Reducing Spasticity and the Relationship with NMES Frequency

Neuromuscular electrical stimulation (NMES) is a therapy that influences muscle condition. It stimulates motor nerve endings by delivering a series of mild electrical impulses through the skin to the muscle, resulting in muscle contractions. The method is frequently used in neurorehabilitation to reduce spasticity — increased muscle tone and reflexes that often follow stroke, spinal cord injury, or cerebral palsy. Attention! NMES is not the same as selective stimulation (denervated) treatment! One of the key parameters of NMES is the stimulation frequency, which affects the muscle response and spasticity. In this article I present clinically proven data showing how different frequency ranges influence spasticity.

Frequency ranges and spasticity reduction

NMES treatment frequencies generally range between 1–100 Hz and can be divided into three main groups:

Low frequencies (~1–10 Hz)

They trigger isolated contractions of individual muscle fibers, perceived as fine twitches. Pulses are infrequent, so muscle fibers can partially relax between contractions.

In healthy muscle this range effectively helps relieve muscle stiffness due to pain. It is also often used to stimulate very weakened or atrophied muscles. In patients with high muscle tone it is less effective for immediate reduction of spasticity.

Medium frequencies (~20–50 Hz)

In this range pulses follow each other rapidly enough that the muscle fiber cannot relax; contractions summate and produce a continuous, tetanic-type contraction.

This range balances activation of slow and fast muscle fibers, so it is often used in NMES therapy to reduce spasticity and improve muscle strength. Stimulation at 20–50 Hz effectively reduces muscle tone without causing excessive muscle fatigue.

High frequencies (>50–80+ Hz)

They produce powerful muscle contractions but cause rapid muscle fatigue.

Although some studies indicate that the 50–100 Hz range may produce short-term spasticity reduction, overly frequent and prolonged application can instead increase muscle tone due to rebound reflexes.

For this reason most therapeutic protocols aimed at reducing spasticity avoid this frequency range to prevent unwanted effects.

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Practical application for clinicians and rehabilitation professionals

The first task is to choose the appropriate frequency. Generally the 20–50 Hz range is the most effective for reducing spasticity.

Applying reciprocal inhibition — stimulating the antagonist of the tight muscle — can help relax the spastic muscle. In other words, not only the spastic muscle but also its antagonist should be treated!

Treatment time is typically 15–30 minutes per day (on the same muscle). Muscle condition does not or only minimally improves after a single session. Persistent, regular application is necessary. After 2–3 months you typically reach the level of improvement that is achievable with stimulation. After stopping muscle stimulation, the muscle condition quickly (within weeks) returns to baseline. Think about it: if an athlete stops training, their muscles change.

Combination with other therapies: The effectiveness of NMES can be enhanced when combined with active exercise and functional training, and complemented by stretching, relaxing movements, foam rolling, and massage.

Patient education and home use

A patient with muscle spasticity can safely and effectively use muscle stimulation at home.

However, determining the appropriate treatment program, frequency, and pulse duration is the responsibility of the physiotherapist supporting them. Cooperation between the patient and therapist, with follow-up visits every few weeks, increases the success of NMES.

NMES can be an effective tool for reducing spasticity when applied with the right frequency and protocol.