Interferential therapy involves applying two medium frequency alternating currents intersecting in the body to produce a low frequency interference current. This current is able to penetrate deeper into tissues than direct current, allowing for pain relief and muscle stimulation. The interference current is modulated to create a beat frequency effect. Different electrode types and application methods exist to target specific areas. Physiological effects include reducing pain, increasing blood flow and muscle stimulation. Treatment parameters like frequency, duration and method of application are chosen based on the condition and treatment goals.

1. INTERFERENTIAL CURRENTS

2. • Medium frequency currents are the currents
whose frequency falls between the range of
1000 to 10,000 Hz.
• They are being used therapeutically due to
their advantage of greater penetration and
with a higher tolerance and comfort over the
low frequency current.

3. INTRODUCTION
• The principles of Interferential Therapy were first
introduced by Ho Nemec(an Austrian scientist).
• Interferential currents are also known as Nemec’s
currents. In this two medium frequency currents
are used to produce a low frequency current
effect.
• It may be described as the transcutaneous
application of alternating medium frequency
electrical currents, amplitude modulated at low
frequency for therapeutic purposes

4. • Since direct application of faradic current results in
pain due to high impedance of tissues, so to have a low
frequency effect two medium frequency currents are
used.
• Out of these two medium frequency currents one
current is usually of 4000Hz because there is minimum
impedance generated by the tissues against this
frequency current.
• The other current can be varied accordingly

5. SKIN IMPEDENCE
• 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

6. • SKIN IMPEDANCE is calculated as
Z = 1⁄2 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

7. PRINCIPLE
• The principle of IFT is to pass two Medium Frequency
Alternating Currents through the tissues, where the
currents intersect to produce a low frequency effect

8. • The Interferential therapy depends upon the
principles of Interferential effect of two medium
frequency currents crossing in the patient’s
tissues.
• The interference produced by two currents in the
tissues is called the beat frequency which is also
referred to as Amplitude Modulation Frequency
• For example let us take to medium frequency
currents, current in circuit A = 4,000 Hz and
circuit B = 4150Hz

12. • Thus it is possible to produce any desired
frequency in the range of 1-250 Hz by varying
the frequency difference of the carrier
currents
• One of the major advantages by the use of
interferential therapy is that the effects are
produced in the tissues where they are
required, without unnecessary or
uncomfortable skin stimulation

13. • The advantage of IFT is that it can be used for
pain relief as well as for muscle stimulation
• The principle of reduction in pain is because of
gate control theory and stimulated release of
pain reducing substances (endorphine and
enkephalin)

14. 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

15. Triangular sweep pattern

16. ELECTRODES
Pad/Plate electrodes Adhesive electrodes Vacuum electrodes

17. Plate/Pad 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

18. 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

19. • Suction electrodes are seen to be much more beneficial as it
is useful in delivering the currents in uneven surfaces
• Carbon pad electrodes are the most commonly used
electrodes and are easier to apply

20. METHODS OF APPLICATION
• There are 3 different ways of applying IFT
1. Bipolar interference
2. Static interference
3. Dynamic interference

21. 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

22. 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.

23. 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.

25. PHYSIOLOGICAL EFFECTS

26. Main clinical applications are :
• Pain relief
• Muscle stimulation
• Increased local blood flow
• Reduction of edema
• Various specialised application – e.g. stress
incontinence

27. PAIN RELIEF
• Electrical stimulation for pain relief has
widespread clinical use, thought the direct
research evidence for the use of IFT in this role is
limited.
• Logically one could use the higher frequencies
(90-130Hz) to stimulate the pain gate
mechanisms & thereby mask the pain symptoms.
• Alternatively, stimulation with lower frequencies
(<5Hz) can be used to activate the opioid
mechanisms, again providing a degree of relief.

28. 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.

29. 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

30. 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.

31. MANDATORY STEPS
• RUKE NO 1: Assess the patient
• RULE NO 2: Know your equipment
• RULE NO 3: Complete the patient preparation
and machine preparation
• RULE NO 4: Choose appropriate programs
• RULE NO 5: Keep taking feedback from the
patient during the treatment
• RULE NO 6 : Cleanliness before and after

32. TREATMENT PARAMETERES
1. Method of application:
– Depends on the area being treated
– Pain pattern
2. Frequency sweep:
– Triangular - Acute
– Rectangular/Square: Sub Acute
– Trepizoidal: Chronic

33. • Duration:
– In acute conditions, shorter treatment times of 5-
10 minutes may be sufficient to achieve the effect.
– In other circumstances like chronic conditions or
long standing cases, it may be necessary to
stimulate the tissues for 20-30 minutes.

34. Contra Indications
• Cardiac pacemaker
• Advanced cardiac disease
• Hypertension
• Thrombosis
• Hemorrhage
• Pregnancy
• Neoplasm
• Fever
• Infections
• The eyes
• Skin disorders
• Epiphyseal region in children

35. 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.