This document provides information about electromyography (EMG). EMG is a test that evaluates the health and function of muscles and the nerve cells that control them. It involves inserting a needle electrode into a muscle to record electrical activity from muscle fibers and nerves. Abnormal spontaneous electrical activities in muscles can indicate neurological or muscular disorders. EMG is useful for diagnosing conditions like amyotrophic lateral sclerosis, myasthenia gravis, and muscular dystrophy. It provides information about the location and severity of nerve or muscle damage.

1. ELECTROMYOGRAPHY
-Batul Dawoodi (MPTh musculoskeletal disorders)
-Guided by: Dr. Kairavi Trivedi (PhD Scholar)

2. ELECTRODIAGNOSIS
• Electrodiagnosis is a method of obtaining information about diseases
by passively recording the electrical activity of body parts or by
measuring their response to external electrical stimulus.
• It measures the electrical activity of nerve (cause and extent of nerve
damage) and muscle.

3. Benefits of testing
• Correlating with physical examination
• Definitive diagnosis in nerve/muscle disorders
• Localisation of lesion
• Determination of physiological status of lesion
• Data for clinical or lab research
• Regeneration status of nerve
• Temporal parameters: acute, subacute, chronic

4. Goals
localization
muscle
Fibre type
Pathology
Temporal course
Neuromuscular
junction (NMJ)
Nerve Anterior Horn cell
severity

5. ANATOMY OF MUSCLE
• SKELETAL MUSCLE

6. • MUSCLE FIBRE

8. ELECTROMYOGRAPHY
• Electromyography refers to
recording of action potentials
of muscle fibers firing singly or
in groups near the needle
electrode in a muscle
• The muscle action potential
when recorded by a needle
appears triphasic as the action
potential approaches, crosses
and leaves the recording
electrode.

9. • Recording from an area incapable of
propagating the impulse, therefore,
results in large positivity with a low
and long negativity.

10. USES
MEDICAL RESEARCH:
1:ORTHOPEDIC
2:SURGERY
3:FUNTIONAL NEUROLOGY
4:GAIT AND POSTURAL ANALYSIS
REHABILITATION:
1:POST SURGICAL
2:NEURO-REHABILITATION
ERGONOMICS:
1:ANALYSIS OF DEMAND
2:RISK PREVENTION
3:ERGONOMIC DESIGN
4:PRODUCT CERTIFICATION
SPORTS SCIENCES:
1:BIOMECHANICS
2:MOVEMENT ANALYSIS
3:ATHLETIC STRENGTH TRAINING
4:SPORTS REHABILITATION
BIOFEEDBACK

11. RELATIVE CONTRAINDICATIONS
1. Coagulopathy
2. Risk of infection
3. Chest or abdominal area- risk of pneumothorax or peritoneal
insertion

12. Instrumentation
Stimulator/
electrodes
Patient Electrodes Preamplifier Amplifier
Display
(visual and
sound)
Input Phase Processing phase(amplified *1000 times)
Processing phase Output phase

13. TYPES OF EMG
NEEDLE
ELECTRODES
NEEDLE
ELECTRODE
CONCENTRIC MONOPOLAR SINGLE FIBRE MACROELECTRODE
BIPOLAR
ELECTRODE
SURFACE
ELECTRODE

14. Monopolar electrode
• Made of stainless steel
• Very finely sharpened point
• Covered with Teflon or other insulating material (except for a 0.5 mm
exposure at the tip).
• The needle serves as the active electrode, and a surface electrode
placed on the skin close to it serves as a reference.

15. • ADVANTAGE:
• patients accept them better because they are of small diameter and Teflon
covering allows them to slide in and out of the muscle easily.
• DISADVANTAGES:
• With repeated use, the size of the bare tip changes, thereby limiting the
number of examinations for which that needle can be used.
• The Teflon peels back, exposing a larger area that then changes the recorded
characteristics of the motor unit potentials.
• Because the active electrode tip and the surface electrode are separated by
some distance, the background noise becomes much greater as remote
muscle contractions may be picked up easier.

16. CONCENTRIC ELECTRODE
• It consists of a cannula with an
insulated wire (or wires) down the
middle.
• The active electrode is the small tip of
the center wire, and the reference
electrode is the outside cannula.

