Foundations of Electrical Stimulation
PTA 101 Intro to Clinical Practice 1

Instructional Use Statement

The following information is used for instructional purposes for students enrolled in the Physical Therapist Assistant Program at Lane Community College. It is not intended for commercial use or distribution for commercial purposes. It is not intended to serve as or take the place of medial advice or treatment.


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Electrical stimulation use dates back to ancient time when electric eels were used to treat painful spines and limbs. In this lesson, we will study characteristics of electricity, electricity effects in biological tissue, and its use in rehabilitation. By understanding how electrical stimulation effects muscle and nerve function, we can safely and effectively select the most appropriate "estim" to maximize patient progress toward goals in the plan of care.


Lesson Objectives

After completing this lesson, the successful student will be able to:

  1. Describe the key terms, principles, and theory of electrical stimulation.
  2. Describe the physiologic effects of electrical stimulation.
    1. Describe the three major forms of current used in electrical stimulation Describe common electrical stimulation devices and their clinical indications.
  3. Describe expected goals and outcomes for application of electrical stimulation.
  4. Recognize precautions and contraindications to electrical stimulation.
  5. Define electrical stimulation parameters (i.e., frequency, duty cycle, ramp time, waveform, pulse rate, pulse duration, and treatment duration).
  6. Describe the properties and configuration of electrodes used in electrical stimulation Identify the role of the PTA during application of electrical stimulation.




Overview of Electricity and Physiology


All use of electricity to produce a change in body tissue is directly related to the properties of the cell membrane. Electricity can stimulate ionic flow, and therefore action potentials, which result in activation of nerve pathways, muscle tissue, and chemical changes

Review the process of an action potential at the cell membrane.

(Approximately 7 minutes)

This will refresh your understanding of cellular physiology and help make connections between physiology and electrical stimulation as a rehabilitation modality


Key Terms and Law's of Electricity

Approximately 9 minutes

More about Ionic Flow

Approximately 3 minutes

This excerpt from the American Society of Neurological Monitoring has one of the best explanations I've seen to help understand ionic flow in biological tissue:

"How an Electrical Stimulator Works

In an electrical stimulator, the flow of anions (-) and cations (+) is controlled by the mechanics of the circuitry within the stimulator.  The stimulator is unique in that the cathode is the negative pole (-) because it discharges anions (-), and the anode is the positive pole (+) because it discharges cations (+). At the end of the day, that's the fundamental difference between a battery and a stimulator.

Depending on how we configure the polarity, the stimulator will discharge either cations or anions into the body part being stimulated.

In cathodal stimulation, anions (-) are discharged into the body as current flows from the cathode (-), through the tissue, and back to the anode (+).

In anodal stimulation, cations (+) are discharged into the body as current flows from the anode (+), through the tissue, and back to the cathode (-).

Now, let's imagine that we place an electrical stimulator on the surface of the skin with a nerve bundle running underneath (Figure 2). Within the nerve bundle is a single nerve fibre (axon) upon which we will focus.

At rest, the inside of a cell is more negative than the outside of a cell.

This occurs because there is a slightly greater number of negative charges than positive charges inside of the cell (intracellular space), and a slightly greater number of positive charges than negative charge outside of the cell (extracellular space). Because of the electrical difference, the cell is said to be polarized- just like a magnet, one side is more positive and the other side is more negative. If the electrical gradient were suddenly reversed, the cell would be depolarized, and we might see an action potential."

(Reference: Vogel, R. W. (2017, December). Understanding Anodal and Cathodal Stimulation [Blog post]. American Society of Neurophysiological Monitoring. Retrieved from


Below is a table view of the difference between a contraction elicited through normal central nervous system function as compared to that via electrical stimulation.

Motor Unit Recruitment - Central Nervous System

Motor Unit Recruitment and Contraction - Electrical Stimulation



Small type I motor units are recruited first then larger type II motor units for smooth and gradual tension

Large superficial fatigable type II motor units are recruited first, then smaller motor units

Asynchronous firing in off and on pattern - energy efficient and slower onset of fatigue

Synchronous firing - motor units stimulated continue to fire until stimulus removed, causing quick onset of fatigue

Action potential moved away from the nerve cell body

Action potential generated in two directions, away from the cell body and back toward the cell body



Three Major Types of Current Used in Electrical Stimulation (estim)

Approximately 6 minutes

There are three basic waveforms used in commercial therapeutic electrical stimulation units: direct current, alternating current, and pulsed current.

