Electrical Stimulation Principles

What is Electrical Stimulation?

- involves the passing of current through the skin via electrodes

How can electricity be delivered?

- an electrode can either deliver electricity to the muscle (ex. high volt) or record electrical activity of the muscle (ex. biofeedback)

What does a LEAD do?

- connects electrodes to the electrical stimulation machines

What do ELECTRODES do?

- connect with the leads and are attached to the pt.'s skin near target tissues

How can you decrease HOT SPOTS?

- if you decrease skin resistance, you decrease the resistance to the flow of electrical current
- size of electrode is selected based on size of Rx. area
- closely spaced electrodes will result in more superficial stimulation
- electrodes spaced further

What are the (3) types of e-stim?

- Carbon Impregnated electrodes: rubber electrodes; reusable, need dampened sponge
- Self- Adhering electrodes: can sometimes be reused (on same pt.)
- Metal electrodes

What does the DISPERSIVE PAD do?

- completes the circuit, current travels back to the machine
- size must be greater that the sum of the active electrodes


- the amount of current concentrated under an electrode

What is the relationship between current density and electrode size?

- inverse relationship of current density to electrode size
< more concentrated current density with smaller electrode size
< less concentrated current density with larger electrode size
- that is why the smaller active electrode (if using direct current/

What are the possible reasons for a pt. describing prickling/biting sensation under the electrode?

- electrode has poor contact with tissue
- electrode has hot spots: current is not evenly distributed across electrode
- high resistance between electrode and tissue
< irritated skin, dry flaking skin, oil/lotion on skin
< dried out interface between the

What is the MONOPOLAR electrode set-up?

- single smaller active electrode on Rx. area
- larger dispersive electrode placed on the SAME side of body as Rx. site
- current will be felt mostly under the smaller active electrode
- 1 complete electrical circuit

What is the BIPOLAR electrode set-up?

- 2 electrodes of equal size on Rx. area from 1 channel of current
- current will be felt equally under both electrodes
- 1 complete circuit

What is the QUADRIPOLAR electrode set-up?

- 2 sets of 2 equal size electrodes
- 2 complete electrical circuits, therefore requires 2 channels of current
- Usually all 4 electrodes are the same size
- Circuits often set up parallel to each other, DONT CROSS the currents (exception- interferential)

What is DC- Direct Current?

- Galvanic Current
- electrons flow continuously uninterrupted in one direction
- active electrode is either positive or negative
- polarity does not change, so current does not return back to the baseline unit it is off

What is AC- Alternating Current

-direction of electron flow changes from positive to negative in a cycle
- each electrode becomes positive for 1/2 cycle, then negative for 1/2 cycle
- polarity changes so wave moves above and below the baseline in a rhythmical manner

What is CURRENT? (I)

- how fast free electrons flow = rate of flow
-measured in ampere (A)
- ex. how many people are are getting through the hallway at once

Define Voltage (V)

- the difference in electrical charge creates a force that pushes the charge, causing the flow of electricity from one place to another
- electrons move from are of high concentration (more neg.) to an area of low concentration (less negativity)

Define Resistance (R)

- determines the ease/difficulty of current moving through substances
- measured in Ohms
- in biological tissue, resistance is called impedance

What is Conductance?

- the ease of current movement
- a good conductor has low resistance
- an insulator has high resistance
< conductors: nerve & muscle
< insulators: skin, adipose, bone

Conductance within the Body

- electrical current takes the path of least resistance, once past the skin and subcutaneous tissue
- if there is more water content in a tissue, the water will increase the conductance (decreases resistance/impedance), therefore current will flow more ea

Ohm's Law

Current = voltage/resistance

Ohm's law relationship

- increase in voltage will increase current (R is constant)
- increased resistance will decrease current (constant V)

Characteristics of Flow: Cathode

- negative active electrode
- attracts (+) charged ions called car ions
- positive ions (cat ions), migrate toward negative cathode

Characteristics of Flow: Anode

- positive active electrode
- attracts (-) charged ions, called an ions
- negative ions (an ions) migrate toward positive electrode (anode)

Pulsed Current

- stop the flow of electrons for a period of less than 1 second

Monophasic Pulsed Current

- is direct current (either positive or negative)
- wave moves above baseline when on and down to baseline when off
- only 1 phase

Biphasic Pulsed Current

- is alternating current (alternates between pos. and neg.)
- wave moves above baseline then below baseline, then to baseline when off
- waveforms may or may not be symmetrical

