stimulators?

"People like something you can feel immediately," Carter says. "Electrical stimulation, like large caffeine doses, gives you the feeling of a big effect, and people like that. Coenzyme Q probably has more of an effect at the cellular level than electrical stimulation, but you cant feel it."

Karpati says, "Massage and electrical stimulation may create a subjectively pleasant experience and thus optimism, and many people will shop around until they find a doctor that believes in what they want to use."

Carter believes theres "no pressing medical reason to prevent atrophy.

"If there were a cure for muscle disease, the muscles would regenerate rather quickly except in areas where theres a lot of fibrosis [scar tissue]."

In nerve diseases, including ALS, Carter thinks the muscles would come back even more dependably if the nervous system returned to normal.