This document discusses interferential therapy (IFT), including its history, principles, instrumentation, applications, effects, and precautions. Some key points: - IFT was developed in the 1950s and involves applying two medium frequency alternating currents slightly out of phase to produce a low frequency effect for therapeutic purposes. - The interference of the currents produces an amplitude-modulated frequency that can stimulate tissues in a manner similar to low frequency electrotherapy. - IFT is used for pain relief, muscle stimulation, increasing blood flow, and reducing edema through its physiological effects on tissues from 10-150 Hz. - Proper electrode placement and current parameters are important to achieve the intended effects while avoiding contraindic

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DEFINITION
Developed by Dr. Hans Nemec of Vienna,
Austria in the early 1950’s
It may be described as the transcutaneous
application of alternating medium
frequency electrical currents, amplitude
modulated at low frequency for therapeutic
purposes.
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Why IFT?..
MF currents associated with a lower skin resistance
(impedance),
more comfortable than low frequency currents
more tolerable penetration of current through the skin
is possible
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SKIN IMPEDANCE
The word impedance comes from the Latin impedire
meaning to prevent, to stop from going on.
Impedance signifies the resistance of a conductor
when an electric current passes.
Conventionally speaking, the term resistance refers
to the obstacle to the direct current, and it is
represented by the letter R.
The terms impedance refers to the obstacle to the
alternating current and it is represented by the
letter Z.
Impedance Z, as resistance R, is expressed in ohms.
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SKIN IMPEDANCE
SKIN IMPEDANCE is calculated as Z = ½ π f C
Where,
Z = skin resistance
f = frequency in Hertz (Hz)
C = capacitance of skin in microfarads
From above formula, skin impedance is inversely
proportional to frequency and capacitance of the
skin.
Capacitance of the skin cannot be changed; hence by
increasing the frequency the skin impedance can be
lowered.
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SKIN IMPEDANCE
It is assumed that a capacitance of 1 microfarad.
For a 50-Hz alternating current we obtain:
Z = 1/2π x 50x 10-6 = 3200 Ω
For a 4,000-Hz alternating current this means:
Z = 1/2π x 4000x 10-6 = 39,8 Ω
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PRINCIPLE
The principle of IFT is to pass two Medium
Frequency Alternating Currents which are
slightly out of phase, through the tissues,
where the currents intersect to produce a
low frequency effect.
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Principles of wave interference: Combined Effects
Constructive, Destructive, & Continuous
Constructive interference: when two sinusoidal waves
that are exactly in phase or one, two or three
wavelengths out of phase, the waves supplement each
other in constructive interference
+
=
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Principles of wave interference: Combined Effects
Destructive interference: when the two waves are
different by 1/2 a wavelength (of any multiple) the
result is cancellation of both waves
+ =
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Principles of wave interference: Combined Effects
Continuous Interference: Two waves slightly out of
phase collide and form a single wave with progressively
increasing and decreasing amplitude
=
+
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WORKING
In the interferential therapy method, two medium-
frequency alternating currents that interact with each
other are used.
One of the alternating currents has a fixed frequency
of 4,000 Hz while the frequency of the other
alternating current can be set between 4,000 and 4,250
Hz.
The superimposition of one alternating current on the
other is called interference
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WORKING
The frequency of the new medium-frequency
alternating current can be calculated as follows:
f1 + f2 /2 where
Example:
f1 = 4,000 Hz
f2 = 4,150Hz
f1 + 1/2Δf = 4,000 + 75 = 4,075 Hz (Resultant Carrying
Frequency)
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WORKING
The frequency with which the amplitude varies is
referred to as the amplitude modulation frequency
(AMF).
In interferential therapy the AMF (treatment
frequency) corresponds to frequencies which are used
in low-frequency electrotherapy.
The AMF has a value of f1 – f2
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WORKING
The AMF has a value of f1 – f2
Example:
f1 = 4,000 Hz
f2 = 4,150 Hz
f 1 - f2 = 4,000 - 4,150 = 150 Hz (AMF or treatment
frequency)
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Amplitude Modulation Frequency
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4000 Hz
4150 Hz
150 Hz

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4000 Hz
3900 Hz

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Why Amplitude modulation?
Synchronous depolarization
Asynchronous depolarization
Gildemeister effect/summation principle
Wedensky inhibition
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SWEEP
The principle of using the sweep is that the machine is
set to automatically vary the effective stimulation
frequency using either pre-set or user set sweep ranges.
Such sweep prevents accommodation of nerves.
Example:
An AMF of 20 Hz is set and a 50 Hz spectrum is added.
The current begins with an AMF of 20 Hz and passes
successively through all frequencies up to 70 Hz, after
which it decreases gradually to 20 Hz.
This process is repeated automatically.
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Triangular sweep pattern Rectangular Sweep Pattern
Trapezoidal Sweep Pattern 21

