Muscle Stimulation (NMES / EMS) in Rehabilitation: How It Works and the Evidence

What is NMES / EMS?

Neuromuscular electrical stimulation (NMES), also called electrical muscle stimulation (EMS), delivers small electrical pulses through pads on the skin to make a muscle contract. It is used in rehabilitation to help strengthen or re-activate muscles that are weak, under-used, or hard to switch on after injury or surgery.

It is important to distinguish NMES from TENS. NMES targets the motor nerves to produce a visible muscle contraction (the muscle actually moves). TENS targets sensory nerves purely to reduce pain and does not make the muscle contract.

How it works

The device delivers short electrical impulses that mimic the natural signal the nervous system sends to a muscle. This causes the muscle fibres to contract much as they would during voluntary exercise. The benefit is that a weakened or "switched-off" muscle can be made to work even when the person cannot fully activate it themselves — useful early after surgery or in neurological conditions.

The physiotherapist sets the electrode placement, intensity, and timing so the contractions are effective but comfortable, and combines the stimulation with active exercise.

What it is used for

Common uses in physiotherapy include:

• Strengthening the quadriceps after knee surgery or ACL reconstruction
• Reducing muscle weakness and disuse atrophy during immobilisation or illness
• Supporting muscle re-activation and function after stroke
• General strengthening as an adjunct to an exercise programme

What the evidence says

The evidence is strongest for building muscle strength when NMES is added to exercise, rather than used alone.

A 2025 systematic review of trials after ACL knee surgery found NMES added to standard rehabilitation significantly improved quadriceps strength, with the largest benefit when started within about a week of surgery. In stroke rehabilitation, a 2021 review found NMES improved activities of daily living, especially for the upper limb in the subacute stage. Reviews also support NMES for helping prevent muscle weakness in immobilised or critically ill patients.

The honest caveat is that benefits are most consistent for muscle strength rather than overall function, and trials vary in quality and settings. NMES is an adjunct to active rehabilitation, not a substitute for exercise.

Using it at home

Compact, battery-powered NMES units let a physiotherapist-set programme continue between visits, which can help maintain progress. Because effective, safe use depends on correct electrode placement, intensity, and dosage, your therapist should set these up and confirm the programme before you use the device independently.

Safety and contraindications

NMES is widely used and generally safe, but some people should avoid it or check first.

• Avoid with a pacemaker or implanted defibrillator.
• Avoid over the pregnant abdomen or lower back.
• Avoid over the front of the neck, the eyes, or the mouth.
• Do not use over broken, infected, or numb skin.
• Avoid over known or suspected cancerous tissue, and clear use with a qualified clinician first.

Sources

• Li Z, et al. NMES on quadriceps strength and knee function after ACL surgery: review & meta-analysis, 2025
• NMES improves activities of daily living post-stroke: systematic review & meta-analysis, 2021
• Maffiuletti NA, et al. NMES for preventing muscle weakness and wasting in critically ill patients. BMC Medicine, 2013

Other modalities

• TENS (transcutaneous electrical nerve stimulation)
• Therapeutic ultrasound
• Interferential current therapy (IFC)
• Heat and cold therapy
• Low-level laser / red-light therapy (LLLT)
• Resistance bands
• Weights & resistance training
• Pneumatic resistance training
• Cable functional trainer
• Motorised cycling therapy
• Supported treadmill gait training