17. • ADVANTAGES:
• Because the active and reference electrodes are closer together, using
the concentric electrode minimizes background noise.
• The electrode picks up motor units from only a very small distance.
• No (reference) surface electrode is needed.
• DISADVANTAGES:
• On comparison with other needles, its larger diameter can cause more
pain, and moving the electrode around is uncomfortable.

18. BIPOLAR NEEDLE ELECTRODE
Concentric needles may have two
central wires (bipolar), in which case
the active and reference electrodes
are at the tip and the outside cannula
acts as the ground.

20. SINGLE FIBER NEEDLE ELECTRODE
• Used for special studies, this needle consists of a 0.5-0.6 mm stainless
steel cannula with a 25 µm fine platinum wire inside its hollow shaft.
In a side port 3 mm behind its tip, the cut end of the platinum wire is
exposed.
• Used in diagnosis of myasthenia gravis and NMJ disorders

21. SURFACE ELECTRODES
• Because they can pick up gross motor unit activities, the evaluation of
single motor unit potentials with surface electrodes is difficult. They
are best used as reference electrodes when monopolar needles are
used.
• They can also be used however, in kinesiology to obtain gross
indications about muscle activity and in gait analysis.

22. SIGNAL PROCESSING COMPONENTS
• When electrical potential differences are recorded in response to activating
excitable tissue, the voltage changes are generally too small to be
immediately visualized on common display devices
• The amplitudes of biological electrical signals recorded from nerve and
muscle are in the range of several microvolts to a few millivolts.
• Adequate display of the responses requires some signal processing by other
electronic devices such as
1. Amplifiers
2. Filters
3. Signal averages
4. Integrators
5. analog-to-digital converters

23. 1. Amplifiers:
• It increases the amplitude of electrical voltages monitored in electrophysiological
examination.
• Such devices are used to make small electrical signals larger on signal display
instruments
• In some cases when low-voltage signals are being monitored, the amplifier built
into the display device increases the signal size enough for accurate measurements.
• A feature characteristic of all amplifiers is the device's gain.
• If the peak voltage of a monophasic input signal is doubled from I mV to 2 mV, the
gain of the amplifier is two.
• Amplifiers used in electrophysiological examination should uniformly increase
signal size for all signals within a specified frequency range (or bandwidth) from 2
to 10 Hz to 10,000 Hz.

25. Amplifiers
Simple Differential

26. • 2. Filters:
• Physiological responses of nerves and muscles have characteristic frequency ranges.
• The "noise" of the external environment can be electronically removed from the excitable
tissue signal (as long as the frequency ranges do not overlap) by an electronic device
called a filter.
• Several types of bandpass filters are commonly found on modern electrophysiological
testing instruments.
1. Notch filter: 60-Hz AC line noise can be eliminated from higher frequency signals by
using a notch filter. This type of filter can be set to reject signals at 60 Hz and pass (or
keep) a band of frequencies both less than and greater than 60 Hz.
2. Low frequency filter: It filters out the low-frequency signals (like those associated
with movement of the electrode) and passes (keeps) the higher frequency signals (this
type of filter is also known as a high pass filter).
3. High-frequency filter: (also known as a low pass filter), rejects higher frequencies
and passes the lower frequency signals.
• The low- and high frequency filters of ENMG devices are generally adjusted to 2 to 10
Hz to 10,000 Hz for motor nerve conduction studies, 10 Hz to 10,000 Hz for needle
electromyography, and 2 to 30 Hz to 2000 Hz for sensory nerve conduction studies.

27. • 3. Signal averagers:
• If a single response to an electrical stimulus is very small, and the electrical noise
recorded from the environment is large, visualization of the electrical signal of interest
may not be immediately possible.
• To overcome this problem of an important electrical signal being buried in noise, signal
averaging was developed.
• In signal averaging, an electrical stimulus is applied to evoke electrical activity in an
excitable tissue. For a short period of time following the stimulus, all electrical activity
(voltage changes) from the tissue is recorded and stored.
• When a second stimulus is applied, the electrical response is again stored and
electronically added to the record from the first stimulus.
• This process is repeated, with each successive record being added to the sum of all
previous records.
• Because the elicited potentials are time locked to the stimulus and reoccur at a fixed time
after the stimulus, signal averaging will enhance these signals.
• Electrical interference (noise) is not time locked to the stimulus, and the averaged noise
voltage transients will be eliminated by the average
• The signal averaging technique is used to record sensory nerve action potentials and
somatosensory evoked potentials.