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Vector Scan
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INSTRUMENTATION
AMF PARAMETER To choose the basic value of the LF
modulation that is desired.
SPECTRUM PARAMETER to set the range of variation in
the AMF value that is desired; for ex. AMF at 100Hz and
spectrum at 50Hz will give an AMF variation from 100hz up
to 150Hz and back to 100Hz.
SWEEP TIME PARAMETER sets the time period for the
AMF to change from base to peak frequency. Faster sweep
is used for less painful stimulation and for strong muscle
contraction or sensory input, sweep must be slow, to ensure
aggressive stimulation.
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INSTRUMENTATION…
CONTOUR PARAMETER sets the rate of change
of the AMF from the base to peak frequency.
ROTATION PARAMETER is applicable in case of
vector currents only and sets the rate of rotation
and the direction change of the AMF field within
the tissues.
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APPLICATION
Methods of applications are:
1. Static interference
2. Dynamic interference
3. Bipolar interference
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STATIC INTERFERENCE
Here the area in
which IFT is set up
remains stationary.
This area of static
interference gives an
appearance of
‘clover leaf ’.
It lies to 45°angles
to the perpendicular
lines from each
electrode.
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DYNAMIC INTERFERENCE
This is moving the area
of interference current in
a to and fro manner
through 45°.
It is obtained by varying
the current intensity
from 50 to 100%.
The dynamic area of
interference is also called
as vector sweep, vector
scan, rotating vector, etc.
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BIPOLAR INTERFERENCE
Here pre-modulated IFT
are applied through 2
surface electrodes.
IFT is generated inside
the equipment and is
delivered to the patient
through 2 electrodes.
Useful for smaller areas.
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PHYSIOLOGICAL EFFECTS
This depends upon:
1. Magnitude of current
2. Type of mode used i.e. Rhythmic or
constant
3. The frequency range used
4. Accuracy of electrode positioning
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PHYSIO.EFFECTS (CONT…)
Main clinical applications are :
1. Pain relief
2. Muscle stimulation
3. Increased local blood flow
4. Reduction of edema
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PAIN RELIEF
Believed that this may be achieved by
stimulation of the reticular formation at
frequencies of 10-25Hz or by blocking ‘c’
fiber transmission at > 50Hz.
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MUSCLE STIMULATION
For patients who can not generate useful
voluntary contraction, IFT may be
beneficial.
Most effective motor nerve stimulation
range is between 10-25Hz
When employing IFT it is possible to
continue to stimulate the muscle beyond its
point of fatigue. Some machines employ a
‘surged’ mode to overcome this.
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BLOOD FLOW
Experimentation demonstrated vascular
changes at 10-25Hz.
Effects of blood flow is believed to be due to:
1. Effects of suction electrodes on tissues
2. Effects of muscle stimulation on circulation.
3. Deep tissue penetration stimulates
parasympathetic nerve fibers for increased
blood flow.
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OEDEMA
Local muscle contraction combined with its
local vascular changes encourages the
reabsorbtion of tissue fluid.
The use of suction electrodes may also be
beneficial.
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CONTRAINDICATIONS
1. Cardiac pacemaker
2. Advanced cardiac disease
3. Hypertension
4. Thrombosis
5. Hemorrhage
6. Pregnancy
7. Neoplasm
8. T b
9. Fever
10. Infections
11. The eyes
12. Skin disorders
13. Epiphyseal region in children
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PRECAUTIONS
IFT apparatus must be at least 6 meters
away from SWD machine
Patients with febrile conditions
Epileptic patients
Over anterior chest wall
Position suction electrode below the level of
damage or discomfort.
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Placement of electrodes
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Types of Electrodes
Plate
Vacuum
Pen
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Plate Electrodes
Made of conducting rubber which are
comfortable and long lasting
larger plates electrodes give more comfortable
treatment and deeper effect
Smaller electrodes are used for a localized
effect, but this effect is more superficial
Attached to the patient by means of straps to
assure a good contact and greater tolerance of
treatment

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Vacuum Electrodes
made from a vacuum unit plug into a rubber suction
cup connected to a machine capable of producing a
vacuum,
suction should not be constant because it can be
uncomfortable and causes bruising
wet sponges are placed in the cups and moisten the
edges of the cups for better adherence,
excellent for treating flat smooth areas for example
back or a plump knee
not indicated for treatment of the hairy areas because
can’t get an airtight seal

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Electrode positioning
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ELBOW
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KNEE
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NECK
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SHOULDER
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LOWER BACK
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Thank You