1. ELECTROMYOGRAM
CHAIRPERSON :DR.AMRUTH
STUDENT :DR.ANUSHA S J

3. NERVE CONDUCTION STUDIES (NCS)
• MOTOR NERVE
CONDUCTION STUDY
• Technique
• conduction velocity (CV) as:
velocity (m/s) = distance (mm) /
(proximal latency [ms] −
distal latency [ms])
• F WAVE

4. • SENSORY NERVE
CONDUCTION STUDY
• Technique

5. • Late responses: F-waves
• 1. F-waves results from small number of motor neurons activated by
antidromic (back-firing)
• 2. Variable in amplitude and latency
• 3. Commonly minimum latency is measured
• 4.Supra maximal stimulus are applied

6. • H Reflex
• It is a true reflex (it has afferent, synaps & efferent pathway)
• Need sub maximal stimulation

9. DIABETIC NEUROPATHY

10. CARPAL TUNNEL SYNDROME

12. MOTOR UNIT

13. • WHAT IS ELECTROMYOGRAPHY (EMG)?
• Technique of recording the electrical activity of motor unit firing •
• Not muscle force per se, but the electrical signal sent by the motor nerves to
muscle fibers to create force
• The electromyogram is the trace of the electrical signal detected by the
electrode

14. INTRODUCTION
• Electromyogram (EMG) is a technique for evaluating and recording the
activation signal of muscles.
• EMG is performed by an electromyograph, which records an
electromyogram.
• Electromyograph detects the electrical potential generated by muscle cells
when these cells contract and relax
• The study of EMG’s is called electromyography

15. • Types of EMG Electrode Categories
• Inserted :Fine-wire (Intra-muscular)
Needle
• Surface

17. • Fine-wire Electrodes
• Advantages
• Extremely sensitive
• Record single muscle activity
• Access to deep musculature
• Little cross-talk concern
• Disadvantages
• Requires medical personnel, certification
• Repositioning nearly impossible
• Detection area may not be representative of entire muscle

18. • Surface Electrodes
• Advantages
• Quick, easy to apply
• No medical supervision, required certification
• Minimal discomfort
• Disadvantages
• Generally used only for superficial muscles
• No standard electrode placement
• May affect movement patterns of subject
• Limitations with recording dynamic muscle activity
• Cross-talk concerns

19. ELECTRODE PLACEMENT
• Away from tendon
• Fewer, thinner muscle fibers
• Closer to other muscle origins, insertions
• Away from outer edge of muscle
• Closer to other musculature
• Orientation parallel to muscle fibers

20. EMG PROCEDURE
• Clean the site of application of electrode;
• Insert needle/place surface electrodes at muscle belly;
• Record muscle activity at rest;
• Record muscle activity upon voluntary contraction of the muscle.

21. EMG PROCESSING

22. ELECTRICAL CHARACTERISTICS
• The electrical source is the muscle membrane potential of about -70mV.
• Measured EMG potentials range between < 50 μV up to 20 to 30 mV,
depending on the muscle under observation.
• Typical repetition rate of muscle unit firing is about 7-20 Hz.

25. TYPES OF EMG ANALYSIS
• Clinical/diagnostic using needle electrodes
• Research/movement analysis using surface or fine wire
electrodes

27. FACTORS THAT INFLUENCE THE SIGNAL
INFORMATION CONTENT OF EMG
• • INTRINSIC FACTORS:
• – Muscle fiber diameter involved in the signal
• – Number of muscle fibers involved in the signal
• – Muscle fiber conduction velocity
• – Muscle fiber type
• – Muscle fiber location

28. • – Motor unit firing rate
• – Muscle blood flow
• – Distance from the electrode to the muscle fiber
• – Amount and type of tissue surrounding the muscle
• – Hydration state of the muscle
• – Number of active motor units
• – Fatigue
• – Temperature

29. EXTRINSIC FACTORS
• – Characteristics of the electrode-skin interface
• – Inter-Electrode spacing
• – Ambient noise
• • Power line hum
• • Machinery
• • Cross – talk (signals from sources other than what is studied)
• – Distance between the electrode and the motor point

30. CONTRA INDICATION OF NCS & EMG
• 1- Patient with artificial peacemaker
• 2- Patient with bleeding disorder

32. In a practical sense, electrodiagnostic testing can be considered in any of the
following circumstances, when a patient is complaining of or has:
1. numbness
2. tingling (parenthesis)
3. pain
4. weakness
5. a limp
6. Muscle atrophy
7. Depressed deep tendon reflexes
8. Fatigue
The entire procedure takes approximately 30 to 60 minutes and causes only mild
side effects that may include bruising and tenderness at the electrode site.

39. EMG APPLICATIONS
• Disorders of nerve
• Disorders NMJ
• Disorders of muscle

41. CONCLUSION
• The electrodiagnostic (EDX) examination is an extension of the clinical neurologic
examination
• a) The bioelectric potential associated with muscle activity constitute the
electromyogram (EMG).
• b) Muscle is organized functionally on the basis of the motor unit.
• c) A motor unit is defined as one motor neuron and all of the muscle fibers it
innervates.
• d) When a motor unit fires, the impulse (action potential) is carried down the motor
neuron to the muscle. The area where the nerve contacts the muscle is called the
neuromuscular junction, or the motor end plate.
• e) The potentials are measured at the surface of the body, near a muscle of interest or
directly from the muscle by penetrating the skin with needle electrodes.
• f) EMG potentials range between less than 50 μV and up to 20 to 30 mV, depending
on the muscle under observation.
•

42. REFERENCES
• HARRISON’S PRINCIPLES OF INTERNAL MEDICINE 20TH EDITION
• Instrumentation and Neurophysiology :Sanjeev D. Nandedkar, PhD Daniel
Dumitru, MD, PhD Brett L. Netherton, MS, CNIM
• ELECTROMYOGRAPHY (EMG) INTRO To THE MUSCLEACTIVITY
ASSESSMENT TECHNIQUE Kinesiology & Physical Education
CAGLIARI Sept 2015 Julie N. Côté, PhD
• Electromyography Fundamentals Gregory S. Rash, EdD

43. THANK YOU