Selective stimulation current – treatment of denervated muscles

What is selective stimulation current treatment?

Selective stimulation current treatment is a form of electrotherapy. It can be used to treat so‑called denervated muscles, i.e. muscles that have lost their motor nerve supply.

This can be caused by various forms of peripheral paralysis: peroneal palsy, facial nerve palsy, herniated disc, nerve injury after a spinal fracture, nerve damaged during spine surgery, etc.

Attention! Some therapists mistakenly treat stroke‑related paralysis with selective stimulation current. However, selective stimulation current is not suitable for stroke patients because it can increase muscle stiffness (in professional terms: it increases spasticity). In stroke the motor nerve supplying the muscle is intact (the problem is at the level of the brain connections). Therefore, stroke‑related paralysis should be treated not with selective stimulation current but with “regular”, biphasic square‑wave muscle stimulation (and low frequency)!

The treatment is called selective because it acts on denervated muscles (lower motor neuron damaged). The denervated impulse is too long for treating healthy muscles. Treating a muscle with an intact motor nerve with selective stimulation current is unpleasant, even painful, and has little effect.

During selective stimulation current treatment, an electrode placed on the skin (adhesive, metal or rubber) delivers an electrical impulse with milliampere (mA) current intensity to the treated muscle, which then contracts. The impulse shape can be triangular, trapezoidal or a square wave. By adjusting its frequency, intensity and duration you can control the type of contraction, how much of the muscle bundle is activated, the speed and the frequency of contractions.

The treatment can be focused on a specific muscle or muscle group, so the effect is limited to those areas.

Normally a muscle contracts in response to an electrical signal coming from your brain. In stimulation treatment the muscle receives similar, artificial impulses.

In both cases the contraction occurs via exactly the same mechanism, the same metabolic processes take place, and the muscle also fatigues in the same way.

Treatment of denervated (motor nerve lost) muscle

This is the application area of selective stimulation current. The chance of recovery for a denervated muscle increases many times if it receives daily selective stimulation current treatment!

Those who do not receive regular stimulation treatment improve little or much more slowly. Stimulation offers the real chance for nerve regeneration and “re‑sprouting”.

You should know that nerve pathways regenerate extremely slowly. Even in optimal conditions with continuous stimulation they grow at most about 1 mm per day. For example, if your nerve was injured during spine surgery, the length from the spine to the toes can be 70–80 cm, so full regeneration would take at least 700–800 days! That is 3 years or more.

And during that time the muscle must be stimulated persistently every day! Without this the muscle that lost its motor nerve will atrophy and within roughly two years turn into a gelatinous mass from which there is no return. With stimulation, muscle tissue can be maintained until the nerve grows back to reach the muscle.

An important “ability” of stimulation is the retraining of the neuromuscular (nerve‑muscle) connection. Some studies suggest that the brain and the motor neuron running from the brain to the muscle need at least 10,000 repetitions to relearn how to perform a movement. Retraining non‑functioning muscles after paralysis can be significantly accelerated by stimulation.

I should mention that not every muscle stimulation device is suitable for stimulating muscles affected by peripheral nerve injury, i.e. denervated muscles. It is not worth attempting to treat a paralyzed patient with the cheap few‑thousand HUF devices sold at Lidl, nor with many other less capable units! A device with higher capabilities is needed for this.

While muscles with intact motor innervation can be treated with biphasic square waves, denervated muscles do not respond to that. They can be induced to contract with long‑duration triangular or trapezoidal impulses!

In peripheral paralysis the treatment typically follows a “nice curve”. Treatment usually starts with triangular impulses, then as the nerve regenerates it is gradually switched to trapezoidal, and finally to square impulses.

Stimulation of muscles with healthy innervation

If the nerve running to the muscle is intact (even in stroke it can be intact), there is no need for selective stimulation current. Biphasic square‑wave muscle stimulation is appropriate for these muscles.

A very important difference is impulse duration. For denervated muscle treatment we use 200–900 milliseconds (almost one second), whereas for a healthy muscle we use impulses that are a thousandth of that (microseconds), i.e. much shorter.

There are some conditions in which it is FORBIDDEN!

Selective stimulation current — like other electrotherapy treatments — must not be used in patients with an implanted pacemaker or defibrillator, and is contraindicated in acute thrombosis, tumor, epilepsy, or infectious disease. It should be used with caution during pregnancy and menstruation. You can read detailed contraindications here.

Can selective stimulation current be used at home?

Until 10–15 years ago such devices were available only in hospitals. Their use required a professional who set the waveform, frequency, pulse duration, rise and fall times, current intensity, etc., according to the disease, the type and size of the muscle, and the treatment goal. These settings determine what effect the stimulation will produce.

Today there are selective stimulation current devices available that allow you to perform treatments safely and effectively at home.

Of course, your physiotherapist should tell you which program to use and on which muscles. They should also tell you when you can switch to another type of treatment.

Nevertheless, you can perform the treatment yourself at home safely and effectively. That is what these devices are designed for. Use them confidently!