User Guide to Neuromuscular Electrical Stimulation (NMES)
The NMES Parameters Guide
The goal of NMES is to contract as many muscles fibers to generate as much force as possible. Parameters are how we ensure we achieve this for each patient at each session. What you need to know:
Pulse Duration. Pulse durations between 400 and 600 μs target motor neurons and are most effective in torque production while also minimizing fatigue and metabolic demands. They also produce greater quadriceps cross-sectional activation compared to shorter pulse durations. Widen your pulse duration whenever possible.
Pulse Frequency. Higher pulse frequency correlates with higher force production, but also to pain and fatigue. Too low, no muscle contraction. Too high, pain. Keep pulse frequency between 30-50 Hz.
Duty Cycle. Weak and inhibited muscles will need a lot of rest during training. Pair that with NMES targeting primarily fast fatigable muscle fibers. To reduce the impact of fatigue, the duty cycle (or "on / off" time) of 1:5 is recommended. Keep in mind: Not all stimulators are capable of programming this, so it may be necessary to do it manually.
Amplitude / Intensity. Higher intensity means increased motor unit activation, force generation, and cross-sectional area of the quadriceps activation. NMES force production should be greater than 50% of the maximal voluntary contraction. The challenge with delivering maximum intensity is pain and fatigue increase. Communicate the importance of strong stimulation to your patient and always deliver the Maximum Tolerable Intensity (MTI).
Electrode Placement, Size, and Number. Increasing the number of stimulating electrodes and placements over motor points minimize fatigue and patient discomfort while improving torque production. Larger pads can help too. New, moist pads with excellent skin contact are best for reducing internal resistance and improving likelihood of constant current. Shaving the hair is an annoying, but simple step to improving results.
These tips are based on an excellent review by Neil Glaviano and Susan Saliba. It was published in Sports Health in 2016.
You can also download the University of Delaware’s guide based on their recently publication in JOSPT (2024) by clicking here and view the video they released with this publication at the bottom of this page.
Why should you care about parameters?
Electrical circuits are complex. Turning your patient into an electrical circuit is even more complex! We have a full post on how NMES works and how to tune parameters to each patient.
In brief, our nerves are selectively sensitive to electrical stimulation based on two main parameters: (1) Stimulus Intensity and (2) Pule Duration. Not every patient has the same sensitivity, nor do they have the same internal resistance from day to day. Parameters are how we modify the treatment to ensure optimal effects.
Stimulator specifications. Most stimulators offer a range of pulse width, but encourage iteratively tuning intensity during set-up. The plot below indicates the maximum intensity and pulse duration assuming a 1000 ohm internal resistance.
Notice how most products hug the left axis, aiming for lower pulse duration and tuning to higher intensities. Handheld stimulators tend to cluster at maximums of 100-120 mA and < 400 micro-second pulse durations. Newer products, like the KneeHAB and QB1 leverage wider pulse durations and require lower intensity output - a feature that is likely more comfortable for patients and achieves better constant current.
Consistent current depends on capacity. When linking weak batteries together, there is a trade-off between voltage and current. Most handheld stimulators (i.e., Continuum, TENS7000, EMPI 300pv) are powered by 2xAA (1.5 V) or single 9 V batteries. This means that in order to generate constant current of 100mA and maintain a steady contraction, the batteries need to be near-new. Dead batteries, or worn-out rechargeable batteries, common to most clinics I've worked in just won't cut it.
This is the clear advantage of clinical stimulators. Clinical stimulators are plugged into 120V outlets and don't fall prey to waning capacity.
Don’t have a clinical stimulator? That is fine. Handheld units are better than nothing, but take steps to minimize internal resistance and ensure consistent current! I am happy to share strategies for achieving this. Reach out to me (dave@live4pt.com) or join our member area.
The University of Delaware’s NMES User Guide Video featured in the supplemental material of their 2024 paper in JOSPT (Arhos et al., 2024)
