Recovering from surgery is not only about allowing the body to heal. It is also about gradually restoring strength, movement, coordination, and confidence.
One of the challenges patients can experience after orthopedic surgery is difficulty activating a muscle normally. This is especially common after procedures involving the knee. Pain, swelling, changes in movement, and the body's protective response after surgery can all contribute to muscle weakness.
Neuromuscular electrical stimulation, commonly called NMES, is one physical therapy modality that may help address this problem.
NMES uses electrical impulses to stimulate a motor nerve and create a muscle contraction. When appropriately applied, it can be used alongside therapeutic exercise to help patients activate and strengthen muscles during rehabilitation.
Research has shown potential benefits of NMES following procedures such as ACL reconstruction and total knee replacement, although results can vary depending on the surgery, timing, treatment parameters, and rehabilitation program.
What Is NMES?
Neuromuscular electrical stimulation is a form of electrical stimulation designed to activate motor nerves and produce a muscle contraction.
During treatment, a physical therapist places electrodes over or near the targeted muscle. The stimulation sends electrical impulses through the electrodes, causing the muscle to contract.
The goal is not simply to create a contraction. NMES can be incorporated into rehabilitation to help a patient practice activating a muscle that may be difficult to recruit voluntarily after surgery.
For example, someone recovering from knee surgery may have difficulty fully contracting their quadriceps. NMES can provide an additional stimulus to the muscle while the patient works on exercises such as quadriceps sets, straight-leg raises, or other strengthening activities.
Why Can Muscles Become Weak After Surgery?
Muscle weakness after surgery can happen for several reasons.
Pain and swelling can make it difficult to produce a normal muscle contraction. The nervous system can also temporarily reduce how effectively a muscle is activated.
This can be particularly noticeable in the quadriceps following knee surgery.
For patients recovering from ACL reconstruction, quadriceps weakness is a common rehabilitation challenge. A 2025 systematic review and meta-analysis of 11 studies involving 202 patients found that adding NMES to postoperative rehabilitation resulted in greater quadriceps strength improvements than standard physical therapy alone at both short- and longer-term follow-ups.
How Does NMES Work After Surgery?
NMES can support rehabilitation in several ways.
1. It can help produce a muscle contraction
Electrical stimulation activates motor nerves, which can create a visible and measurable muscle contraction.
This may be useful when a patient is having difficulty generating a strong voluntary contraction on their own.
2. It can help target muscle weakness
After surgery, certain muscles may become significantly weaker than they were before the procedure.
NMES can be used as an additional tool to target the affected muscle while the patient progresses through a strengthening program.
3. It can complement therapeutic exercise
One of the most important things to understand about NMES is that it is generally used as an adjunct to rehabilitation, rather than a replacement for exercise.
A physical therapist may pair NMES with active movement or strengthening exercises to combine electrical muscle activation with voluntary muscle control.
Research following ACL surgery supports this approach. Earlier systematic review evidence found that NMES combined with exercise may be more effective for improving quadriceps strength than exercise alone, although evidence for broader functional outcomes was less conclusive.
4. It may help address early postoperative weakness
The timing of NMES may be important.
A systematic review examining NMES after knee surgery found evidence supporting its use to assist quadriceps strength recovery, with some of the most favorable results occurring when NMES was introduced early after surgery and delivered at an adequate intensity.
However, the appropriate timing depends on the procedure, tissue healing, surgeon restrictions, and the individual patient's rehabilitation plan.
NMES After ACL Surgery
ACL reconstruction is one of the areas where NMES has been studied most extensively.
After ACL surgery, quadriceps weakness can make it difficult to perform basic movements and progress through rehabilitation.
A 2025 systematic review and meta-analysis found that patients receiving NMES in addition to standard rehabilitation had significantly greater improvements in quadriceps strength than patients receiving standard rehabilitation alone. The researchers also found that earlier use of NMES was associated with greater strength improvements.
This does not mean that NMES alone restores an athlete's strength or prepares them to return to sport.
Instead, NMES can be one piece of a progressive rehabilitation program that eventually includes strengthening, balance training, movement retraining, plyometrics, running, sport-specific training, and return-to-sport testing when appropriate.
NMES After Total Knee Replacement
NMES has also been studied following total knee arthroplasty, commonly called total knee replacement.
A systematic review and meta-analysis of nine randomized controlled trials involving 691 patients found that NMES improved quadriceps strength at multiple postoperative time points. The study also reported improvements in some measures of pain and physical function. However, the authors noted that several outcomes did not reach established thresholds for meaningful clinical improvement, so the size of the benefit should be interpreted carefully.
Another systematic review found that NMES may be particularly useful during the early postoperative period when quadriceps activation is difficult.
This is an important distinction.
NMES may help improve muscle activation and strength, but it should be viewed as one part of a larger recovery plan.
Can NMES Replace Strength Training?
No.
NMES is not intended to replace progressive strengthening.
As recovery progresses, patients typically need to regain the ability to voluntarily control and load their muscles through functional movements and progressively challenging exercises.
NMES can provide an additional stimulus when muscle activation is difficult, particularly during earlier stages of rehabilitation.
