Interferential therapy is a form of electrical stimulation that uses two medium frequency currents between 4000-5100 Hz to generate low frequency interference currents between 1-100 Hz at targeted tissue depths. This allows for pain relief, muscle stimulation, increased blood flow and lymphatic drainage without the limitation of skin resistance. Electrodes are placed diagonally over the area of interest and current intensity is gradually increased until felt by the patient. Contraindications include coagulation issues, arterial disease, infections and pacemakers. Typical applications are for pain, swelling, muscle stimulation and tissue healing.

1. Interferential therapy
Module Teacher
Ehsanur Rahman
BscPT. MScPT (DU)
Associate Professor, PT Dept, BHPI
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

2. History
It may be described as the transcutaneous application of alternating
medium frequency electrical currents; amplitude modulated a low
frequency for therapeutic purposes.
Introduced in 1905’s by Hans Nemec in Vienna.
Interferential therapy uses two medium frequency currents around 4000
Hz to evoke interference currents between 1 & 100 Hz.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

3. Definition
• Interferential therapy is a form of electrical treatment in which two
medium frequency currents are used to produce a low frequency effect
at any tissue depth without the problem of skin resistance.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

4. Principle of IFT
• Interferential therapy is a method of producing low frequency alternating
currents selectively at any tissue depth, without the problem of skin
resistance, & stimulate nerve & muscle.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

5. Skin resistance
• Medium frequency currents, associated with a relatively lower skin
resistance, are believed generally to be more comfortable than low-
frequency currents; thus using a medium frequency , a more tolerable
penetration of current through the skin is possible.
• The following equation describe the relationship between frequency &
impedance –
• Z = 1/ 2FC,
• Where, Z = impedance in Ohms, F = frequency in Hz & C = capacity of
the skin in microfarads.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

6. Amplitude modulation/ the interference effect
 Amplitude modulation is a term used to describe the transmission of an
information – containing signal by varying the amplitude of a carrier wave.
 When two differing unmodulated medium frequency alternating
currents are applied simultaneously to the tissue, through a paired
electrodes, a vibration is generated in the tissue where the currents
cross , the intensity of the combined currents will increases & decreases
rhythmically. This is called interference effect.
 The combined current has a beat frequency which is the difference
between, also known as a amplitude modulation frequency & it is this
which triggers the nerve & muscle impulse.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

7. Amplitude modulation/ the
interference effect cont..
In interferential therapy units one
circuit is kept constant at one
frequency & a beat frequency can
be selected by altering the
frequency of the second circuit.
e.g – if one circuit is 4000 Hz & a
beat frequency of 50Hz is required,
the 2nd circuit is selected at 4050Hz.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

8. Production of IFT
 IFT generator is equipped with two oscillator circuit which produce a
fixed frequency in one circuit & a variable frequency in the other
circuit. Frequency ranges from 4000 Hz – 5100Hz.
 The medium frequency currents are applied to the tissue by means of
a pair electrodes for each circuit, using a quadripolar technique, placed
perpendicularly to each other.
 The electrodes are positioned so that the area where the two current
cross each other, is directly over the lesion.
 Most machine allow for a constant beat frequency to be selected
(constant mode). It is also possible to rhythmically & regularly change
the beat frequency over a specific period of time = frequency
modulation/ sweep/ swing.
 The frequency using continuously, changing the frequencies from the
lower value to the higher value. To prevent accommodation of nerve.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

9. Production of IFT cont..
• Rotating vector – vary the
strength of the current
relative to each other. The
interference pattern will
rotate to an angle of 45° in
each direction to ensure
that a wide area can be
covered by interferential
current.
• If the site of lesion cannot
be localized, than rotating
vector is selected.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

10. Physiological effects of IFT
• The physiological effects on tissue depends on the
following factors -
Frequency
Mode – constant/ rhythmic
Intensity of current used
Position of electrode
Patency of circulation & neurological function.
• 100 Hz constant –
a) Vasodilatation
b) Heat production
c) Alter ion distribution locally
d) Relieve pain. Ehsanur Rahman
Associate Professor, MPT Co-ordinator

11. Physiological effects of IFT cont…
• 1 to 10 Hz constant –
a) Effect on motor nerve & cause muscle contraction
b) Stimulate only innervated muscle
c) Mobilize tissue ion
• 1 to 100 Hz rhythmic –
a) Facilitate ion movement in the cell.
b) Relaxation of muscle
c) Hyperaemia
d) Increase venous & lymphatic flow
e) Reduce oedema
f) Facilitate tissue healing.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