Direct Current (DC) - Galvanic

Alternating Current (AC) - Biphasic

Pulsed Current (pulsed - AC and DC)



Electrical Stimulation Names and Indications

Approximately 9 minutes

There are four common clinical names that describe electrical stimulation devices:


Electrical Stimulation Device

Type of Current

Summary of Action


AC - Burst modulation

uses current to depolarize muscle and stimulate a muscle contraction

High Volt Pulsed Current (HVPC)

monophasic, pulsed

uses high intensity, short duration, pulsed current to promote charge accumulation in the tissue

Interferential Current (IFC)

amplitude- modulated AC

asynchronous waves interfere and produce a pain modulating effect; uses four electrodes

Low intensity direct current (LIDC; Microcurrent)

DC or monophasic pulsed

uses unidirectional flow of current to accumulate a charge in tissue


In addition to the common practice of referring to electrical devices when talking about electrical stimulation (ES or "estim), there are three common acronyms that describe types of electrical stimulation:

Electrical Stimulation Acronyms




Sample conditions


(motor effect)

neuromuscular electrical stimulation


activation of skeletal muscle for strengthening

Measure: manual muscle test or dynamometry

Post-operative joint repair or replacement

Muscle is innervated


(motor effect)

Functional electrical stimulation

activation of skeletal muscle for reactivation or movement training and recovery of purposeful movement

Test or measure: functional task performance

Post-stroke, spinal cord injury or other paralytic conditions

Peripheral nerve innervation is intact


(sensory and circulation effect)

Transcutaneous nerve stimulation

applied over skin for pain modulation

referred to as "conventional", "sensory" or "high frequency"

Low back pain; neck pain


(motor and circulation effect)

Transcutaneous nerve stimulation


Twitch motor response applied to affected areas related to the pain

referred to as "acupuncture" or "low frequency"

Generalized pain


(edema reduction effect)

High Volt Pulsed Current

Applied to joints and limbs to reduce acute swelling. The active electrode is the cathode (-) in acute stages

Acute ligament sprain


(tissue repair)

High Volt Pulsed Current

Applied to wound in the inflammation and proliferation stages; changes in cell membrane and influx of calcium ions promotes tissue healing

early stages of healing: cathode (-) is treatment electrode

debridement stages (e.g. remodeling): anode (+) is the treatment electrode

Decubitus ulcers; pressure injury


Naming can be confusing! To recap, you may hear or read any of the following terms about electrical stimulation applications:

Russian, HVPC, IFC, Microcurrent, NMES, FES, or TENS

In order for therapists to reproduce the effect of electrical stimulation, best practice is to make decisions based on the waveform (e.g., DC, AC, burst or modulated AC, low intensity direct current), pulse frequency, and pulse duration


Treatment - Clinical Application

Approximately 6 minutes

When selecting electrical stimulation, a therapist must select a device and an application that will support achieving the desired effect. Common goals that may be achieved with including electrical stimulation into the treatment include:

Application Decision-Making 

The physical therapist will screen each patient for contraindications. Precautions are conditions to consider when selecting and applying electrical stimulation




There are times when a Physical Therapist may decide to use a modality that is normally contraindicated after discussion with the patient's physician. For example, a patient with a history of cancer in the distant past or application of the modality at an extremity away from the cancer site may not pose more risk than benefit.

 Estim Parameters

Electrical stimulation parameters are intentionally selected to produce the desired effect. Electrical stimulation parameters are frequency, duty cycle, ramp time, and duration. For direct current and monophasic pulsed current, the active electrode is set for a positive or negative tissue charge.

Frequency - number of electrical pulses delivered to the body in one second




<= 1 kHz



IFC, Russian, LIDC




Duty Cycle - percentage of on time to total time between pulses


Ramp Time - the time it takes to increase wave amplitude to its peak amplitude


F-08-20 Ramp.jpg










Duration - the total time providing electrical stimulation. Treatment times can range from 10 to 45+ minutes


This table provides a summary of conditions that may be treated effectively with electrical stimulation.

