ETS – biofeedback-controlled stimulation

What is ETS, and why is it called a breakthrough in modern rehabilitation?

ETS is a modern and effective electrotherapy treatment method—primarily used to regain lost functions. Its two main areas are motor recovery after stroke (relearning movement) and the treatment of urinary/fecal incontinence.

What distinguishes it from conventional muscle stimulation: EMS stimulation is passive—you place the electrodes and the device's pulses work the muscles without you doing anything. ETS, however, only stimulates when you actively participate, for example when you voluntarily try to perform a movement. The ETS device detects attempts at muscle activation—even when they produce little or no visible motion. When that attempt reaches a preset threshold, the device "boosts" the contraction with stimulation and triggers a full muscle contraction. This is the key to active, volitional rehabilitation—the motor of the brain’s neural "rewiring."

What does ETS mean — breaking down the acronym

ETS is the abbreviation of the English term "EMG-Triggered Stimulation". In Hungarian it could be translated as "EMG-triggered stimulation," but I prefer the phrasing "biofeedback-controlled stimulation" because it more accurately reflects how it works.

• EMG: short for Electromyogram — the recording of a muscle's electrical activity. It's like an EKG for the heart, except the signal is recorded from a skeletal muscle rather than the heart muscle.
• Triggered: means "initiated by some phenomenon." For example, if you nudge a glass, the water may spill. The "trigger" is the movement, and the spilling is the resulting consequence.
• Stimulation: in this context, it means contraction of muscles induced by electrical impulses. With an appropriate impulse even a paralyzed muscle can be caused to contract.

So ETS = the muscle's own electrical signal initiates the added stimulation. You want to move — the device assists.

How does ETS work in practice?

When using ETS, the device continuously monitors the electrical activity (EMG) of the target muscle. As more muscle fibers activate (the stronger you try to contract the muscle), the recorded electrical signal increases. The process occurs in steps:

1. Threshold setting: the device either automatically determines the threshold at the start of each session, or the therapist can set a value that defines how much EMG is required to trigger the assistive stimulation. In the early phase the threshold is low—very weak attempts will suffice.
2. Voluntary attempt: you try to move the muscle. There may be no visible motion or only a slight twitch—but the EMG detects the attempt.
3. Threshold reached: if the EMG signal reaches the preset level, the device immediately initiates stimulation.
4. Stimulation "assist": the stimulator delivers a full muscle contraction using the preprogrammed impulse parameters (frequency, pulse width, intensity, duration).
5. Feedback: the device displays or signals audibly that the attempt "succeeded"—this is motivating for the patient and supports persistence.
6. Gradual threshold increase: as the muscle strengthens, the threshold is raised so that progressively greater voluntary effort is required to trigger the stimulation. This is progressive training.

EMG is very sensitive—it registers even the faintest intention in a limb that appears totally "paralyzed." A weak attempt can be electrically detected even if no visible movement occurs. This has enormous psychological importance: the patient senses that the intention is "there," only the muscle is struggling to activate. A 2022 systematic review found that in 20 of 24 studies of sEMG-based interventions (including ETS) measurable improvements were seen in upper-limb outcomes after stroke.⁶

When do we use ETS? — Main applications

ETS has had its greatest successes in two areas: post-stroke motor rehabilitation and incontinence treatment. But it is useful in other situations as well:

What is brain plasticity, and why is it important for ETS?

Brain plasticity (neuroplasticity) is the brain's capacity for anatomical and functional change. Throughout life the brain continuously modifies its physical structure and reshapes its "circuits." This ability is based on the formation of new synaptic connections and the reorganization of existing neural links—this is the physiological foundation of learning.

After brain injury (e.g., stroke) the brain can even grow new axons. If certain brain areas "fail," other areas can take over their tasks. Plasticity is therefore the brain's adaptability to changing environmental conditions.

A 2019 professional synthesis summarizes 15 evidence-based principles of motor learning that determine stroke rehabilitation effectiveness: intensive and frequent repetition, task specificity, multisensory feedback, motor imagery, action observation, combined KP/KR (knowledge of performance / results) feedback.⁸ ETS fits precisely with these principles: active attempts + real-time feedback + repetition.

See it in action — DuoBravo ETS demonstration

The video below demonstrates practical use of the DuoBravo N device. You can see the essence of the German clinical protocol, the settings, and some typical applications:

What does the research say about ETS?