Electrical stimulation can condition muscles or help with pain. How do the techniques differ?
Electrical stimulation is a widely used method of applying energy to the body to produce a physiological response. By controlling the nature of this energy, we can expect to produce a useful therapeutic effect. These ideas have decades of practical use and are generally safe and effective in many situations. Still, it can be difficult to understand how to match one of the many techniques to a particular clinical case.
At Anatomical Concepts, we have expertise in using electrical stimulation in many therapy applications. For example, we have clients with a neurological condition such as a spinal cord injury or stroke that use FES cycling at home for long-term health. We will explain this a bit later. We also use forms of electrical stimulation combined with therapy exercises to help weak muscles get stronger, help heal chronic pressure ulcers, compensate for injured nerves or, as this article's title suggests, help manage acute or chronic pain. To do these various things, the energy "prescription" must vary. We often need different products to accomplish these things. In this article, we look at electrical stimulation and how it is fine-tuned to suit these various therapy situations.
Some fundamental points
As we mentioned, electrical stimulation applied to the body for therapeutic effect has existed for over a hundred years. Of course, our understanding of the principles and the technology to control it has greatly improved. In the distant past, electrical stimulation was, at times, the territory of charlatans, which took some time to shake off. Many forms of stimulation have arisen during this time. Some are unique to particular countries; unfortunately, no internationally agreed-upon terminology exists. This means it can be difficult to explore the literature, as sometimes the same techniques are given various names depending on the source.
Often, you will see the term Functional Electrical Stimulation (FES) being used broadly to describe applications in which the stimulation has a "functional purpose". The term NMES (Neuromuscular electrical stimulation) is often seen in recent times and reflects the fact that in many therapy applications, the aim is to stimulate the nervous system and, by this means, induce a muscle contraction.
TENS (for Transcutaneous Electrical Nerve Stimulation) is frequently associated with stimulation for pain relief. However, most forms of stimulation we use in rehabilitation are transcutaneous, too, because they involve methods in which electrical energy is applied to the skin from where it penetrates the deeper tissues and activates the nervous system structures that make a muscle contract.
Perhaps the fundamental division is whether the intention is to use the stimulation in therapy at a functional level or whether the intent is primarily to operate at a physiological level. Thomas Schick describes a structure that makes sense in his article in the recent book. (See Reference Below)
In this article, we will adhere to the title, which aims to examine the techniques of conditioning muscles versus those for relieving pain. We will first consider how stimulation is applied to the body, and then the stimulation parameters (the "prescription") used to generate the therapy effect.
Indications and contraindications
Indications and contraindications are important considerations when using electrical stimulation in therapy. Indications refer to specific conditions or situations where electrical stimulation may be beneficial, whilst contraindications refer to situations where it should not be used or only used with caution. These days, we can go online and find many electrical stimulation devices that are on open sale. We advise using only electrical stimulation devices classified as medical devices for therapy situations. Although medical devices will tend to be more expensive than those produced for more general use, it ensures that the product has been designed and manufactured to ensure a high level of safety in use. Every medical device will list the indications and contraindications in the user manual, which should be followed carefully. Some contraindications may be described as "absolute" and some as "relative" based on the anticipated form of risk.
Applying stimulation to the body
Whilst electrical stimulation can be delivered via implanted devices we will restrict our discussion to the more usual external devices used in rehabilitation. Electrodes are a critical component in delivering such electrical stimulation to the body. They serve as the interface between the stimulation device and the patient's skin, ensuring the effective transfer of electrical energy. The skin and surface tissues represent a barrier to the penetration of the energy. Generally, electrodes are composed of conductive materials that allow electric currents to pass through them efficiently. They are designed to be adhesive, maintaining stable contact with the skin during therapy sessions. For many applications, a pair of electrodes are placed some distance apart on the limb being treated. Placement does vary depending on whether we are trying to make a muscle contract or deal with pain.
electrodes allow the energy to penetrate the skin and deeper tissues
When an electrical current is passed through the electrodes, it penetrates the skin and reaches the underlying muscles and nerves. Both sensory and motor nerves are affected and the result produced depends on the specific type of energy being delivered - the stimulation parameters at work. Generally, the energy will be lower if we are dealing with pain and higher if we expect to produce a muscle contraction. We will get into more detail on the stimulation parameters shortly, but for now, imagine that as we increase the level of energy applied to the body, we will first activate the sensory nerves and then the motor nerves.
