The term “selective current stimulation” is a term you hear from doctors and physiotherapists. It is a form of muscle stimulation (EMS) treatment used to address muscles with damaged (denervated) motor nerves, resulting in the absence or partial loss of voluntary muscle movement (peripheral paralysis). Selective stimulation current only stimulates and causes contraction of the muscle in such a diseased muscle (hence the name selective). Let’s look at the essentials of this topic.
What is selective current stimulation treatment?
Selective electrical stimulation is a form of electrotherapy. It can treat denervated muscles, which are muscles that have lost their motor nerve connections.
Several forms of peripheral paralysis cause this type of paralysis: peroneal paralysis, facial nerve paralysis, spinal hernia, nerve injury after spinal fracture, nerve injury during spinal surgery, etc.
Watch out! Some therapists also mistakenly treat paralysis due to stroke with selective stimulation. However, selective stimulation is not good for the stroke patient because it causes an increase in muscle stiffness (in jargon: increases spasticity). The motor nerve of the muscle affected by stroke is healthy (the problem is at the brain junction). Hence, stroke-related paralysis should be treated with “smooth” biphasic square wave muscle stimulation (at low frequency) rather than selective stimulation.
Selective stimulation is selective in that it acts on the denervated (lower motor neuron damaged) muscles! The denervated impulse is too long to treat healthy muscles. Selective stimulation of healthy muscle is unpleasant, even painful, and has little effect.
Selective electrical stimulation involves applying a milliampere (mA) electrical pulse through an electrode (which can be self-adhesive, metal or rubber) to the skin and causing the muscle to contract. The shape of the pulse can be triangular, trapezoidal or square wave. The frequency, intensity and duration of the contraction can be controlled to determine how much the contraction grips the muscle bundle, at what speed and at what frequency.
You can focus the treatment on a specific muscle or muscle group, limiting its effect to those areas.
“Normally” muscle contraction is caused by an electrical signal from your brain. During the stimulation current treatment, the muscle receives similar artificial impulses.
In both cases, it contracts by exactly the same mechanism, the same metabolic processes take place in it, and it tires in exactly the same way.
Treatment of a muscle that has lost its motor nerve
This is the application of selective stimulation current. Treating a denervated muscle with selective stimulation current on a daily basis enhances the likelihood of its recovery.
Those who do not receive regular stimulation in current treatment improve little or significantly more slowly. With stimulation, there is a real chance of regeneration and “re-growth” of the nerves.
You need to know that nerve pathways regenerate extremely slowly. Even under optimal conditions of continuous stimulation, they grow at a maximum of 1 mm per day. If you have a nerve injury during a spinal operation, for example, the nerve can grow from the spine to the toes by 70-80 cm, which means that it takes at least 7-800 days to fully regenerate. And in the meantime, you need to stimulate it every day. Without it, the muscle that has lost its motor nerve will atrophy, and in about two years it will turn into a gelatinous mass from which there is no return. Stimulation can keep the muscle tissue alive until the nerve reaches the muscle again.
Stimulation has the very important “ability” to “retrain” the neuromuscular (nerve-muscle) connection. According to some studies, the brain and the motor neurons that run from the brain to the muscles need at least 10,000 (ten thousand) repetitions to relearn how to perform a movement. Stimulation can significantly expedite the process of relearning muscles that have become nonfunctional after paralysis.
Specific devices for denervated muscle treatment
I should mention here that not all muscle stimulator devices are suitable for stimulating a peripheral nerve injury or, in other technical terms, a denervated (lost its innervation) muscle. You can treat a healthy muscle with a motor nerve using a biphasic square wave, but a denervated muscle does not respond to this type of stimulation. Instead, you can make it contract with a long-duration pulse, known as a triangular or trapezoidal pulse. Treatment for peripheral paralysis has a “nice arc”. They usually start with a triangular pulse, then as the nerve renegades, they slowly move to a trapezoidal pulse and finally to a square pulse.
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- All phases in the treatment of peroneal palsy
- Stimulation of denervated muscles in general
- Stimulation of muscles with intact nervous control – either biphasic or monophasic EMS
- Pain therapy (TENS) with biphasic or monophasic pulses
Stimulation of muscles with healthy innervation
If the nerve fiber running to the muscle is preserved (even in the case of a stroke), there is no requirement for selective stimulus current. A biphasic square wave for muscle stimulation is suitable for this purpose.
An important difference is also the pulse duration. In treating denervated muscle, a pulse duration of 200-900 milliseconds (almost a second) is employed, whereas for healthy muscle, a much shorter pulse duration of a thousandth of a second (microsecond) is utilized.
Conditions that strictly prohibit its use
People should not use selective stimulation current -nor any other electrotherapy treatment- in the case of an implanted pacemaker or defibrillator, acute thrombosis, tumour, epilepsy, or infectious disease. They should exercise caution when using it during pregnancy and menstruation. Read more about contraindications here.
Is it possible to use selective stimulation current therapy at home?
A mere 10-15 years ago, such devices were only available in hospitals. To use them, you needed a specialist who could adjust the waveform, frequency, pulse duration, rise and fall times, current intensity, etc. according to the type and size of the disease and muscle, and the treatment goal.
Today, selective stimulation current devices are available that you can use in your home to perform the treatment yourself.
Of course, which program to use and on which muscles are up to your physiotherapist. Also when you can switch to another type of treatment.