Neuromuscular Electrical Stimulation (NMES)

Overview

Is a machine that sends a message to a muscle to have it repeatedly fire to increase strength and/or endurance
Involves putting electrodes on skin
- Aim to put one electrode at one end of the muscle and one electrode at the other end of the muscle
Works by the electrodes activating the motor nerve that is in the muscle through action potentials being generated by the current from the machine
Can be used to help patients do a specific muscle action or do a functional activity
Can be used when a patient has muscle atrophy, muscle weakness, or to work on neuromuscular retraining

YouTube. How to set up for NMES for Wrist Extension? thumbnail image. YouTube video ID sRdi3pM5sf0.

Machine Settings

Intensity: Subjective sensation a patient experiences regarding how strong the muscle contraction is

Gradually increase the intensity on the machine until a good, strong contraction is formed

Duty Cycle: Ratio of how much time the muscle is firing versus how much time the muscle is relaxing

General rule is weaker muscles require more rest between contractions, while stronger muscles don't require as much rest
A common time frame set for a muscle to contract is for 10 seconds at a time
General rule is weak muscles that are experiencing significant atrophy should have a duty cycle of 1:9 (10 seconds on, 90 seconds off)
General rule is strong muscles for patients who are at the end of rehab should have a duty cycle of 1:1 (10 seconds on, 10 seconds off)

RAMP: Setting which adjusts the build up at the start and decline at the end of a muscle contraction

Can be adjusted for patient comfort and to mimic a natural muscle contraction
General rule is for the build up to be longer than the decline
A typically used setting for RAMP during a 10 second firing period is for a 2 second build up and 1 second decline

Pulse Frequency: How often the NMES machine sends out small micro pulses per second (measured in Hertz, Hz)

1 Hz = 1 pulse per second
General rule is to use between 10 and 50 Hz, which is a good balance between muscle contraction being strong but not causing too much fatigue
How it works: Constant pulses need to be sent out in order for action potentials to occur in the motor nerve for the muscle contraction to occur

Pulse Duration: The amount of time each individual micro pulse from the frequency setting lasts

The unit this is measured in is microseconds (1 millionth of a second!)
General rule is 350-450 microseconds for the most optimal, strong muscle contraction to occur
How it works: Longer pulse durations result in stronger contractions, as the muscle receives a more sustained stimulus

Common Electrode Placement

While the general rule is to place an electrode at each end of the muscle being targeted (origin and insertion), you may need to play around with electrode placement to get the targeted muscle to fire most optimally by moving it slightly from where you first placed it

Indications

Muscle atrophy or weakness
Peripheral neuropathy
Neuromuscular retraining (such as after a stroke or nerve injury)
Edema/swelling
Spasticity (fatigues the spastic muscle(s) or stimulates the antagnoist muscle(s)

Contraindications:

Arterial artery disease
Active infection
Deep vein thrombosis
Epilepsy
Hemorrhagic conditions or recent bleeding
Impaired sensation
Irritated skin
Pacemaker
Pregnancy
Tumor present in treatment area
- However, generally IFC can still be used if these contraindications are not present in the upper extremity

Quiz Questions

What type of nerve does NMES primarily stimulate to cause a muscle contraction?

A. Sensory afferent nerve

B. Motor nerve

C. Autonomic nerve

D. Interneuron

What is the primary goal of NMES therapy?

A. Stimulate sensory nerves for pain relief

B. Cause repeated muscle contractions to increase strength or endurance

C. Relax the muscle with constant vibration

D. Deliver medication through the skin

What is the recommended duty cycle for a significantly weak or atrophied muscle?

A. 1:1 (10 sec on, 10 sec off)

B. 1:4 (10 sec on, 40 sec off)

C. 2:5 (10 sec on, 25 sec off)

D. 1:9 (10 sec on, 90 sec off)

Why is the ramp setting used during NMES treatment?

A. To deliver slight heat during contraction

B. To maximize electrical penetration to the targeted muscles

C. To gradually build and reduce contraction for comfort and natural movement

D. To improve skin conductivity for comfort

What is the typical pulse frequency range for NMES to balance contraction strength and fatigue?

A. 1–5 Hz

B. 60–100 Hz

C. 10–50 Hz

D. 200–300 Hz

Which of the following is an appropriate indication for NMES use?

A. Joint stiffness due to a bony block

B. Presence of a trigger point in a muscle

C. Muscle weakness after stroke

D. Malignancy in the treatment area

Which of the following patients would most likely benefit from a 1:1 duty cycle during NMES?

A. A patient near the end of rehab with good strength

B. A patient with peripheral neuropathy

C. A patient in early rehab with severe weakness

D. A patient who had a stroke less than 24 hours ago

What role does NMES play in managing spasticity?

A. It relaxes the affected muscle by stimulating the surrounding connective tissue

B. It fatigues the spastic muscle or stimulates its antagonist

C. It activates sensory nerves to dull the spasm

D. It blocks neural input from the spinal cord to the spastic muscle

Quiz Answers

References

Byars, G., Glines, R., Stephenson, S., & Thompson, M. (2023). Electrical Physical Agent Modalities. https://slcc.pressbooks.pub/otaphysicaldysfunction/chapter/electrical-physical-agent-modalities/

Doherty, C. (2022). Neuromuscular Electrical Stimulation (NMES): What it is, how it is applied and a summary of evidence. YouTube. https://www.youtube.com/watch?v=ixad3cXnkCA

Neuromuscular Electrical Stimulation (NMES). (n.d.). Electrotherapy On The Web. https://www.electrotherapy.org/muscle-stimulation-nmes

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