The effectiveness of the stimulation also hinges on the quality of the electrodes. Over time, the adhesive properties and conductivity can deteriorate, necessitating regular checks and replacements to maintain optimal performance. Additionally, good skin preparation, such as cleaning the skin to remove oils and dirt, can enhance electrode adhesion and conductivity. In sum, the functionality and placement of electrodes are paramount for ensuring that electrical stimulation therapy is both effective and safe.
The RISE Stimulator - we use large electrodes to cover as much tissue as possible
In the special case of working with denervated muscle, we use the specialist RISE Stimulator. This uses a different form of electrode pair. When a muscle becomes denervated, we can't rely on the motor nerves to make the muscles contract, and the stimulation parameters are set to work directly with the muscle fibres. The higher energy level required means that gelled electrodes should not be used. The electrodes we commonly use for denervated muscle consist of a wet sponge and carbon rubber combination. These allow greater energy levels to be used without risking skin irritation or burns.
Stimulation parameters - the prescription
If we were able to visualise the energy patterns of electrical stimulation in available products, we might see that a wide variety of waveforms are being used across the spectrum of applications. The common way of looking at these waveforms is via their time series. For example, biphasic rectangular pulses are commonly used in electrical stimulation therapy, but there isn't a single pattern of energy that dominates across all applications. Biphasic waveforms, in general, appear to be both very popular and widely used. At Anatomical Concepts we use biphasic forms across pretty much all out therapy applications. Here's a summary of the key points:
Biphasic waveforms have several advantages:
A common biphasic pulse pattern
Biphasic waveforms are charge-balanced, making them safer for clinical use by avoiding toxic charge accumulation associated with direct current stimulation.
They are less likely to cause skin reactions and are generally more comfortable for patients.
There are different types of biphasic waveforms:
Symmetrical biphasic waveforms: These use identical positive and negative phases that cancel each other out, producing a zero-net charge.
Asymmetrical biphasic waveforms: These have different positive and negative phases.
Biphasic monopolar (BPMP) and biphasic bipolar (BPBP) waveforms are also used, with different characteristics.
Other common waveforms include,
Interferential Current (IFC): Used for pain management and offers deep tissue penetration, Premodulated Current (Premod),
Microcurrent: Uses micro-size, pulsating current.
The waveform selection may depend on factors like the depth of penetration needed, the type of tissue being targeted, and the therapeutic goal (e.g., pain relief, muscle strengthening, or nerve stimulation).
Clinicians and researchers continue to study and compare different waveforms to optimize treatment outcomes for various conditions.
To describe a waveform, we often use three simulation parameters
Frequency: How often stimulation pulses repeat
Pulse width: The width of each pulse. Typically, microseconds or milliseconds, depending on the application.
Current/voltage: The height of each pulse.
In addition, for some applications, pulses will be delivered in bursts with rest periods between the bursts.
Our applications
FES cycling
Functional Electrical Stimulation (FES) Cycling is a specialised application that leverages electrical stimulation to induce muscle contractions, enabling individuals with neuromuscular impairments to perform cycling exercises. This technology is particularly beneficial for patients with conditions such as spinal cord injuries, multiple sclerosis, stroke, or other forms of paralysis. By stimulating specific weak or paralysed muscle groups in a coordinated manner, FES Cycling facilitates the movement of the legs in a cycling motion, allowing individuals to engage in exercise that would otherwise be impossible due to their condition.
FES Cycling involves placing electrodes on the skin over the muscles responsible for cycling movement, namely the quadriceps, hamstrings, and gluteal muscles. The lower leg muscles can also be included. Some versions of our bikes also allow upper limb exercise using the arm and shoulder muscles.
A programmable stimulator sends electrical pulses through these electrodes in sync with the movement of the bike pedals, causing the muscles to contract in a sequence that mimics natural cycling. The intensity and timing of these pulses are carefully controlled to ensure smooth, rhythmic motions and to optimise the therapeutic benefits.
FES Cycling offers several significant advantages, including muscle strengthening, improved cardiovascular health, and prevention of muscle atrophy. Additionally, the rhythmic and repetitive nature of cycling can enhance circulation and aid in the reduction of spasticity. For many users, it also provides psychological benefits by promoting independence and enhancing their quality of life. We tailor the settings to the individual's needs and monitor progress over time.
Pain applications
Pain applications are fairly common, and sometimes, a client's pain needs are primary and must be addressed before other functional applications can be tackled. As most people appreciate, pain can be very challenging to manage, and there is no such thing as a "single" solution. We find, particularly with chronic pain that some exploration is needed to find an effective approach. However, if it works, electrical stimulation can be a very desirable therapy for pain as it has few potential side effects and is low-risk.
