Can Electrical Stimulation Help Denervated Muscles Recover?
Few muscle recovery and rehabilitation topics can seem as complex and intriguing as the potential for recovering denervated muscles. Understanding whether electrical stimulation can effectively aid in this process is crucial for physiotherapists, medical professionals, and individuals undergoing treatment. This article explores how electrical stimulation offers a positive approach for denervated muscle recovery.
At Anatomical Concepts, we offer a specialist product, the RISE Stimulator, to work with denervated muscle at home or in a clinic. This technology was originally developed and used in a major European multicentre, multi-national research study focused on rescuing denervated and degenerated muscle (the RISE study). The current RISE Stimulator takes advantage of the latest technology and safety features and we now have many clients using the product at home to preserve important aspects of their long-term health.
When discussing the recovery of denervated muscle, we must distinguish between recovering the muscle bulk and tissue quality and restoring the nerve supply. These are different things. We can recover muscle quality in most cases, but recovery of nerve function (re-innervation) is much more variable and depends very much on the cause.
When reinnervation is not expected, the RISE stimulator can prevent muscle mass loss and maintain tissue quality. This can be important for long-term health by reducing the risks of poor circulation and muscle tissue loss, such as pressure sores and other complications. In both situations, it is important to start using electrical stimulation as soon as possible after injury.
Introduction
Denervated muscles have 'lost' their nerve supply and face significant challenges in maintaining function and mass. These muscles can atrophy rapidly, leading to weakness and impaired function. Historically, the prognosis for denervated muscles has been grim, with limited options for effective recovery. For many years, clinicians doubted that anything could be done to benefit these individuals. When I first started to use electrical stimulation in the 1970's, my instructors advised that the electrical energy needed to make such muscles contract was high, and this could put the person at risk of burns. It was also hard to find anyone who advocated this approach clinically because the overall gains were uncertain. You can now be assured that experience worldwide shows the risks to be low and the clinical benefits significant.
Electrical stimulation was first applied to treat denervated muscle over one hundred years ago. In the mid-19th century, the French physician Duchenne de Boulogne used electrical stimulation with denervated muscle. Duchenne, known as the "father of neurology," pioneered electrophysiology and electromyography. He extensively researched electrical stimulation to study muscle function and diagnose neuromuscular disorders. He observed that denervated muscles responded differently to electrical stimulation than healthy muscles. This work laid the foundation for modern electromyography (EMG) development and contributed significantly to our understanding of muscle physiology and the diagnosis of neuromuscular disorders.
Advancements in electrical stimulation technology have improved the situation, as you would expect after all this time. We will briefly explore the science behind denervated muscles, the mechanisms of electrical stimulation, and this therapeutic approach's practical applications and limitations. Let's start with the main causes of denervation.
Causes of muscle denervation
Muscle denervation can result from a number of causes.
Peripheral nerve injury: Damage to the peripheral nerves that innervate the muscles can lead to denervation. This can occur due to trauma, compression, or entrapment of the nerve in a limb for example.
Spinal cord injury: Injury to the spinal cord, especially at the T12 level or below, can disrupt the connection between the motor neurons in the spinal cord and the leg muscles, resulting in denervation. The muscle becomes "disconnected" from the central nervous system.
Neuromuscular disorders: Certain neuromuscular disorders, such as amyotrophic lateral sclerosis (ALS), can cause progressive degeneration of motor neurons, leading to muscle denervation.
Poliomyelitis: The poliovirus can selectively attack and destroy motor neurons in the spinal cord, causing muscle denervation and paralysis.
Guillain-Barré syndrome: This autoimmune disorder can attack the peripheral nerves, leading to muscle weakness and denervation.
Diabetic peripheral neuropathy: Uncontrolled diabetes can cause damage to peripheral nerves, including those that innervate muscles, leading to denervation.
Radiation therapy: High-dose radiation therapy used to treat certain cancers can cause damage to peripheral nerves, potentially leading to muscle denervation.
At Anatomical Concepts, we commonly work with persons who have experienced a complete or incomplete spinal cord injury at a low level on the spine (T12 or lower), affecting the so-called lower motor neurons. We also see individuals with Brachial Plexus injuries affecting an arm or shoulder.
Understanding Denervated Muscles
What Happens to Muscles When They Are Denervated?
Muscles left untreated transform over time to a mass of tissue incapable of behaving like muscle
When a muscle becomes denervated, it loses its connection to the nervous system. This disconnection disrupts the signalling pathways necessary for muscle contraction and maintenance. Without regular neural input, the muscle fibres begin to deteriorate. This process, known as atrophy, can occur rapidly and result in significant muscle wasting. Denervated muscles also experience changes in their biochemical environment, further complicating the recovery process. Eventually, denervated muscle tissue is replaced with collagen and fat and cannot contract. If this process is advanced, it cannot be reversed. This is why electrical stimulation is best started early. Electrical stimulation for denervated muscle relies on the structure of the muscle fibres remaining largely intact even though the nerve is damaged. Let's expand on this point.