The long-term goal is to help the patient transition toward independent muscle activation, progressive resistance training, and functional movement.
What Does an NMES Session Feel Like?
Patients often describe NMES as a tingling or pulsing sensation followed by a muscle contraction.
The intensity can be gradually increased based on the patient's tolerance and the goals of treatment.
A physical therapist controls the stimulation parameters and electrode placement based on the muscle being targeted, the patient's condition, and the stage of rehabilitation.
NMES should feel like a strong muscle contraction rather than sharp or painful stimulation. Communication between the patient and therapist is important throughout treatment.
Is NMES Safe After Surgery?
NMES can be an appropriate rehabilitation tool for many postoperative patients, but it is not appropriate for everyone.
The timing and application of electrical stimulation should be determined by the patient's physical therapist and medical team.
Factors that may affect whether NMES is appropriate include:
- The type of surgery
- The stage of tissue healing
- Surgical restrictions
- Skin condition
- Sensation
- Medical history
- Presence of implanted electronic devices
- The location of the surgical site
- The patient's ability to tolerate stimulation
Patients should always tell their physical therapist about their medical history, medications, implants, and any concerns before beginning electrical stimulation.
Does More Electrical Stimulation Mean Better Results?
Not necessarily.
The effectiveness of NMES depends on more than simply turning up the intensity.
Research has found substantial variation in stimulation frequency, intensity, duration, electrode placement, timing, and treatment schedules across studies. These differences make it difficult to identify one universal NMES protocol for every postoperative patient.
A physical therapist can adjust these variables based on the patient's goals and response to treatment.
How NMES Fits Into Physical Therapy
At Core Performance Physical Therapy, modalities are used as part of a larger rehabilitation strategy.
For a postoperative patient, a physical therapy program may include:
- NMES
- Therapeutic exercise
- Progressive strengthening
- Mobility exercises
- Balance and stability training
- Manual therapy when appropriate
- Movement retraining
- Neuromuscular re-education
- Functional training
- Return-to-activity progression
The specific combination depends on the patient's surgery, goals, current abilities, and medical restrictions.
The purpose of using a modality is not simply to provide passive treatment. The larger goal is to help the patient progress toward stronger, more controlled, and more confident movement.
NMES vs. TENS: What Is the Difference?
NMES and TENS both use electrical stimulation, but they are generally used for different purposes.
NMES is designed to stimulate motor nerves and produce muscle contractions. It is commonly used when the goal is muscle activation, strengthening, or neuromuscular re-education.
TENS, or transcutaneous electrical nerve stimulation, is generally used for sensory stimulation and pain management.
They are not interchangeable.
This distinction is important because electrical stimulation is not one single treatment. Different types of electrical stimulation have different purposes, settings, and clinical applications.
What Does the Research Say?
Overall, research supports NMES as a potentially useful adjunct during postoperative rehabilitation, particularly for addressing muscle weakness.
Evidence is especially supportive following ACL reconstruction and total knee replacement.
A 2025 meta-analysis found significant improvements in quadriceps strength when NMES was added to rehabilitation following ACL surgery.
Research following total knee replacement has also found improvements in quadriceps strength and some measures of physical function when NMES is incorporated into rehabilitation.
At the same time, the evidence is not uniform. Studies use different stimulation parameters and rehabilitation protocols, and not every measured outcome shows a clinically meaningful improvement.
This is why NMES should not be promoted as a universal solution for postoperative recovery.
Instead, it is best viewed as one evidence-supported tool that may be useful for appropriately selected patients.
The Bottom Line
NMES may be a valuable tool for patients who experience muscle weakness or difficulty activating a muscle after surgery.
Research has shown particularly promising results for improving quadriceps strength following ACL reconstruction and total knee replacement.
However, NMES works best as part of a comprehensive physical therapy program. It does not replace progressive strengthening, movement training, or functional rehabilitation.
The goal of postoperative physical therapy is not simply to make a muscle contract. It is to help patients progressively regain strength, control, mobility, and confidence so they can return to the activities that matter to them.
Frequently Asked Questions
How soon can NMES be used after surgery?
The answer depends on the type of surgery, tissue healing, surgeon restrictions, and the patient's condition. Some research supports early NMES following certain knee surgeries, but the appropriate timing should be determined by the patient's rehabilitation team.
Does NMES hurt?
NMES typically produces a tingling sensation followed by a muscle contraction. The stimulation can be adjusted based on patient tolerance and treatment goals.
Can NMES build muscle?
NMES can contribute to muscle strengthening when it produces appropriate contractions, particularly when combined with active exercise. It should not be considered a replacement for progressive resistance training.
Is NMES only used after knee surgery?
No. NMES can be used in various rehabilitation settings where muscle activation or strengthening is a treatment goal. However, some of the strongest postoperative evidence is currently available for knee-related procedures.
How many NMES sessions will I need?
There is no universal number of sessions. Treatment frequency and duration depend on the patient's surgery, muscle weakness, rehabilitation stage, goals, and response to treatment.
Can I use NMES at home?
Some patients may be appropriate candidates for home electrical stimulation devices. However, proper electrode placement, settings, safety considerations, and treatment goals should be established with a qualified healthcare professional.
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