12. Physiological effects of IFT cont…
• 90 to 100 Hz rhythmic –
a) Analgesic effect
b) Vasodilatation
c) Effective for migraine & brachial neuralgia.
• 1 to 10 Hz rhythmic –
a) Effect on motor nerve & tissue
b) Vasodilatation.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

13. Therapeutic effects
Relief of pain: Interferential currents are frequently employed for
pain relief.
A placebo effect: Since Interferential machines are technically
impressive and produces a pleasant effect, so there is a placebo
effect by this therapy.
Muscle contraction: Muscle contraction can also be achieved at
higher current amplitude. Strong muscle contractions can be
achieved without any significantly uncomfortable skin resolution.
Control of swelling: As muscle contraction happens in
interferential therapy, the muscle contraction can control swelling
and oedema.
Treatment of stress incontinence: After pelvic floor exercise,
interferential therapy is very useful in case of treatment of stress
incontinence.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

14. Indication
• Pain –
• by stimulating of Aβ fiber.
• There is no fixed frequency for different condition, but a guide
line is
i. 100Hz – activation of pain gate mechanism
ii. 10 to 25 Hz – encephalin & endorphin release by stimulation of
Aδ & C finer.
iii. 50Hz – temporary physiological block of finely myelinated/ non
myelinated nociceptive fiber. Most comfortable.
iv. 10 to 150Hz – parasympathetic stimulation – increase blood
flow, remove chemical irritant & decrease edema.
v. 0 to 5 Hz – sympathetic stimulation – increase blood flow,
remove chemical irritant & decrease oedema.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

15. Indication cont..
• Oedema – increase venous & lymphatic flow, aiding the absorption
of exudation.
• Muscle stimulation – muscle contraction. Useful for deep muscle &
stress incontinence.
• Tissue healing – as it effect cellular activity.
• Muscle Spasm - Electrokinesy currents have been used effectively
for muscle spasm.
• Heamatoma – During the first 24 hours, 200 Hz constant, together
with ice pack interferential therapy is useful for the resolution of
heamatoma.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

16. Application of IFT
• Machine setting –
Setting for frequency – beat frequency/ variable beat
frequency/ time for variable beat frequency.
Intensity – as intensity increases the patient will feel a tingling
sensation.
Sensory effect is gained at 4 – 10 mA.
Motor effect is gained at 8 – 15 mA.
Setting for rotating vector – on/off..
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

17. Application of IFT cont…
• Electrode placement –
4 electrodes, 2 for each circuit.
Carbon rubber or metal electrode.
Placed over a damp sponge for good skin contact.
Attached to the body with strap.
Electrode are placed diagonally each other, so that 2
currents will interfere in the correct area.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

18. Method of application
• Patient preparation –
• Explanation – nature of treatment
• Feeling of treatment.
• Suitable comfortable position.
• Wash the skin with warm soapy water to decrease skin resistance.
• Place the electrode.
• Switch on the machine, select all setting. Frequency, intensity,
rotating vector, time.
• Gradually increase the intensity, until it can be felt by patient.
• It is necessary to increase the intensity periodically as
accommodation will occur.
• After completion of treatment remove the pad & check the skin.
Ehsanur Rahman Associate Professor, MPT Co-ordinator

19. Contraindication
 Anti coagulant therapy - within last three month. Risk
of haemmorrahing.
 Arterial disease.
 Deep vein thrombosis – the thrombi may dislodge.
 Infective condition.
 Pregnant uterus/ during menstruation.
 Malignant tumor.
 Pace maker.
 Open wound. Skin lesion.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

20. Dosage
• The intensity depends on following factors-
I. Frequency – Higher frequency less sensitive and lower frequency high
sensitive.
II. Size of electrodes – The smaller the electrode, the greater the
concentration of current.
III. Duration – The sensation reduces after a few minutes.
• The intensity is not determined by the machine it is determined by
the patient’s reaction. The intensity is divided into following types –
i. Low dose – not noticeable by the patient.
ii. Medium dose – just noticeable
iii. High dose - a vigorous pleasant sensation
iv. Very high dose – strong, vigorous, almost unpleasant sensation.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

21. Advantages
• Large doses of interferential current can be given without the fear
of producing a chemical burn and surface discomfort.
• Decreased skin sensation is not a contra-indication to treatment,
as the patient’s deep sensation and the meter on the unit are
satisfactory guide.
• The current can be localized more effectively in a specific area by
careful positioning of the electrodes. Lesions at any depth and in
an extensive area can be treated.
• Metal is not a contra indication. There are a number of problems
of pain and swelling in patients with metal implants which can be
eased effectively by interferential currents.
• Referred pain can be effectively treated in some cancer patients.
Ehsanur Rahman
Associate Professor, MPT Co-ordinator

22. Ehsanur Rahman
Associate Professor, MPT Co-ordinator