28. • 4. Integrators:
• Integration of an electrical signal is the calculation of the area under a
signal waveform or curve.
• The units of the output of an electronic integrator are volts-seconds.

29. 5. Analog to digital converters:
• For many clinical applications, the physiologic electrical responses from
nerve or muscle are recorded, processed (e.g., amplified and filtered),
and displayed as an analog output.
• This is the form of the output signal displayed on strip charts and many
oscilloscopes and stored on FM tape recorders.

30. • Display and storage devices:
• An electrical response of excitable tissue can be displayed in analog
(continuous) or digital form (discrete or digitized measurements).
• An entire waveform may be displayed on an oscilloscope, computer
screen, or a strip chart recorder (polygraph).
• An entire event or series of events may be preserved for future analysis
on an FM tape recorder (analog data) or in computer memory (digitized
data). Both of these data storage methods allow further analysis.

31. CROSS TALK
• An undesired EMG signal from a muscle group that is not commonly
monitored is called “crosstalk”
• Crosstalk contaminates the signal and can cause an incorrect interpretation of
the signal information.
• Crosstalk depends on the many physiological parameters and can be
minimized by choosing electrode size and inter-electrode distances (typically
1–2 cm or the radius of the electrode) carefully.
• Crosstalk increases with increasing subcutaneous fat thickness.
• Minimal crosstalk area (MCA) is defined as a surface where crosstalk versus
co-contraction of muscles is minimal. The precise location and measurements
of the distance between two bony landmarks are the keys to finding the
“minimal crosstalk area” of the targeted muscle. MCA helps to limit or avoid
crosstalk from neighboring muscles

32. Steps for performing EMG
1. Select the muscle as per the suspected clinical diagnosis- proximal muscles in
myopathy, both distal and proximal muscles supplied by different roots and nerves in
motor neuron disease and the specific muscles innervated by the suspected nerve or
radicular involvement
2. Instruct the patient how to contract and relax the muscles
3. Identify the muscle while the patient is contracting and relaxing the muscle
4. Locate the needle insertion point slightly away from the motor point to prevent end
plate noise.
5. Insert the needle quickly while the muscle is relaxed to minimize the pain.
6. Sharp MUP’s on minimal contraction confirm that the needle is in proper position. If
MUPs are not sharp, needle should be repositioned.

33. Recording
technique
Insertional activity
Spontaneous
activity
Normal
spontaneous
activity originating
from NMJ or
terminal axon
Abnormal
spontaneous
activity originating
from muscle fibre
Fibrillations
Positive sharp waves
Myotonic discharges
Complex repetitive
discharges
Abnormal
spontaneous
activities from
motor neuron or
axon
1.Fasciculations
2.Doublets, triplets and
multiplets
3.Myokymic discharges
4.Neuromyotonia
5.Cramp potentials
Voluntary activity
Minimal voluntary
contraction
Maximal voluntary
contraction

34. INSERTIONALACTIVITY
• Introduction of the needle into the muscle normally produces a brief
burst of electrical activity due to mechanical damage by needle
movement and it lasts slightly exceeding the needle movement
• Duration: 50-200 ms
• It appears as positive or negative high frequency spike in a cluster

35. Insertional activity
Normal Decreased
In chronic cases where
very few viable muscle
fibers are left
Eg: Fibrosis
Increased
Prolonged
In acute cases when
membrane stability is
compromised
Absent
Complete chronic
denervation

37. • THE MUSCLE AT REST:
• Following cessation of insertional activity, a normal relaxed muscle
will exhibit electrical silence which is the absence of electrical
potentials
• It is often difficult for the patient to completely relax sufficiently to
observe complete electrical silence

38. SPONTANEOUS ACTIVITY
• Normal spontaneous activity originating from NMJ or terminal axon:
• Once the insertion activity decays after a second in normal individuals,
there is spontaneous electrical activity.
• In the end plate zone however miniature end plate potentials are
spontaneously recorded.
• The end plate potentials are usually seen with an irregular baseline and
called as end plate noise. In the end plate region, action potentials which
are brief, rapid, and irregular with an initial negative deflection are known
as end plate spike.
• Sound: sputtering fat in a frying pan.
• Endplate spikes are due to mechanical activation of nerve terminals by the
needle. To avoid the normally occurring spontaneous and plate activities,
the needle should be introduced slightly away the motor point.