Understanding the different types of pain is essential for effective management and treatment. Pain can broadly be categorised into two primary types: nociceptive and neuropathic.
Nociceptive Pain is the most common type in the general population and arises from actual or potential tissue damage. It can be classified further into somatic and visceral pain:
Somatic pain originates from the skin, muscles, bones, or joints and is usually well-localised. An example would be a sprained ankle or a cut.
Visceral pain stems from the internal organs and is often diffuse and difficult to pinpoint, such as pain experienced during a heart attack or gastrointestinal issues.
Neuropathic Pain is sometimes experienced by our clients following a spinal cord injury and results from damage or dysfunction in the nervous system itself. It is often described as burning, shooting, or electric-shock-like pain. Conditions such as diabetes, multiple sclerosis, or sciatic nerve pain also fall under this category.
Each type of pain requires a tailored treatment approach. Understanding pain's underlying mechanisms and characteristics is crucial to formulating a personalised and effective pain management plan.
In our product portfolio, we typically use the Stimulette Edition 5 for pain applications. This is because it features several effective approaches to pain relief. The table below shows the abbreviations for these approaches as well as their strengths and weaknesses.
A variety of apporaches to pain featured in the Stimulette Edition 5
RISE Stimulator for denervated muscle
The RISE Stimulator represents a cutting-edge technology specifically designed to rehabilitate denervated muscles. Denervated muscles, which have lost their connection to the central nervous system due to nerve damage, present unique challenges in rehabilitation. Traditional electrical stimulation methods are often ineffective for these muscles, necessitating specialised approaches like those provided by the RISE Stimulator.
The RISE Stimulator utilises customised waveforms capable of penetrating deeper into muscle tissue, directly stimulating the muscle fibres. This technology helps promote muscle contraction even in the absence of neural input. The following features illustrate how the RISE Stimulator optimally aids in the recovery of denervated muscles:
High-Intensity Stimulus: The RISE Stimulator delivers high-intensity electrical pulses designed to elicit strong muscle contractions. This is crucial for maintaining muscle mass and preventing atrophy in denervated muscles.
Variable Pulse Duration: The device adjusts the pulse width to cater to the specific requirements of denervated muscle tissue, ensuring effective and targeted stimulation. Pulse widths can be 200 milliseconds compared with the microsecond during typically of neuromuscular stimulation applications.
Sequenced Contractions: Pulse are delivered in bursts to help combat fatigue and we use well researched stimulation patterns to normalise and then strengthen the affected muscles
Adaptive Settings: The RISE Stimulator offers adaptive settings that are customised to the patient's condition and progress, allowing for continuous therapy optimisation. When reinnervation is expected, the stimulation can support rapid recovery. When denervation is complete this approach fosters the best long term health.
Clinical protocols for using the RISE Stimulator involve comprehensive assessments to identify the extent of nerve damage and the degree of muscle denervation. Once these factors are understood, a tailored treatment plan is developed, focusing on gradually increasing the intensity and duration of stimulation to improve muscle strength and functionality over time. This personalised approach ensures that patients receive the most effective treatment to support their rehabilitation journey.
Summary and Conclusion
It might seem amazing that electrical stimulation can support a vast range of applications. However, we must first understand that "electrical stimulation" is not one thing. Particular applications require specific technology, stimulation parameters and protocols.
We briefly discussed methodologies and technologies that offer significant advancements in rehabilitation and pain management. FES Cycling therapy provides robust benefits, such as muscle strengthening, cardiovascular improvement, and psychological enhancements, tailored to individual needs and carefully monitored over time. Pain applications are approached with a thorough understanding of nociceptive and neuropathic pain, with tools like the Stimulette Edition 5 offering multiple effective solutions for pain relief while maintaining low risk and few side effects.
The RISE Stimulator stands out as a cutting-edge innovation for rehabilitating denervated muscles, addressing unique rehabilitation challenges by delivering high-intensity stimuli and customised waveforms. Its adaptive settings and sequenced contractions support muscle contraction and prevent atrophy, even in the absence of neural input. Clinical protocols ensure that assessments and tailored treatment plans are in place for optimal patient outcomes.
In conclusion, these advanced strategies and technologies provide a comprehensive framework for effective pain management and muscle rehabilitation.
Reference
“Functional Electrical Stimulation in Neurorehabilitation - Synergy effects of technology and therapy” Edited by Thomas Schick. Springer. 2022
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