Electrical Stimulation: TENS, NMES, and Iontophoresis Concepts — Physical Therapy / Rehab Aide

Objective. Students will identify the components of a TENS and NMES unit, describe the physiological rationale for each clinical use, correctly place electrodes on a peer following a written protocol, and recognize adverse skin responses that require halting treatment.

What Is Electrical Stimulation?

Electrical stimulation (e-stim) uses a controlled low-level electrical current delivered through the skin to produce a therapeutic effect. As a PT aide, you will not select parameters or initiate treatment independently — that is the supervising physical therapist's responsibility. You will, however, prepare equipment, set up electrodes following a written protocol, monitor patients during treatment, inspect the skin before and after, and report any changes immediately. Understanding how each modality works makes you a safer and more effective team member.

TENS — Transcutaneous Electrical Nerve Stimulation

TENS stands for transcutaneous electrical nerve stimulation. "Transcutaneous" means through the skin. TENS delivers electrical pulses to peripheral sensory nerves with the primary goal of reducing pain. It does not cause visible muscle contraction at typical clinical settings.

Physiological rationale: The most widely accepted explanation is the gate control theory of pain. Large-diameter sensory nerve fibers (Aβ fibers), when stimulated by TENS, can inhibit pain signals carried by smaller fibers (Aδ and C fibers) at the level of the spinal cord — essentially "closing a gate" to pain transmission. Certain TENS settings may also promote release of endorphins, the body's natural pain-relieving chemicals.

Common parameters (set by the PT; you confirm you are starting at zero):

Pulse rate (frequency): measured in pulses per second (Hz)
Pulse width (duration): measured in microseconds (µs)
Amplitude (intensity): increased gradually until the patient reports a comfortable tingling; never increased to the point of pain or strong muscle contraction during conventional TENS

TENS unit components you must recognize:

Main unit (battery-powered or plug-in)
Lead wires (connect unit to electrodes; inspect for fraying)
Self-adhesive electrodes (inspect for dry or cracked gel, damaged backing)
Parameter dials or digital controls (pulse rate, pulse width, amplitude)

NMES — Neuromuscular Electrical Stimulation

NMES uses electrical current to cause visible muscle contractions by stimulating motor nerves. Common clinical uses include strengthening weakened muscles, re-educating movement patterns after injury or surgery, and reducing muscle atrophy during recovery. Because NMES produces muscle contraction, the sensation is stronger than TENS and setup must be precise to target the correct muscle group.

Physiological rationale: The electrical pulse depolarizes motor nerve fibers, causing the muscle to contract just as a voluntary contraction would, recruiting motor units in a reproducible way. Over time, repeated contractions can improve strength and neuromuscular control.

Key difference from TENS: TENS targets sensory nerves for pain relief; NMES targets motor nerves to produce contraction. The two modalities can sometimes look similar as equipment but are used for different purposes.

Iontophoresis — Concept Overview

Iontophoresis uses a very low-level direct current to drive charged medication molecules through the skin. A medicated electrode (charged to match the medication's charge) repels the drug into tissue, reducing inflammation or decreasing pain at a specific site without a needle injection.

Aide scope of practice — critical point: Loading the medicated electrode, selecting the medication, and setting dosage parameters are outside the PT aide's scope of practice. The PT or licensed clinician handles those steps under a physician order. As an aide, your permitted tasks include:

Positioning the patient comfortably
Inspecting the skin before treatment (report redness, open areas, or rash to the PT)
Inspecting the skin after treatment (report any new reactions immediately)
Documenting observations and reporting to the supervising PT
Assisting with patient comfort during treatment

You must never apply or remove the medicated electrode, adjust current, or interact with medication components.

Electrode Placement Essentials

Proper electrode placement is one of the most important tasks an aide performs with e-stim. Always follow the written protocol card provided by the supervising PT. General principles:

1. Skin preparation: Clean the skin with an alcohol wipe and allow it to dry fully. Remove oils and debris so the electrode adheres evenly.

2. Electrode inspection: Check each electrode for dried or cracked gel, tears, or missing sections. A damaged electrode can concentrate current and cause a burn — discard and replace it.

3. Placement: Position electrodes firmly and smoothly; no air pockets under the edges.

4. Lead wire connection: Connect lead wires to electrodes before connecting to the unit, or verify amplitude is at zero before connecting to an already-powered unit.