Key point: You will find variations in the literature about parameters with respect to pulse frequency, pulse duration, and duration. For this reason, you will not be teste on pulse frequency or pulse duration or duration. In clinical practice, you will consult the literature and use observation, patient feedback, and measures to inform your effectiveness.




Pulse Frequency (pps)

Pulse Duration (µS)



Muscle strengthening


AC, Russian




to 60&-70& max voluntary contraction

10-20 strong contractions

Contraction for function


AC, Russian




to the desired effect

task specific

Pain Modulation

High frequency TENS

pulsed AC or DC

>50; generally 80-110


to perception of stimulus; no motor response

20-30+ minutes


Low frequency TENS

pulsed AC or DC


> 150

to point of visible muscle twitch

20-45 minutes



DC or pulsed DC

(High) 100

(Low) 1-5

250. up to 1 second

to highest tolerated painful stimulus

30-60 seconds each area

Edema Management (acute)

Sensory stim

pulsed DC



to comfortable sensory threshold; just below motor response

20-45+ minutes

Edema Management (subacute/chronic)


AC, Russian



to tetanic muscle contraction

3 seconds on: 3 seconds off x 10-20 minutes


Electrodes - Material and Care

 There are many choices of electrode shape, size, and configuration to fit the need of the patient and therapeutic goal for electrical stimulation.

Types of Electrodes


Electrode Size and Current Density 

Completing the Circuit - an electrical stimulation treatment must include a full circuit. To complete the circuit, there must be:

  1. A source of energy creating an electrical potential difference
  2. A conductive pathway - including electrodes, leads, and a conductive surface with good contact
    1. Cleaning the patient's skin with alcohol to remove oil and dirt before electrode application
    2. Clipping excess body hair under electrodes
    3. Minimize warming the treatment area of the body prior to stimulation so there is minimal increased resistance

Electrode Configuration

Monopolar - always two poles: cathode (-) is active and produces cell depolarization. Produces a net charge

Bipolar - two electrodes in a single circuit; each electrode alternates between positive and negative; electrodes are of equal size; no net charge is produced

Patient will feel excitatory response under both electrodes, eliciting motor response or electrode placed over motor point, other electrode over muscle belly and may be larger

Quadripolar - four electrodes in two circuits that operate independently, yet interact

Interferential, large area, pain management, sensory stimulation of larger fiber

Note: electrical stimulation units will call the circuits "channels"

Techniques for Application of Electrical Stimulation


Treatment Goal

# Leads and Electrodes




Muscle (motor) Stimulation

One channel per muscle with both electrodes on the same muscle, two leads if it Is a larger muscle or if the device has more than one head






Sensory Stimulation

One or two channels depending on the size of the area; use as many electrodes as possible to achieve the desired sensory stimulation


One channel only if two electrodes fit in the treatment area
















Tissue repair

One channel: active electrode in the treatment area and the dispersive is placed proximally to target area >12-18" away







Evidence is emerging constantly and it is important to consider both the theoretical effects and the strength of the evidence, while keeping PICO in mind. It is a best practice to consider the patient population (P), intervention (I), comparison group (C) and outcomes (O) when making decisions about evidence-guided practice.


Clinical Decision Making and Role of the PTA


The PTA is given a Physical Therapy evaluation with patient medical history, diagnosis, goals, and plan of care (POC). Often, simply 'modalities' or 'electrical stimulation' is listed but no specific treatment parameters. Based on this information and subjective information gathered from the patient at the time of treatment, the PTA determines the most appropriate modality and parameters for that specific treatment as it falls within the POC. PTAs should also consider evidence and make evidence-guided decisions.

Patient response to treatment is always monitored and reported back to the PT. It is the responsibility of the PTA to make modifications within the plan of care and consult with the PT as needed. Since there is an object or substance being applied to the body, remember skin checks before and after application of any modality.

Communication with the patient is crucial, including informed consent, and checking for changes in the patient's medical history since the last visit. There may have been a medical test, appointment with a physician, or changes in physician's orders since the previous therapy appointment. The PTA must decide if and how the changes may affect the impending treatment and communicate with appropriate staff.

Refer to Table 10-8 in your Dutton text "Key Points to Remember When Using Electrotherapeutic Modalities"


End of Lesson