41. • Miniature end plate potentials:
• Miniature end plate potentials are the small (~0.4mV) depolarizations of the
postsynaptic terminal caused by the release of a single vesicle into the
synaptic cleft.
• Neurotransmitter vesicles containing acetylcholine collide spontaneously
with the nerve terminal and release acetylcholine into the neuromuscular
junction even without a signal from the axon.
• These small depolarizations are not enough to reach threshold and so an
action potential in the postsynaptic membrane does not occur.
• During experimentation with MEPPs, it was noticed that often spontaneous
action potentials would occur, called end plate spikes in normal striated
muscle without any stimulus.
• Sound: sea shell heard near to ear
• Sellin LC, Molgo J, Thornquist K, Hansson B, Thesleff S (1996). "On the possible origin of giant or slow-rising miniature end plate potentials at the
neuromuscular junction". Pflügers Archiv: European Journal of Physiology. 431 (3): 325–334. doi:10.1007/BF02207269. PMID 8584425. S2CID 8748384.

42. • Abnormal spontaneous activities from muscle fiber:
1. Fibrillation:
• Fibrillation are spontaneously occurring action potentials from a single
muscle fiber.
• Frequency: 0.5 – 15 Hz
• Amplitude of 20-200 u V
• Duration of 1-5 ms when recorded by a concentric needle (Danner 1982).
• Sound: rain drop on roof
• Fibrillation are biphasic or triphasic waves with initial positivity which is
an important differentiating feature from end plate spike.

44. 2. Positive sharp waves
• long duration biphasic potentials with initial sharp positivity followed by a long duration
negative phase resulting in a saw tooth appearance.
• amplitude of 20 – 200 µ V
• Duration of 10- 30 ms.
• Sound: dull pop
• The denervated muscle fibres develop not only hypersensitivity to acetylcholine but the
number of ach receptors also increase which leads to depolarization and is responsible
for fibrillation and positive sharp waves.

46. Fibrillation and sharp waves are found in:
A. Neurogenic
• Anterior horn cell disease (ALS, SMA, Poliomyelitis)
• Radiculopathy
• Axonal neuropathy
• Plexopathy (brachial or lumbosacral)
B. Neuromuscular junction
• Botulism
• Myasthenia gravis
C. Myogenic
• Myositis
• Muscular dystrophy
• Acid maltase deficiency
• Myotubular myopathy
• Muscle trauma

47. • Fibrillations and positive sharp waves are graded as follows:
0= none
+1= persistent single train of potential (2-3 sec) in at least two areas
+2= moderate number of potentials in 3 or more areas
+3= many fibrillations or sharp waves in all areas
+4= full interference pattern of fibrillations or sharp waves

48. • Sharp waves: Seen early stage of denervation before the appearance of
fibrillation, myotonic disorders, and polymyositis and rarely in normal
individuals.
• Sharp waves are more commonly recorded with monopolar needles
compared to concentric ones.
• The mechanisms responsible for sharp waves are:
• Distant recording from fibrillating fibres
• Different degrees of membrane instability. (Sharp waves probably appear at a
lesser degree of membrane instability.)

50. 3. Myotonic discharges:
• The action potentials of muscle fibers firing for a prolonged period after
external excitation are the characteristics of myotonic charges.
• The action potentials wax and wane in amplitude and frequency because
of muscle membrane abnormality.
• Frequency: between 20 and 150 Hz which is regular and rhythmic.
• Sound: Dive bomber.
• Depending on the location of needle electrode to the muscle fiber, there
are 2 types of these potentials
(1) Positive wave
(2) Brief spikes

51. POSITIVE WAVES
• The positive wave are similar to
the runs of positive sharp wave
and are attributed to the injury
to the muscle fibres.
• The frequency and amplitude of
positive waves in myotonia
varies as the discharge continues
BRIEF SPIKES
• Brief spikes are biphasic or
triphasic, 20 -300 u V and
resemble the fibrillation
potentials.
• These occur after a voluntary
contraction, wax and wane
similar those induced
mechanically.
• The later discharges correspond
to the poor relaxation which is
clinically evident.

