Foundations of Electrical Stimulation
PTA 101 Introduction to Clinical Practice

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.


Contact for permission




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 the characteristics of electricity and its use in rehabilitation. By understanding how different wave forms effect muscle and nerve function, we can safely and effectively select a variety of electrical stimulation options 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.
  3. Describe procedures for administering electrical stimulation, including informed consent.
  4. Describe expected goals and outcomes for application of electrical stimulation.
  5. Identify the role of the PTA during application of electrical stimulation.
  6. Discuss how the patients's age and medical status may influence selection and outcome of treatment.




Therapeutic Goals


There are several Types of Electrical Stimulation covered in Behrens text:

Type of Electrical Stimulation


Electrical Muscle Stimulation (EMS)

stimulation of denervated muscle to maintain viability

Electrical Stimulation for Tissue Repair (ESTR)

stimulation for edema reduction, increased circulation, and wound management

Neuromuscular Electrical Stimulation (NMES)

stimulation of innervated muscle to restore function including muscle strength, reduction of spasm/spasticity, prevention of atrophy, increase ROM, and muscle reeducation

Functional Electrical Stimulation (FES)

neural implantation for long term muscle activation to perform functional activities

Transcutaneus Electrical Nerve Stimulation (TENS)

portable, superficial stimulation across the skin for pain management

Characteristics of Electricity and Current Flow

To safely and effectively apply electrical stimulation to the human body, it is importance to understand the characteristics of electricity and current flow.

Key Terms: Charge = Strength

Current = Rate of Flow

Voltage = Driving Force

Resistance or Impendence = opposition

Ohm's Law Ohm's

Law defines the relationship between electrical current, voltage, and resistance. Current = Voltage/Resistance

F-08-01 ohms law.jpg





Biological tissues such as nerve and muscle membrane have the ability to simultaneously store and electric charge and oppose change in current flow. This characteristic is called capacitance. Skin and adipose act as resistors, or oppose current slow. Current always takes the "path of least resistance" when faced with multiple resistors.


Current will flow under 2 conditions:

  1. There is an energy source creating a difference in electrical potential
  2. There is a conducting pathway between the two potentials


Ionic Flow occurs in the body because like charges REPEL and opposite charges ATTRACT.


F-08-02 current flow.jpg

Anode = positive (+) electrode

Anion = negative (-) ion


Cathode = negative (-) electrode, often referred to as"active" electrode

Cation = positive (+) ion


Note the names are paired by attraction


At rest, a nerve holds a positive charge on the inside and negative on the outside.


F-08-03 ionic flow.jpg



Chemical reactions that occur under each electrode (Brethren Figures 8-2 and 8-3)


Cathode: positive Nan+ sodium ions migrate to the negative pole and combine with water to form Nao sodium hydroxide Base = increased alkalinity, promotes liquification of protein, and tissue softening

Anode: negative chlorine (Cl-) ions migrate to the positive pole and combine with water to form hydrochloric acid (HCL) = increased acidity, promotes coagulation of protein, and hardening of tissues.


Circulation improves as the body attempts to balance back to homeostasis and neutral pH level.









Impedance, or resistance to current flow, and conductivity is influenced by:


Impedance should be minimized as much as possible in order to use the lowest intensity for patient comfort. Impendence can be reduced by:

  1. Cleaning the patient's skin with alcohol to remove oil and dirt before electrode application
  2. Clipping excess body hair under electrodes
  3. Warming the treatment area of the body prior to stimulation



Constant Current vs. Constant Voltage Stimulator

Constant Current Stimulators produce a contant current independent of resistance encountered. The voltage adjusts to maintain constant current flow. The advantage of this type of of stimulator is to ensure a consistency physiologic response during the treatment. The negative is potential pain when the voltage increases to overcome resistance.

Constant Voltage Stimulators, conversely, produce a constant voltage. The current adjusts to depending on changes in resistance. This unit is advantageous in preventing discomfort with changes in resistance, such as an electrode losing full contact, but quality of response can be decreased with these automatic resistance changes.

Current Classification

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

  1. Direct Current (DC) or Galvanic
  2. Alternating Current (AC)
  3. Pulsed Current (pulsed)


According to the Behrens text, "Waveform is a visual representation of the pulse. Waveforms are diagrammatic only and rarely reflect what is actually going into the patient."

Classification of Waveforms

  1. Monophasic - single phase, unidirectional pulse from baseline to either positive OR negative
  2. Biphasic - two phase, bidirectional wave with one positive phase and one negative phase.
  3. Polyphasic - bidirectional wave with three or more phases in bursts


F-08-06 pulsed waveforms.jpg

Clinical Considerations

Waveform Comfort


Waveform Selection

Clinical Levels of Stimulation and Vacabulary

It is important to know the vocabulary listing in the and goal of these levels.

Behrens Table 8-3

Clinical Levels of Stimulation


No nerve fiber activation

No sensory awareness


Tingling, prickling, or pins and needles

Cutaneous A-beta nerve fiber activation


Strong paresthesias

Muscle contraction

A-alpha nerve fiber activation


Strong, uncomfortable paresthesias

Strong muscle contraction

Sharp or burning pain sensation

A-delta and C-fiber activation

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

Duty Cycle - ratio of on time to off time






F-08-20 Ramp.jpg

Ramp Time - gradual increase in amplitude over time from zero to peak amplitude.

Accommodation - nerve cell will not generate an action potential after a period of time, no longer responding to electrical current, without an increase in intensity. Modulation, or varying one or more parameter, can prevent adaptation to the stimulus.



Electrical Stimulation Motor Unit Recruitment

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

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

Treatment - Clinical Application






There are times clinically 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.

Procedure, Safety, and Documentation for electrical stimulation will be covered in lab

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

Techniques for Application of Electrical Stimulation

Table 9-1 Channel Set Up and Lead Management

Treatment Goal

# Leads and Electrodes




Muscle (motor) Stimulation

One lead 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 leads depending on the size of the area; use as many electrodes as possible to sensory stimulation


One lead if only one lead and two electrodes fit in the treatment area


One lead with one electrode at the spinal nerve root and the other in the sensory area














Delivery of Medication

One lead and one electrode in the treatment area and the other more proximally placed on soft tissue




Table 9-2 in the Behrens text had information regarding Potential Causes and Remedies for Patient Complaints of Prickling and itching Sensation Underneath the Electrodes.

Terminology for Configuration of Electrode Set Up

  1. Monopolar - single electrode from one channel

  2. Bipolar - two electrodes from one channel, usually equal size and shape
  3. Quadpolar - electrodes from 2 or more channels, each lead with 2 electrodes


Application Guidelines - this will be covered in depth in lab, along with the Electrical Stimulation Decision Making Tree on page 159 in your Behren's text.




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. 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.







Test Your Knowledge - Self Assessments

 Toggle open/close quiz question

 Toggle open/close quiz question 

 Toggle open/close quiz question

 Toggle open/close quiz question

 Toggle open/close quiz question

 Toggle open/close quiz question


End of Lesson


Consider using the "Why Do I Need to Know About..." and "Patient Perspective" boxes in your textbook to understand the concepts presented. Discussion questions and Case Studies are a great way to check your level of understanding. Use the CAN YOU HELP ME forum to share your thoughts with classmates.