5. Starting amplitude: Always confirm the amplitude dial or setting reads zero before turning on the unit and before connecting to the patient. This is a non-negotiable safety step.

6. Patient instruction: Tell the patient what sensation to expect (tingling for TENS, thumping or pulling for NMES), instruct them to report discomfort, burning, or unusual pain immediately, and show them how to call for help.

7. Gradual increase: Increase amplitude slowly, pausing to check in with the patient at each step.

8. Removal: Turn amplitude to zero, disconnect unit, remove electrodes gently, inspect skin for redness or irritation.

Adverse Skin Responses — Stop Treatment Immediately

You must halt treatment and notify the supervising PT if you observe or the patient reports:

Skin redness that does not fade within a few minutes after electrode removal
Blistering, burns, or open areas
Unusual or increasing pain under an electrode
Skin rash or allergic reaction
The patient reports a metallic taste (possible sign of current spread near the face — relevant to know for other body regions)
The patient becomes distressed, reports dizziness, or shows any sign of adverse reaction

Document your observations and report promptly. Never attempt to treat a skin reaction yourself.

Contraindications to Know

The PT screens patients for contraindications. As an aide, be aware of absolute contraindications so you can flag concerns before setup: electronic implants (such as pacemakers), placement over the carotid sinus (neck), placement over a gravid (pregnant) uterus, placement over an area of impaired sensation where the patient cannot report discomfort, and open wounds unless specifically ordered. If you observe anything that concerns you, stop and ask the PT before proceeding.

Key terms8

Transcutaneous electrical nerve stimulation (TENS)A modality that delivers low-level electrical pulses through the skin to stimulate sensory nerves for the primary purpose of pain relief, without causing muscle contraction at typical settings.

Neuromuscular electrical stimulation (NMES)A modality that uses electrical current to stimulate motor nerves, producing visible muscle contractions to improve strength, re-educate movement, or reduce atrophy.

Gate control theoryA widely used explanation for TENS pain relief: stimulation of large-diameter sensory fibers inhibits pain signals from smaller pain-carrying fibers at the spinal cord level, reducing perceived pain.

IontophoresisA modality that uses low-level direct current to drive charged medication molecules through the skin to a target tissue; medication loading and parameter setting are outside PT aide scope.

Amplitude (intensity)The strength of the electrical current delivered to the patient, measured in milliamps (mA); always started at zero and increased gradually based on patient feedback.

Pulse rate (frequency)The number of electrical pulses delivered per second during e-stim treatment, measured in hertz (Hz); selected by the PT based on treatment goal.

Pulse width (duration)The length of each individual electrical pulse, measured in microseconds (µs); influences which nerve fibers are recruited.

Electrode inspectionA required safety check before every treatment to confirm electrodes have intact gel, no cracks or tears, and proper adhesion; damaged electrodes must be discarded to prevent skin burns.

In class: Instructor demonstration using a clinical TENS unit: instructor narrates aloud each step — equipment inspection, lead wire check, electrode inspection and placement for a generic lower-back protocol, parameter dial setting (pulse rate, pulse width, amplitude starting at zero), patient instruction script, gradual amplitude increase, and removal procedure; students follow along on a printed setup checklist. · Guided practice: in supervised pairs, students place TENS electrodes on the forearm (a low-risk region used for training) per a written protocol card, increase amplitude until the peer reports a comfortable tingling sensation, maintain for a brief supervised period, then remove electrodes and inspect skin; instructor circulates and coaches each pair before signing off on the checklist. · Iontophoresis concept station: because iontophoresis medication loading is outside aide scope, students complete this as an analysis activity — they read an equipment manufacturer patient-education sheet, identify the parts of the electrode delivery system, list aide tasks that are permitted (patient positioning, skin inspection before and after, reporting), and record what must be done only by the PT or under direct PT order; results discussed as a group.
Materials: Clinical TENS units (multiple), NMES unit (for demonstration), lead wires, self-adhesive electrodes (assorted sizes), alcohol wipes, electrode inspection checklist, written protocol cards, iontophoresis equipment manufacturer patient-education sheet, setup checklist forms, treatment tables
Check: Instructor-signed setup checklist: student must complete all safety steps (zero amplitude before connection, electrode inspection, patient instruction given) with zero critical errors; overall checklist score of at least 80% required to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.