Polyphasic Pulsed Current

- a burst groups together a finite series of pulses delivered to the body as a single charge

What is Amplitude

- peak-amplitude: the maximum current or voltage delivered in one phase of a pulse
- determines the strength of the stimulation
- amplitude can be sub sensory, sensory, motor, or noxious
- measured in current (mill amperes (mA); or microamperes (uA), or (

Rise Time

-how long it takes to increase from zero to peak amplitude

Decay Time

- how long it takes for the peak amplitude to decrease back down to zero

Pulse Duration

- from start to finish, how much time 1 complete pulse takes
- usually the shorter the pulse, the less resistance the current will have entering the tissue

Interpulse Interval

- time of rest between each complete pulse

Phase Duration

- time from beginning to end of one pause of a pulse (AC)
- comfort decreases as phase duration increases

Intrapulse Interval

- time between phases of a complete pulse
- short rest period before the alternating current goes from pos. to neg. during one total AC pulse

Pulse Frequency

pulse rate or pulses per second (ops) = pulse rate
- # of pulses delivered to the body in 1 second
- fatigue is greater at higher frequencies because there is less time between pulses

How the body responds to the pulse rate/freq.

1-15 pps = distinct contraction with each pulse
15-30 pps = transition to a smoother contraction (usually will feel pulsation)
35-50 pps = smooth, tetanizing (total) contraction of a muscle

Duty Cycle

- on/off time
1/3 = 10 sec ON / 30 sec OFF
1/5 = 10 sec ON / 50 sec OFF

How does duty cycle affect treatment duration?

- the longer the OFF time, the less fatigue
- 1/3 -- 15 min Rx. time
- 1/5 -- 30 min Rx. time

Ramp Time

- how long it takes for current to go from 0 to peak amplitude and how long it takes to return to 0
- associated with comfort of the stimulation (.5-1 sec for comfort)
- too fast of a rise in amplitude is uncomfortable


- modifying any of the electrical parameters during the delivery of stim
- modulation can increase pt. comfort and decrease a pt.'s accommodation to current


- usually the goal is for a contraction of the muscle
- recruitment of enough motor units to have a smooth contraction
- as one increases the intensity, pt.'s discomfort also increases
- keep intensity as low as possible while still accomplishing the goal

Electrode Placement

- place longitudinally along muscle fibers (more conductive)
- place at proximal and distal end of muscle belly
- the closer the electrodes are to one another, the more superficial the stim -- keep further apart
- certain areas have less resistance so les


- transcutaneous electrical stimulation
- E stim to the skin to decrease pain (sensory, sometimes motor)


- electrical muscle stimulation using Direct Current
- E stim to Denervated muscle to maintain muscle viability


- neuromuscular electrical stimulation (alternating current)
- stimulation of Innervated muscle to restore muscle function
- used for muscle strengthening, reduction of muscle spasm, prevention of muscle atrophy, and muscle reeducation


- functional electrical stimulation (AC)
- activates Innervated muscle with the goal of the muscle performing functional activity or exercise
- NMES and FES often used interchangeably


- High Volt Pulsed (Galvanic) Stimulation
- paired, unidirectional (pulsed DC) impulses that rise and fall quickly (= short rise time and short decay time), with high voltage
- used mostly for would healing or to control acute edema


- Interferential Current
- involves crossing the pathways of 2 waves of different frequencies for pt. comfort


- sub sensory type of electrical stimulation


- Iontophoresis
- ion transfer, used to introduce medications into the tissues using DC

How does pain travel?

- sensations travel as nerve impulses along specific sensory fiber pathways to the spinal cord, up the spinothalamic tract, to the brainstem, to the thalamus (relay station), and up to the somatosensory portion of the cerebral cortex
- information regardi

Gate Theory of Pain Control

- sensory info fibers all meets up at the attachment to the grey matter of the spinal cord
- at that point there is a "gate keeper" a connecting inhibitory interneuron to both the pain fibers (C fibers) and general sensory fibers (A- beta fibers)
- if bot

Endogenous Opiates

- naturally occurring substances in the body which can inhibit neurotransmission of impulses of the pain fibers and yet not affect the transmission of touch or proprioception sensory impulses


- produced in the pituitary gland
- vigorous exercise for 30-40 min. can stimulate release
- also can be released with meditation or acupuncture
- long lasting effect -- 4-8 hours


- stimulated by non painful sensory stimulus
- present when sensory stimulus present
- lasts for very short duration after stimulus ends