52. • Myotonic discharges are found in:
1. Myotonia dystrophica
2. Myotonia congenita
3. Paramyotonia
4. Hyperkalemic periodic paralysis
5. Polymyositis
6. Acid maltase deficiency
• Myotonic discharges may be seen with or without clinical myotonia
• It is never the dominant waveform

53. Differentiation from other wave forms
• Although morphology of myotonic discharges simulates fibrillation
and positive sharp waves, it can be differentiated from these by its
characteristic waxing and weaning whereas fibrillations and positive
sharp waves are regular

56. 4. Complex repetitive discharges (CRDs):
• Complex repetitive discharges refer to repetitive and synchronous firing of a
group of muscle fibers spontaneously or following needle movement.
• Amplitude: 50 µV to 1mv
• Morphology of all CRDs are identical from one discharge to another
• Duration:50 to100 ms.
• Frequency: 5-100 Hz.
• Sound: machine like sound
• Their unique repetitive pattern bears a superficial resemblance to myotonic
discharges and these are also called pseudomyotonic discharges.
• Complex repetitive discharges do not have a waxing and weaning
character. On the contrary these appear and disappear suddenly and this
feature helps in differentiating it from myotonic discharges

57. Ephaptic transmission

60. • CRDs are found in:
• Myogenic:
• Polymyositis
• Muscular dystrophies
• Myxoedema
• Schwartz-Jampel syndrome
• Neurogenic:
• Poliomyelitis
• Amyotrophic lateral sclerosis
• Chronic radiculopathies
• Chronic neuropathies

61. • Abnormal spontaneous activities from motor neuron or axon:
• Fasciculations:
• Fasciculation potentials are spontaneous contractions of a number of
muscle fibers belonging to whole or a part of motor unit.
• Fasciculations occur randomly and irregularly at variable rates ranging
between 1 and 500/min.
• The size and shape of fasciculations depend on the distance of
recording electrode from the motor unit.
• Fasciculations may have the appearance of normal or abnormal MUP
and can be recognized by their slower firing rare compared to MUP.

62. • Fasciculations are of two types:
1. Benign:
• Not accompanied by muscle weakness, wasting and reflex changes.
• Normal MUP morphology
• Fire at faster rate and occur at same site repetitively
2. Pathological

63. • Fasciculations are found in:
• Neurogenic disorders:
• Amyotrophic lateral sclerosis
• Spinal muscle atrophy
• Radiculopathy
• Syringomyelia
• Peripheral neuropathies
• Metabolic disorders:
• Tetany
• Thyrotoxicosis
• Anticholinesterase drugs
• Uremia
• Normal:
• Benign fasciculation
• Muscle cramps

65. • Doublets, Triplets And Multiplets:
• Spontaneous MUPs that fire in group of two, three or multiple potentials
• They originate because of spontaneous depolarisation of motor unit or
its axon similar to fasciculations
• Found in:
• Hyperventilation
• Tetany
• Motor neuron disease
• Metabolic diseases
• Ischemia can also induce doublets or multiplets

67. • Myokymic discharges:
• Spontaneous muscle potentials associated with fine, worm like quivering
of facial muscles are known as myokymic discharges.
• On EMG, these discharges reveal normal MUPs which fire in fixed
pattern and rhythm, occurring in bursts of 2-10 potentials firing at 40-60
Hz.
• The bursts recur at regular intervals of 0.1 to 10 sec creating a marching
sound.
• It appears as a result of spontaneous depolarization or ephaptic
transmission along demyelinated segment of nerve

68. • Myokymia can be differentiated from fasciculations by their distinct
pattern and different clinical significance.
• Facial Myokymia is found in
• Multiple sclerosis
• Brainstem neoplasm
• Polyradiculopathy
• Facial nerve palsy.
• Limb Myokymia is found in
• radiation plexopathy
• chronic nerve compression.

69. • Neuromyotonia:
• Neuromyotonia refers to continuous motor unit potentials firing at a
rate of 100-300 Hz which continue for long runs or recur in bursts.
• These are not influenced by voluntary activity.
• Neuromyotonia is found in syndrome of continuous muscle fiber,
activity, anticholinesterase poisoning. and spinal muscular atrophy.
• Ischemia augments or precipitates the Neuromyotonia in Tetany.
• Neuro myotonic discharges also occur in peripheral nerve lrritation
during surgery and serve as valuable guide of possible damage.

