NMES after knee replacement may help when your quadriceps remain difficult to activate despite exercise and consistent participation in physical therapy. Neuromuscular electrical stimulation uses electrical current to produce a purposeful muscle contraction.
NMES is not a replacement for exercise. It may help recruit the quadriceps so that active exercise becomes more effective when swelling, pain, and nervous system inhibition are limiting voluntary contraction.
In Episode 40 of the Total Knee Success Podcast, Michelle Losurdo, PT, DPT, OCS, explains how NMES differs from other electrical stimulation, what influences its effectiveness, and why individualized instruction is essential.
How NMES after knee replacement works
After knee replacement, swelling, pain, surgical trauma, and altered information coming from your joint can interfere with communication between your nervous system and quadriceps. This is called arthrogenic muscle inhibition.
The muscle may be physically present and capable of producing force, but your nervous system may not recruit enough muscle fibers to create a strong contraction. This can affect walking, stair use, balance, and standing from a chair.
NMES delivers electrical stimulation through electrodes placed on the skin over the muscle. The stimulation activates motor nerves and creates a visible quadriceps contraction. When appropriate, a person may also contract the muscle voluntarily during the stimulation cycle under professional guidance.
NMES does not replace strengthening. It can help your quadriceps participate more effectively in the strengthening process.
That distinction is important. Electrical stimulation is an adjunct to rehabilitation, not a stand-alone solution for weakness, walking difficulty, or instability.
NMES and TENS are not interchangeable
TENS stands for transcutaneous electrical nerve stimulation. It is generally used for symptom relief and targets sensory nerves. It commonly produces tingling or buzzing without a strong muscle contraction.
NMES is intended to activate motor nerves and produce a muscle contraction. It typically uses different pulse durations, timing, and intensity than TENS. Simply increasing the intensity of a TENS unit does not reliably convert it into an NMES device.
Interferential current is another form of electrical stimulation commonly used for symptom management in rehabilitation settings. It is not the same as quadriceps NMES.
Some NMES may be delivered using Russian stimulation, a medium-frequency current delivered in bursts. Russian stimulation is frequently available in clinical equipment, where a therapist can adjust its parameters and intensity.
Visible contraction is central to NMES
When NMES is being used for muscle activation, a mild tingling sensation without visible quadriceps contraction is unlikely to provide the intended strengthening stimulus. Research protocols generally use stimulation strong enough to produce a substantial contraction.
However, stronger stimulation must still remain tolerable and safe. The correct intensity cannot be selected from a general article because sensation, skin condition, muscle activation, medical history, and device capabilities differ.
A physical therapist can demonstrate the intended contraction, electrode placement, device settings, and how NMES fits with active exercise. Professional instruction is particularly important before attempting home use.
If you have not read the previous article, Episode 39 explains why quadriceps weakness after knee replacement can change walking, stair use, and confidence.
NMES devices for home use
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If your physical therapist has recommended home NMES and has taught you how to use it, this NMES unit for quadriceps muscle contraction is one device you can review with your therapist. A second electrical stimulation unit provides another option to compare.
These links are not a recommendation to begin NMES independently. Before purchasing, confirm that the device provides true NMES, allows the required settings, and is appropriate for the treatment plan your clinician has selected. Product descriptions that use the words “TENS” and “muscle stimulation” together require careful review because the available modes may differ.
Electrode size and placement affect the experience
Larger electrodes are generally used over the quadriceps because they distribute current across a broader area. Very small electrodes can concentrate the current and feel uncomfortable before producing a useful contraction.
Electrodes must remain on intact muscle tissue and away from the surgical incision. Exact placement depends on anatomy, device configuration, muscle response, and the goal of treatment. Incorrect placement can produce an uncomfortable sensation without recruiting the intended portion of the quadriceps.
Skin should be clean and intact. Lotion, oil, dense hair, damaged electrodes, and poor contact can interfere with adhesion and current delivery. Skin should be checked before and after each session.
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NMES requires important safety screening
NMES should not be applied over broken or irritated skin, an open wound, active infection, or a surgical incision. Electrodes should not be placed across the chest or over the front of the neck.
People with implanted electrical devices, including pacemakers or defibrillators, need explicit medical clearance. Sensory loss, circulation problems, seizure history, and other medical conditions may also require additional precautions or make NMES inappropriate.
Stop using the device and seek professional guidance if stimulation causes sharp pain, unusual symptoms, persistent skin irritation, or another concerning response. Manufacturer instructions do not replace individualized screening.
Timing and consistency influence results
Research has found that NMES added to standard rehabilitation can improve early quadriceps strength and functional performance after knee replacement. Studies showing benefit have often begun NMES early and used it consistently at sufficient intensity.
That does not establish one universal schedule. Frequency, intensity, contraction time, rest time, electrode placement, and the accompanying exercise must be selected for the individual. Applying electrical stimulation occasionally at a low sensory level is different from a structured NMES program designed to recruit the quadriceps.
NMES is one possible tool within a broader plan that may include swelling management, active quadriceps work, progressive strengthening, walking practice, balance activities, and functional training.
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References
- Stevens-Lapsley JE, Balter JE, Wolfe P, Eckhoff DG, Kohrt WM. Early neuromuscular electrical stimulation to improve quadriceps muscle strength after total knee arthroplasty: a randomized controlled trial. Phys Ther. 2012;92(2):210-226. doi:10.2522/ptj.20110124
- Churchill L, Bade MJ, Koonce RC, Stevens-Lapsley JE, Bandholm T. The past and future of peri-operative interventions to reduce arthrogenic quadriceps muscle inhibition after total knee arthroplasty: a narrative review. Osteoarthritis Cartilage Open. 2024;6(1):100429. doi:10.1016/j.ocarto.2023.100429
- Arhos EK, Stevens-Lapsley JE, Schmitt LC. Who’s afraid of electrical stimulation? Let’s revisit the application of NMES at the knee. J Orthop Sports Phys Ther. 2024;54(2):72-83. doi:10.2519/jospt.2023.12028
- Li Z, Wang Q, Chen G, et al. Effects of neuromuscular electrical stimulation on quadriceps muscle strength and physical function in patients after total knee arthroplasty: a systematic review and meta-analysis. Front Med. 2025;11:1493912.
- Jette DU, Hunter SJ, Burkett L, et al. Physical therapist management of total knee arthroplasty. Phys Ther. 2020;100(9):1603-1631. doi:10.1093/ptj/pzaa099
Educational disclaimer: This article provides general educational information and does not constitute medical advice, diagnosis, or treatment. NMES requires individualized screening, device selection, electrode placement, dosing, and instruction from a qualified healthcare professional. Do not begin electrical stimulation based solely on this article.