Low Frequency
and Medium
Frequency
Currents
OBJECTIVES

Review on the difference
between high, medium, and
low medium frequency
currents and their
therapeutic/clinical
implications
OBJECTIVES

Be familiar with terms used in
electrotherapy current
modulations particularly with
WAVEFORM, (electric) PULSE,
FREQUENCY, CURRENT
INTENSITY, PULSE DURATION
OBJECTIVES
Enumerate the characteristics
of the three types of
low/medium frequency
currents
 Formulate guidelines in the
selection and/or prescription
of the most appropriate
(low/medium frequency
current) electrical modality

OBJECTIVES
Describe the basic design
features of electrical
stimulators
 Be familiar with the clinical
importance of the design
features of electrical
stimulators

OBJECTIVES
Identify the common controls
present on electrical
stimulator units
 Be familiar with the
parameters regulated by each
control present on the
electrical stimulator units

A review on the
differences…
High Frequency
Currents
Medium Frequency
Currents
Low Frequency Currents
HIGH FREQUENCY
CURRENTS
Frequency is >6000 Hz
 Short wavelengths (<10 mm)
 Effects occur only at
superficial structures
 General effect = HEATING
 Sample modalities:

 US,
MWD, SWD, IRR, UVR,
LASER
MEDIUM and LOW
FREQUENCY CURRENTS
Frequency ranges from 1 to
6000 Hz
 Longer wavelengths (>10
mm)
 Effects occur at deeper
structures
 General effects:

 MFC:
blocks pain
MEDIUM and LOW
FREQUENCY CURRENTS

Sample modalities:
 Electrical
stimulators,
Diadynamics, Biofeedback,
Iontophoresis, TENS, IT
Definition of some relevant
terms…
ELECTRIC PULSE
PULSE DURATION
CURRENT INTENSITY
WAVEFORM
FREQUENCY
ELECTRIC PULSE
A unit of stimulating current
 Otherwise known as a PHASE
(current phase)

ELECTRIC PULSE

Can be more fully described
according to DURATION (pulse
duration expressed in
seconds), INTENSITY (current
intensity expressed in
amperes or volts), and SHAPE
(waveform)
PULSE DURATION
Amount of time needed for the
rise and fall pattern to occur
at a given pulse
 Expressed in SECONDS
(millisecond=ms)

CURRENT INTENSITY
Rate of flow of electrons
 Usually expressed in AMPERES
(milliamperes = mA)

WAVEFORM
Describes the rise-and-fall
pattern of a pulse
 The shape of the waveform
reflects the time required for
the current to reach the
maximum intensity

WAVEFORM
Waveforms with sudden rise in
intensity are suitable for
innervated muscle
 Waveforms with slowly rising
intensity are best suited for
denervated muscle

FREQUENCY
Rate of change of an
electrical pulse
 Expressed in HERTZ (Hz)

Therapeutic/Clinical
Uses…
MEDIUM and LOW
FREQUENCY CURRENTS
MEDIUM and LOW
FREQUENCY CURRENTS
Assists in functional training
 Assists in muscle force
generation and contraction
 Decreases unwanted muscle
activity
 Increases rate of healing of
open wounds and soft tissues

MEDIUM and LOW
FREQUENCY CURRENTS
Helps maintain muscle
integrity after surgery
 Modulates and/or decreases
pain
 Decreases or eliminates soft
tissue swelling, inflammation,
or restriction

TYPES OF MEDIUM-LOW
FREQUENCY CURRENTS
Direct Currents
Alternating Currents
Pulsed Currents
Noted Characteristics…

QUANTITATIVE:
 Frequency (Hz)
 Pulse duration
Noted Characteristics…

QUALITATIVE:
 Number of PHASES
 Shape and symmetry of
WAVEFORMS
 Other qualitative
characteristics
Direct Current

Refers to a current passing
continuously in the same
direction (unidirectional
current)
Direct Current (cont.)
Synonyms:
 Constant Current
 Galvanic Current /
Galvanism
 Galvanic stimulation is useful
only for stimulating
denervated muscles
Direct Current (cont.)
Interrupted Direct Current
(IDC) is used to stimulate
innervated muscles
 Direct current is also used in
IONTOPHORESIS

Direct Current (cont.)
2 Types of IDC:
1. Long Duration IDC
 > 1 ms
 For sensory and motor
nerve stimulation
(denervated)
Direct Current (cont.)
2.
Short duration IDC (FaradicType)

< 1 ms

For pain control and nerve
stimulation (innervated)
Direct Current (cont.)
Physiological effects:
 Sensory stimulation
 Hyperemia
 Electrotonus
 Relief of pain
 Acceleration of healing
 Tissue destruction
Alternating Current

