"It's the most powerful weapon we can use to change the world"
Muscle electrical stimulation is a therapy that is used to enable a person to flex a muscle. For people who need therapy for muscle strengthening, this method can be used because the muscle can be flexed without the person being able to do so on their own. This may be because the muscle is weak or paralyzed. Sticky pads are placed on the skin over the target muscle. This enables a controlled electrical current from a small device to safely make the muscle flex. The timing of the electrical current can be programmed on the device to help someone use a muscle when moving. A great example of this is flexing the muscles on the front of the leg to lift up the toes when walking.
How does electrical stimulation work on muscles?
The controlled electrical current applied through the sticky pads from the device tries to copy what happens when the brain tells a muscle to flex or contract. When our brain tells a muscle to contract, it sends an electrical current that travels through the nerves in our body. This sets off a series of chemical reactions at the place where the nerve meets the muscle. Muscle electrical stimulation does this as well but instead of the brain sending the electrical current through the body, a device is used to send the electrical current directly to the muscle.
Why does it work?
Muscle electrical stimulation works when the nerve is properly connected to the muscle. This means that the signal is working well so all it needs is an electrical current to enable the muscle to flex or contract. Muscle electrical stimulation works because the person doesn’t need to be able to flex or contract it themselves, the device can do it for them. This can then teach the pattern and habit of how the person can learn to use the muscle themselves.
Transcutaneous electrical nerve stimulation (TENS) is the most common type of electrical therapy using a small, battery-operated device which sends a low-voltage electrical current through the skin. It is usually used to help with pain management. Sticky pads or electrodes are placed in the area where pain is being experienced. The electrical current stimulates the nerves in the affected area and sends signals to the brain that distort normal pain signals.
Neuromuscular electrical stimulation (NMES) is mainly used for muscle strengthening in children with cerebral palsy. NMES closely mimics strength training in that muscles are activated or stimulated at pre set on and off times. As an example, the muscle may be stimulated to contract for 5 seconds but then have 10 seconds of rest. In the same way as TENS, it also involves the use of a device (usually battery operated) that sends electrical impulses via electrodes to activate the targeted muscles. The mechanism for improving strength is based on the overload principle by increasing the size of the muscle (known as the cross-sectional area) and improving how efficiently a muscle contracts (also known as synaptic efficiency).
The combination of Neuromuscular Electrical Stimulation and a specific activity (we often call it a task specific activity) is referred to as Functional Electrical Stimulation (FES). In this instance, the sticky electrode pads are placed on the target muscles and are timed to flex or contract during a very specific movement. An example of this is using the electrical current to stimulate the muscles at the front of the leg to lift the toes up. If this movement is done with a person sitting on a chair, it is simply referred to as NMES. However if the same thing is done but the electrical current is timed so that it lifts the toes up with each step whilst the person is walking, it is known as Functional Electrical Stimulation. This is important for the person because the muscles that are needed to lift the toes up when walking are weak and this can cause tripping or falling when walking. However, if the device is used to help the person do this, it can greatly improve how a person moves at home, school and community.
Research has shown that Functional Electrical Stimulation in children with cerebral palsy where one side of the body is affected can
- Improve ankle movement
- Improve muscle strength
- Increase the size of the muscle
- Improve the walking pattern (even after the device has been taken off).
Frequency refers to the number of electrical impulses that are delivered to the muscle each second. The higher the frequency the greater the muscle force that can be generated. However, this also means that the muscle will fatigue quicker too. Human muscles fire at low frequencies, typically between 10-30Hz. However when using muscle electrical stimulation, the only way to get the muscle to flex and contract with enough movement and strength, higher frequencies are needed. This is typically around 33-50 Hz.
Pulse width refers to how long each electrical impulse is. This is measured in microseconds. The choice in how long each impulse is depends on how a person can tolerate it, the type of muscle it is, the activity that is being performed and the size of the muscle. Typically, a pulse width between 200-250us (microseconds) is used in neurorehabilitation. Longer duration pulses proportionally increase the amount of electrical power being supplied to assist with the muscle contraction. When stimulating smaller muscles such as the muscle that lifts the toes up when walking, short duration pulses (such as 50us) tend to be more comfortable.
Amplitude refers to the intensity of the current. This is measured in milli-Amps. Intensity must be high enough to cause a muscle contraction but not necessarily a maximal contraction. The intensity required to achieve the desired contraction will vary from person to person depending on individual sensation, skin resistance, size of muscle and the size and type of electrodes. This is generally that last parameter to be adjusted and is fully dependent on how the child is able to tolerate the sensation.
Cerebral palsy is the most common cause of physical disability in children and is an umbrella term that is used to describe a group of motor dysfunctions caused by non-progressive damage to the developing brain. Non-motor disturbances of sensation, perception, cognition and communication are also usually present and can influence the ability to perform tasks of daily living. Cerebral palsy affects body movement, muscle control, muscle coordination, muscle tone, reflex, posture and balance. It can also impact fine motor skills, gross motor skills and oral motor functioning. The type of movement dysfunction, the location and number of limbs involved, as well as the extent of the impairment, varies from one individual to another.
Types of CP
CP is most commonly described as either unilateral or bilateral. Unilateral refers to one side of the body (including upper limb, lower limb and trunk) that is more affected. Bilateral refers to both sides of the body being affected. This can be both the legs as well as the arms. Other descriptions of CP include spasticity, dyskinetic, ataxic and mixed presentation.
The Gross Motor Function Classification System or GMFCS provides a description of how children with cerebral palsy moves on a day to day basis. The levels go from 1 (able to walk independently without equipment in most settings) through to 5 (dependent on equipment and physical support in most settings). The classification system helps clinicians to communicate with each other succinctly whilst still being descriptive. It also helps to provide a common language to co-ordinate and provide treatments.
How does CP affect movement?
Cerebral Palsy affects a child’s movement and co-ordination. Muscles can be weak and small in size and this can also affect how a person with cerebral palsy moves. The reason for this is that when a muscle is small and weak, it will have a harder time producing enough force for some movements such as walking. The child may walk unevenly and look like they are walking with a bit of a limp. This can mean the child is more likely to trip and fall when walking.
How does MES work on CP?
MES has been used as an alternative option for children who have problems with walking. MES has the potential to improve a number of different areas including muscle size and strength, spasticity, range of motion, walking speed, positioning of the foot and the way that the ankle moves. Research shows that this method is safe and well tolerated even in young children.
What's the Next Step? If you'd like to know more, please contact the Next Steps Team and visit our blog section for all the latest information!