Denervated Muscle Stimulation: Why Optimal Intensity Beats Maximum Intensity
When treating denervated muscles with electrical stimulation, a common assumption is that stronger is better—that maximum current intensity will produce the best results. However, clinical evidence tells a different story: optimal outcomes come from finding the minimum effective intensity, not the maximum tolerable one.
I generally advise clients at the beginning not to worry too much about the specific current level, but to increase the current intensity until they start to see a contraction, and then increase by about 10% over that. I would call that the minimum effective intensity.
Understanding Denervated Muscle Requirements
As we discussed in our seminar series, in our Vimeo channel, and in a number of articles on this website, denervated muscles require a fundamentally different stimulation approach than healthy, innervated muscles. Without nerve connections, muscle fibers must be stimulated directly, which often demands significantly higher stimulation intensities—current delivery possibilites are up to 250 mA compared to the much lower levels used for standard neuromuscular electrical stimulation. At the same time, although the waveform shape (typically biphasic rectangular pulses) is similar to those used in neuromuscular electrical stimulation, the pulse widths are much greater and can often be 200 milliseconds or more. It's rare for neuromuscular electrical stimulator units to offer pulse widths of close to 1 ms. These long pulse widths combined with relatively high currents mean that the overall intensity of stimulation is something to pay attention to.
The RISE stimulator is specifically designed to deliver these higher intensities safely and effectively, with parameters optimised for denervated muscle rehabilitation. However, all that available power needs to be directed appropriately and safely.
Why More Current Isn't Always Better
While adequate current is essential to achieve muscle fibre contraction, excessive intensity creates several problems that can actually impede recovery:
Risk of Tissue Damage
High current densities can cause electrochemical burns at the electrode-tissue interface, resulting from pH changes during prolonged stimulation. These burns compromise skin integrity and can interrupt treatment protocols—the opposite of the intended outcome. Most commercial stimulators are limited - 130 to 150 mA specifically because of burn risks at higher intensities.
Muscle Fibre Damage
Research shows that excessive electrical stimulation intensity can induce muscle fibre damage similar to that caused by maximal eccentric contractions. This damage manifests as histological alterations, elevated creatine kinase levels, and delayed onset muscle soreness—all counterproductive when the goal is muscle preservation and recovery.
Reduced Treatment Compliance
Denervated muscle rehabilitation requires consistent, long-term stimulation protocols with hundreds of contractions per session. If current intensity creates significant discomfort or tissue irritation, users may reduce treatment frequency or duration, undermining the cumulative benefits that come from sustained therapy over weeks and months.
The Minimum Effective Intensity Principle
The optimal approach focuses on achieving visible, functional muscle contractions with the lowest current intensity necessary. This principle balances effectiveness with safety and tolerability.
Clinical studies support this moderate-intensity approach. Research demonstrates that patients can achieve significant improvements in muscle thickness and pennation angle using currents of 20-50 mA over 12 weeks. Other studies show that denervated quadriceps muscles can produce torque levels of 16-38 Nm—sufficient for functional activities like standing—without requiring maximum current settings.
Importantly, the number of contractions appears more critical than contraction intensity for preserving muscle mass and function. This means consistent, moderate-intensity stimulation over time may be more beneficial than infrequent maximum-intensity sessions.
Recommended Stimulation Parameters with the RISE
Based on current evidence and clinical experience, effective denervated muscle stimulation should use What we would call a twitch contraction protocol at the beginning. Over time, a tetanic contraction protocol is introduced. Twitch contraction protocol will typically use biphasic rectangular pulses of up to 200 milliseconds. These pulses are delivered in bursts with rest periods between the bursts, and the Twitch Contraction Protocol is a low-frequency one of less than 2 Hz. As the name suggests, the tetanic stimulation protocol produces a stronger, sustained contraction. It may use the same waveform shape. It will use shorter pulse widths and higher frequencies.
We typically suggest 30 minutes of stimulation exercise per muscle group, for 5 to 6 days per week. You consider that this represents hundreds of muscle contractions per day. This is indeed a significant workout.
The Vienna protocol, which has demonstrated success in clinical studies, exemplifies this approach by using sufficient amplitude to achieve tetanic contractions while maintaining patient tolerance. Studies using this protocol have shown meaningful increases in muscle mass and force production in chronically denervated muscles.
Clinical Application Guidelines
When working with denervated muscles using the RISE stimulator, follow these evidence-based guidelines:
We will be using wet sponge and rubber electrodes that are sized and positioned to cover as much of the affected muscle as possible. It's best not to obsess about a specific current value because it can change a little from session to session, depending on several things, such as:
How wet the electrodes are
How tightly they are secured to the skin
Start Low: Begin with the minimum current intensity that produces a visible, functional contraction. This is your therapeutic threshold. We will have guided you to find the optimal pulse width and other parameters.
Progress Gradually: Increase current only when necessary to maintain effective contractions as muscle condition improves—not simply to maximise intensity.
Monitor Continuously: Watch for signs of skin irritation, burns, or excessive discomfort. If these occur, reduce intensity immediately.
Prioritise Consistency: Focus on regular, sustained treatment rather than sporadic high-intensity sessions. Long-term compliance matters more than short-term maximum activation.
Optimise Electrode Placement: Use appropriately sized electrodes positioned to distribute current effectively, minimising current density at any single point.
The Path to Successful Outcomes
Successful denervated muscle rehabilitation requires patience and precision. The goal is sustainable, long-term treatment that preserves muscle tissue and supports functional recovery—not maximum short-term muscle activation that may cause harm or reduce patient adherence.
By understanding that more current is not necessarily better, clinicians can optimize their use of electrical stimulation to achieve the best possible outcomes for patients with denervated muscles. The RISE stimulator's ability to deliver appropriate current intensities with precise control makes it well-suited for this therapeutic approach.
The evidence is clear: finding and maintaining the minimum effective intensity, rather than pushing toward maximum tolerable levels, maximizes the potential for muscle preservation and functional improvement while minimizing risks and supporting long-term treatment compliance.