71. • Cramp potentials:
• In cramps, spontaneous discharges of potentials occur at 40-60 Hz
usually with an abrupt onset and cessation. Increasing number of
potentials are recruited as the cramp develops and drops out it subsides.
• The high frequency discharges of MUPs in cramp suggests its origin in
nerve rather than muscle
• The cramps occur in
• Salt depletion,
• Chronic neurogenic atrophy,
• Myxoedema,
• Pregnancy,
• Uremia
• Normal individuals.

74. • Motor unit potential (MUP)
• After evaluation of insertional and spontaneous activities, the next step
of EMG is evaluation of MUP on voluntary contraction.
• The basic unit of peripheral nervous system is the motor unit, which
comprises individual lower motor neuron, its axon, NMJ and muscle
fibers
• Depolarization of motor neuron to the threshold results in impulse
propagation through axon, which in turn results in excitation of all
muscle fibers more or less simultaneously supplied by that motor
neuron in normal situation
• Recruitment of MUPs refers to additional firing of MUPs during
muscle contraction which depends on size principle.

75. • Size principle:
• The size of the motor unit is dependent on size of motor neuron,
diameter of axon, thickness of myelin, conduction velocity,
depolarization threshold and metabolic type of muscle fibre
• The larger motor neuron has larger axon and thicker myelin hence
faster conduction velocity, higher threshold for depolarisation and
usually supplies type II muscle fibres which are required for fast twitch
• According to size principle, the motor neurons are recruited in order of
size from small to large (Henneman1974)

76. • In routine EMG, most MUPs analyzed are the smaller low threshold
representing type I muscle fibre
• The MUP represents the sum of the muscle action potentials supplied
by an anterior horn cell.
• The MUP therefore has a higher amplitude and longer duration than
action potential produced by a single muscle fiber.
• MUPs are assessed for their morphology, stability and firing pattern

77. • Amplitude, duration, number of phases, rise
time, and firing rates characterize the
morphology of motor unit potential.
• Traditionally one measures the amplitude
from peak to peak
• the duration from the first deflection of the
baseline to the last return to it
• the number of phases by counting the
number of times the components of the
motor unit potential cross the baseline plus
one
• rise time as that elapsed between the peak of
the initial positive (down) deflection to the
peak of the highest negative (up) deflection.

78. • The number of fibers contained in a motor unit and their degree of synchrony
affect those characteristics.
• The number of phases a motor unit contains depends largely on the synchrony of
depolarization of its muscle fibers and can be affected either by nerve disease
causing differential slowing in impulse conduction, or muscle disease where the
conduction characteristics of the muscle fibers themselves have changed.
• The rise time, strictly a function of the proximity of the needle tip to the muscle
fibers of the contracting unit, is usually between 200 and 300 µsec.
• The firing rates of motor units depend on their type and size. Smaller units are
recruited early, with weak effort, and fire faster than large units which are
recruited later as effort is increased.
• All the above characteristics vary with age, with the muscle under study, and with
muscle temperature. Minute changes in needle position can greatly affect the
shape of the motor unit potential.
• Temperature Effect: At lower temperatures the motor unit duration and its
amplitude are increased

79. • DURATION:
• The duration of MUP is a measure
of conduction velocity, length of
muscle fiber, membrane excitability
and synchrony of different muscle
fibers of a motor unit.
• The duration of MUP, is much less
influenced by the distance of
recoding electrode compared to the
amplitude
• SOUND:
• Low frequency long duration: dull
and thud like
• High frequency short duration: crisp
and sharp

80. • RISE TIME:
• The rise time of MUP is the duration from initial positive to subsequent
negative peak.
• It is an indicator of the distance of needle electrode from the muscle
fiber.
• A slower rise time is attributed to resistance and capacitance of the
intervening tissue which acts as high frequency filter and results in a
dull sound on the loudspeaker of EMG equipment.
• This indicates the need to reposition the needle closer to the muscle
fibers.

81. • AMPLITUDE:
• The amplitude of MUP is measured peak to peak
• It depends upon size and density of muscle fibers, synchrony of firing,
proximity of needle to the muscle fiber, age of the subject, muscle
examined and muscle temperature.
• Decreasing muscle temperature results in higher amplitude and longer
duration of MUPs

82. • PHASE OF MUP:
• Motor unit potential recorded by a concentric or monopolar needle
reveals as inverted triphasic potential (Positive- negative – positive).
• The phase is defined as the portion of MUP between departure and
return to the baseline i.e. number of Baseline crossings + 1.
• It is a measure of how synchronously muscle fibers in a motor unit fire
• A motor unit potential with more than 4 phases is called as polyphasic
potentials.
• Some potentials show directional changes without crossing the
baseline and these are known as turns.
• Polyphasia and turns suggest de-synchronisation or drop out of muscle
fibres.