Defined as continuous or
uninterrupted bidirectional
flow of charged particles
Alternating Current (cont.)
2 Types:
1. Sinusoidal Current
 Evenly alternating sine
wave currents of 50 Hz
 For pain relief, edema, and
improvement of circulation
Alternating Current (cont.)
2.
Diadynamic Current

Rectified monophasic
sinusoidal current

For pain relief, tissue
healing, muscle reeducation and
improvement of circulation
Pulsed Current

Defined as the uni- or bidirectional flow of charged
particles that periodically
ceases for a finite period of
time
Pulsed Current (cont.)
Types:
1. Symmetrical Biphasic
2. Balanced Asymmetrical
Biphasic
3. Unbalanced Asymmetrical
Biphasic
4. Monophasic
GUIDELINES…
Selecting, Prescribing,
or Purchasing the MOST
APPROPRIATE
Electromodality
GUIDELINES…
Determine your treatment
goals
 Note for the presence of
contraindications


Determine the usual
conditions of or problems
presented by patients of the
facility/area
GUIDELINES…
Consider the market
availability of the modality
and its cost
 Consider the requirements for
maintenance of the modality

BASIC DESIGN FEATURES
and CONTROLS…
Electrical Stimulators
BASIC DESIGN FEATURES
Path from power source to the
unit (plugs and cables)
 Control knobs and/or buttons
 Electrodes (with cables)

Alternative power source
 Safety features

BASIC DESIGN FEATURES

Controls or adjustment
knobs/buttons for:
 Frequency
 Intensity
 Mode (continuous or pulsed)
Pulse Duration and Intervals
 Treatment Duration

Basic Electrode Systems
1.
2.
3.
Malleable metal
electrodes
Electrodes that conform
to the body surfaces
Water Bath
Malleable Metal Electrodes
Made of tinplate or aluminum
with pad of lint, cotton gauze
or sponge at the end
 Pad/gauze/sponge is wet with
water before being applied to
skin
 Electrodes kept in place with
bandages / straps

Malleable Metal Electrodes
(cont.)

If unequal in size, the smaller
electrode is active & most
effects will occur here; the
other electrode is the
indifferent or dispersive
electrode
Electrodes that Conforms to
the Body Surface
Made of carbon-impregnated
silicone rubber
 Used with sponge pads or
thin layer of conducting gel
 Kept in place with strap or
adhesive tape

Electrodes that Conforms to the
Body Surface
Less efficient in passing
current than metal electrodes
 Has lower impedance than
polymer electrodes

Water Bath
Used for hand, forearm, foot
and leg which is placed
between the electrodes
 Provides a large area for the
indifferent electrode & for
applying muscle stimulating
currents
 Current density depends on
location of electrodes

Methods of Electrode
Placement
1.
2.
3.
UNIPOLAR
BIPOLAR
QUARDRIPOLAR
Unipolar Motor Point
Stimulation
One small active electrode &
one large dispersive
electrode
 Site of stimulation: motor
point for stronger response

Unipolar Motor Point
Stimulation
Same amount of current
passes thru each electrode
 Smaller sized electrode has
higher current density
(stronger effect)

Unipolar Motor Point
Stimulation (cont.)
Used for innervated and
denervated muscles
Indications:

 Peripheral
nerve injuries
 Tendon transplants
Unipolar Motor Point
Stimulation (cont.)
Contraindications:
 Cases
wherein active
motion is prohibited
 Patients with
pacemakers
 Directly over superficial
metal implants
Unipolar Motor Point
Stimulation (cont.)
Contraindications:
 Active
bleeding over
treatment site
 Malignancies over
treatment site
Unipolar Motor Point
Stimulation (cont.)
Precautions:
 Sensory
loss over
treatment site
 Open wounds
 Extreme edema
Bipolar Motor Point
Stimulation
Equally sized electrodes
 Effect of stimulation is
dependent on electrode
placement
 Current density is equal in
both electrodes
 Effective for stimulating
muscle groups or very large
muscles

Bipolar Motor Point Stimulation
(cont.)
 Used for innervated and
denervated muscles
Indications:
 Peripheral nerve injuries
 Inhibition of muscle activity
due to joint pain and
effusion
Bipolar Motor Point Stimulation
(cont.)
Indications (cont.):
 UMN lesions to decrease
spasticity & facilitate active
contraction
 Disuse atrophy
 Immobilization
 Orthopedic & neurological
cases with LOM
Bipolar Motor Point Stimulation
(cont.)
Contraindications &
Precautions:
 Same as Unipolar
application
Quadripolar Motor Point
Stimulation
Electrodes from two or more
circuits positioned so that
currents geometrically
intersect
 Used for Interferential
Stimulation Technique (MFC)