Factors That Determine the Potential for Recovery
The potential for recovery in denervated muscles depends on several factors. The duration of denervation plays a critical role; the longer a muscle remains denervated, the more challenging it becomes to restore function. As we will learn below, effective electrical stimulation relies on making muscle fibres contract directly. This cannot work if only a few muscle fibres remain in the muscle; it becomes incapable of contracting. If many years have passed since an injury, we would still suggest trying electrical stimulation because the risks are low. However, the chance of success is much greater within one to two years after an injury.
Additionally, the extent of nerve damage and the presence of any underlying medical conditions can influence recovery outcomes. Age is another factor, as younger patients typically have a better capacity for regeneration. Understanding these variables is essential for developing effective treatment plans.
How Electrical Stimulation Works
Overview of Electrical Stimulation and Its Different Modalities
We most often apply electrical energy to the body through the skin when using electrical stimulation. Although, for some applications, the energy source is implanted in the body, I'm restricting the discussion to the most common situation in rehabilitation, when electrodes are placed on the skin surface over the muscles of interest. The penetrating energy will invoke physiological effects such as stimulating nearby sensory and motor nerves. The result of all of this, we hope, will be therapeutic effects.
Such electrical stimulation frequently involves using controlled electrical impulses to induce muscle contractions. Various modalities exist, each with unique characteristics and applications. Neuromuscular electrical stimulation (NMES), for example, is commonly used in rehabilitation settings and targets intact motor nerves. Physiotherapists commonly use it to produce functional contractions in muscles with intact nerves. However, NMES will not produce a contraction in a denervated muscle.
Units like the RISE Stimulator produce a stimulation energy that does not rely on an intact nerve. Instead, the energy produced acts directly on the muscle fibres to produce a useful contraction.
Both for NMES and for denervated muscle, the electrical energy will typically be in what is referred to as a biphasic rectangular pulse form. However, with NMES, the width of the pulses is likely to be less than 1 ms with waveform frequencies up to 50 Hz and with denervated muscles, we may be working with pulse widths of 120 - 200 ms and low-frequency waveforms of less than 2 Hz.
Comparing stimulation parameters for NMES and denervated muscle
Mechanisms by Which Electrical Stimulation Aids in Muscle Recovery
The primary mechanism by which electrical stimulation aids in muscle recovery is through the promotion of muscle contractions. These contractions help maintain muscle mass and prevent atrophy. Additionally, electrical stimulation can improve blood flow to the affected area, enhancing nutrient delivery and waste removal. This process promotes a more favourable environment for muscle recovery. Furthermore, electrical stimulation may facilitate the reorganisation of neural pathways, potentially aiding in restoring muscle function.
Research and Evidence
Recent Studies on the Effectiveness of Electrical Stimulation for Denervated Muscles
Recent studies have shown promising results regarding the use of electrical stimulation for denervated muscle recovery. At the end of this article we have provided some references to the scientific literature.
Practical Applications
Guidelines for Using Electrical Stimulation in Clinical Settings
For physiotherapists and medical professionals, implementing electrical stimulation in clinical settings requires careful consideration. It is crucial to thoroughly assess the patient's condition and tailor the treatment plan accordingly. Whilst electrical stimulation is, in general, a safe therapy, there are always contraindications, and the manufacturer's guidance should always be followed. With denervated muscle, the current levels may be higher than those typically found in NMES applications, so it is important to follow the manufacturers guidelines.
Parameters such as the intensity and frequency of electrical impulses should be adjusted based on the patient's tolerance and response. Regular monitoring and adjustments are essential to maximize the therapeutic benefits.
Home-Based Electrical Stimulation for Muscle Recovery
Home-based electrical stimulation offers a convenient option for patients to continue their treatment outside of clinical settings. Portable electrical stimulation devices such as the RISE Stimulator allow patients to manage their therapy independently. However, proper training and guidance is essential to ensure safe and effective use. Patients should also be encouraged to maintain regular follow-ups with their healthcare providers to track progress and make any necessary adjustments.
Limitations and Future Directions
Discussion of the Current Limitations in the Use of Electrical Stimulation
Despite its potential, electrical stimulation has its limitations. One significant challenge is ensuring consistent and effective muscle contractions, particularly in severely denervated muscles. Additionally, the cost of electrical stimulation devices and ongoing therapy sessions can be a barrier for some patients. More extensive research is needed to establish standardised protocols and optimize treatment parameters.