83. Normal motor unit parameters
• Amplitude: 200 µV-5 Mv
• Duration:5-15 ms
• Rise time:100-200 μs (<500 μs)
• Frequency: 5-15/s (<60/s)
*Measured from initial positive peak to negative peak for triphasic
potentials

84. • Satellite potential:
• Satellite potentials are the
late potentials which are
time – locked to the main
motor unit potential.
• Seen in early innervation

85. • STABILITY OF MUP:
• Normally, if the needle electrode is fixed, there is no variation in the MUP
morphology of an individual motor unit.
• Variation in MUP is is a feature of abnormal NMJ transmission

86. VOLUNTARY CONTRACTION OF MUSCLE
• FIRING PATTERN OF MUP:
• On initiation of voluntary contraction of muscle, the motor units are
recruited in an orderly manner; the smallest appearing first, larger ones
later and the largest still later.
• It is based on size principle
• Key points to study firing pattern is activation and recruitment.
• Activation denotes the firing rate and is dependent on central mechanism
• Recruitment refers to the ability to recruit new MUPs as the firing rate
increases

87. EVALUATION OF MUP
• The classic method of MUP measurement is the isolation and
recording of at least 20 individual potentials and then measuring their
duration, phases, turns and amplitude which compared with the control
values for the muscle for the corresponding age.

89. ABNORMALITIES OF MUP
1. Short duration MUPs
2. Long duration MUPs
3. Polyphasic MUPs
4. Mixed pattern

90. 1. SHORT DURATION MOTOR UNIT POTENTIALS (MUPS):
• The short duration MUPs are those with a duration shorter than for the
muscle of corresponding age.
• Short duration MUPs are usually of low amplitude and have rapid
recruitment at minimal effort
• The short duration MUPs are found in the disorders associated with loss
OR segmentation of muscle fibres.
• Short duration MUPs that found in
• myopathies and neuromuscular junction disorders
• early stage of reinnervation after nerve damage.
• In certain myopathies such as metabolic and endocrine, only a few or no short
duration MUPs are recorded.

91. 2. LONG DURATION MUPs:
• The duration of MUPs if exceeds the normal value for the corresponding
muscle and age, constitutes the long duration MUPs.
• The long duration MUPs are generally associated with high amplitude and
poor recruitment; but sometimes the amplitude may be normal or low.
• Long duration MUPs are seen in
• motor neuron disease
• axonal neuropathies with collateral sprouting
• Chronic radiculopathies
• chronic Myositis such as polymyositis and inclusion body Myositis.
• The long duration MUPs are attributed to increase in fiber density. loss of
synchrony of firing of muscle fibres and increase in number of muscle fibres
in a motor unit.

93. 3. POLYPHASIC MUP:
• Polyphasic MUPs are diagnosed when there are 4 or more phases in a
MUP.
• The individual components of a polyphasic potential represent the action
potentials recorded from a single muscle fiber.
• These are most frequently seen in myopathies where there is regeneration
of fibers and increased fiber density.
• Regeneration of axons in neurogenic diseases can also result in polyphasic
MUPs.
• If MUP is large, an increase in fiber density results in more turns without
extra phases, such a MUP is called complex MUP and it may be found in
any myopathy or neurogenic atrophy.
• Some polyphasic potentials may have very late satellite potential which is
known as linked potential or parasite potential. This makes the MUP
duration very long.

94. 4. MIXED PATTERN:
• Occasionally instead of a polar from of short or long duration MUPs, a
mixed variety, comprising of short, long and polyphasic MUPs is
found.
• This pattern may be found in both myopathies and neurogenic
abnormalities.

95. Maximal voluntary contraction
• INTERFERENCE:
• During strong voluntary contraction, normally there is a dense pattern
of multiple superimposed potentials which is called as interference
pattern.
• Less dense pattern may occur with a loss of motor units, poor effort
and upper motor neuron lesions or a strong muscle.