Quadripolar Motor Point
Stimulation (cont.)
Indications:
 Pain & muscle spasm
 Edema
 Hematoma
 Chronic ligamentous
lesions
 Urinary stress incontinence
Quadripolar Motor Point
Stimulation (cont.)
Contraindications &
Precautions:
 Same as Unipolar
application
Importance of Stimulation
Parameters

The effect of electrical
stimulation on the tissue
will depend on the rate of
change of the electrical
pulse:
1. No change / Slow change
in electric pulse
 IONTOPHORESIS /
DIRECT CURRENT
Importance of Stimulation
Parameters (cont.)
2.
3.
Very fast change of rate

HIGH FREQUENCY
CURRENTS
Rate of change between
nos. 1 & 2

LOW & MEDIUM
FREQUENCY CURRENTS
Importance of Stimulation
Parameters (cont.)

The current intensity determines
the extent of physiological
changes
 When stimulating a muscle at a
constant frequency the only way
to increase the force produced
is to recruit more motor units by
increasing the intensity of
stimulation
Importance of Stimulation
Parameters (cont.)

A single pulse is described by
their:
1.
Duration

2.
Intensity

3.
Seconds / Milliseconds /
Microseconds
Milliamps / Volts
Shape

Illustrates the change of
intensity with time
Importance of Stimulation
Parameters (cont.)

The relationship between time
and current intensity is the
rate of change in current
Current used in Galvanic current
and Iontophoresis
Current used for Nerve
Stimulation
Current used for producing
Single Nerve Impulse
Current used for TENS & Faradic
Stimulators
Surged current producing
Muscle Contraction
Current Flow in the Tissues
The quantity of current that
flows in the tissues and the
path it follows will depend on
the impedance of that
pathway
 Generally, watery tissue such
as blood, muscle and nerve
has low ohmic resistance

Current Flow in the Tissues
(cont.)
Bone and fat has higher ohmic
resistance
 The epidermis has the highest
ohmic resistance, which is
determined by:

 Thickness
& nature of skin
 Inter-electrode distance
Current Flow in the Tissues
(cont.)
This electrical resistance can
be reduced by:
 Washing & wetting the
surface
 Warming the skin
Skin Irritation as an Adverse
Response
Skin irritation may be caused
by:
 Electrical
reaction
 Electrochemical
response
 Allergic response to
electrodes, gel, or tape
Skin Irritation as an Adverse
Response (cont.)
Skin irritation may be caused
by:
 Mechanical
irritation
caused by shearing forces
between adhesive
substances and the skin
Hazards in Electrotherapy
Chemical damage due to
inadequate skin protection
when direct or interrupted
current is used
 Disruption of stimulating
devices due to proximity of
diathermy output
 Skin irritation
 Electric shock

Contraindications to
Electrical Stimulation
Strong muscle contraction
might cause joint/muscle
damage; detachment of
thrombus; spread of infection;
and hemorrhage
 Stimulation of autonomic
nerves might cause altered
cardiac rhythm or other
autonomic effects

Contraindications (cont.)
Currents might be unduly
localized due to open wounds
or skin lesions
 Currents might provoke
undesirable metabolic
activity in neoplasms or in
healed tuberculous infections

Contraindications (cont.)

Current is not evenly phasic,
leading to possible skin
damage or irritation,
especially if there is loss of
sensation
Principles of Application
Conduct general safety
checks with respect to the
equipment
 Check the patient for
contraindications
 Explain the treatment fully to
the patient

Principles of Application (cont.)

Collect the necessary
equipment
 ES, electrodes, wiring
 Soap & water for cleaning
the skin
 Contact gel / sponge, tape /
straps / Velcro
Principles of Application (cont.)
Position the patient in the
comfortable position
 The skin should be uncovered
& examined for any
contraindications to
treatment
 Test the equipment as
appropriate; demonstrate the
technique to the patient

Principles of Application (cont.)
Wash the skin over the region
of electrode contact. Soaking
the skin for 3-4 min either in
a bath or with a warm, damp
pad may reduce skin
resistance
 Select appropriate treatment
parameters

Principles of Application (cont.)
Always turn all intensity dials
to zero before beginning the
treatment
 Place the electrodes as
appropriate for the treatment

Principles of Application (cont.)
Increase intensity until
desired result is produced
 Never lift the active electrode
from the skin or replace it
without turning the intensity
to zero

Principles of Application (cont.)
Terminate the treatment;
check the skin condition
 Keep a full record of the
treatment