Exploration of Potential Future Developments in This Field
The future of electrical stimulation in muscle recovery holds exciting possibilities. Advances in technology may lead to more sophisticated and user-friendly devices. Researchers are also exploring the combination of electrical stimulation with other therapies, such as regenerative medicine and stem cell therapy, to enhance recovery outcomes. Continued collaboration between researchers, clinicians, and engineers will drive innovation and improve the effectiveness of electrical stimulation for denervated muscles.
Conclusion
Electrical stimulation offers a promising avenue for the recovery of denervated muscles. By understanding the mechanisms behind muscle denervation and the benefits of electrical stimulation, medical professionals and patients can make informed decisions about incorporating this therapy into their treatment plans. While challenges remain, ongoing research and technological advancements pave the way for more effective and accessible solutions. For those looking to explore the potential of electrical stimulation further, engaging with experts and staying informed about the latest developments is key. Together, we can unlock new possibilities in muscle recovery and rehabilitation.
Research Literature
Kern, H, et al. (2004), ‘Long-term denervation in humans causes degeneration of both contractile and excitation-contraction coupling apparatus, which is reversible by functional electrical stimulation (FES): a role for myofiber regeneration’, J Neuropathol Exp Neurol, 63 (9), 919–31.
Kern, H, et al. (2005), ‘Muscle biopsies show that FES of denervated muscles reverses human muscle degeneration from permanent spinal motoneuron lesion.’, J Rehabil Res Dev, 42 (3 Suppl 1), 43–53.
Kern, H, et al. (2005), ‘Recovery of long-term denervated human muscles induced by electrical stimulation.’, Muscle Nerve, 31 (1), 98–101.
Kern, H, et al. (2006), ‘Functional electrical stimulation of denervated muscle: Clinical improvements’. Basic Appl Myol 16 (3&4): 97–99, 2006
Kern, H, et al. (2008), ‘Stable muscle atrophy in long-term paraplegics with complete upper motor neuron lesion from 3- to 20-year SCI.’, Spinal Cord, 46 (4), 293–304.
Kern, H, et al. (2009), ‘European Project RISE: Partners, protocols, demography’. Basic Applied Myology 19 (5&6): 211–216, 2009
Page 3 of 6 Kern, H, et al. (2010), ‘One year of home-based daily FES in complete lower motor neuron paraplegia: recovery of tetanic contractility drives the structural improvements of denervated muscle.’, Neurol Res, 32 (1), 5–12.
Kern, H et al. (2010) ‘Home-Based Functional Electrical Stimulation Rescues Permanently Denervated Muscles in Paraplegic Patients With Complete Lower Motor Neuron Lesion’, Neurorehabil Neural Repair OnlineFirst, published on May 11, 2010 as doi:10.1177/1545968310366129
Kern, H et al (2010), ‘Permanent LMN denervation of human skeletal muscle and recovery by h-b FES: management and monitoring’ European Journal Translational Myology – Myology Reviews 2010; 1 (3): 91–104
Kern, H (2014), ‘Funktionelle Elektrostimulation Paraplegischer Patienten.’, Eur J Transl Myol, 24 (2), 2940.
Kern, H and U Carraro (2014), ‘Home-Based Functional Electrical Stimulation for Long-Term Denervated Human Muscle: History, Basics, Results and Perspectives of the Vienna Rehabilitation Strategy.’, Eur J Transl Myol, 24 (1), 3296.
Kern, H, et al. (2017), ‘Atrophy, ultra-structural disorders, severe atrophy and degeneration of denervated human muscle in SCI and Aging. Implications for their recovery by Functional Electrical Stimulation, updated 2017.’, Neurol Res, 39 (7), 660–66.
Kern, H, et al. (2018), ‘To Reverse Atrophy of Human Muscles in Complete SCI Lower Motor Neuron Denervation by Home-Based Functional Electrical Stimulation.’, Adv Exp Med Biol, 1088 585–91.
Kern, H and U Carraro (2020), ‘Home-Based Functional Electrical Stimulation of Human Permanent Denervated Muscles: A Narrative Review on Diagnostics, Managements, Results and Byproducts Revisited 2020.’, Diagnostics (Basel), 10 (8), 529.
A Few of our Related Articles on Denervation
Why your NMES product probably doesn't work with denervated muscle.
Lower Motor Neuron Lesion versus Upper Motor Lesion
https://www.anatomicalconcepts.com/articles/lower-motor-neuron-lesion-versus-upper-motor-lesion
FES and Peripheral Nerve Injuries: Exploring Benefits of Functional Electrical Stimulation
https://www.anatomicalconcepts.com/articles/fes-and-peripheral-nerve-injuries
Denervated muscle rehabilitation with the RISE Stimulator
https://www.anatomicalconcepts.com/articles/how-to-use-the-rise-s