ELECTROMYOGRAM

Amit Sethi

Pre-doc Rehab Sciences,

MS OTR/L

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.

INTRODUCTION Contd.

EMG Apparatus Muscle Structure/EMG

ELECTRICAL CHARACTERITICS

• 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.

• Damage to motor units can be expected at ranges between 450 and 780 mV

ELECTRODE TYPES

Intramuscular -

Needle Electrodes

Extramuscular - Surface Electrodes

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.

EMG Contd.EMG Contd.

• Muscle Signals are Analog in nature.

• EMG signals are also collected over a specific period of time.

Analog Signal

EMG Contd.EMG Contd.EMG processing:

Amplification & Filtering

Signal pick up

Conversion of Analog signals to Digital signals

Computer

APPLICATION OF EMG

• EMG can be used for diagnosis of Neurogenic or Myogenic Diseases.

• You tube link of EMG

SAMPLE EMG DATA

BIOMECHANICSBIOMECHANICS

• Biomechanics is the research and analysis of the mechanics of living organisms.

• KINEMATICS – The branch of Biomechanics concerned with describing the motion of bodies.

• KINETICS- The branch of biomechanics concerned with explaining the causes of body motions.

KINEMATICS Contd.KINEMATICS Contd.Data is usually collected

with Motion Capture Devices over a specific time period.

VICON Motion Analysis

Corporation Qualysis

Typical Set up of Motion Analysis Lab

SAMPLE KINEMATIC DATA

SAMPLE KINEMATIC DATA

SAMPLE KINEMATIC DATA

KINEMATICS DATA ANALYSIS• Aim: to identify the variability in reaching movement in

normal and stroke individuals. • Outcome Variable: Elbow Joint Angle.• Magnitude of variability was analyzed with Std.

Deviation.• Structure of variability in elbow angles was computed

via IE using MATLAB. H = Log2 (1/Pi) Pi = probability that a given event will occur. Pi α1/H. • Higher values of IE suggest - more uncertainty.• Lower values of IE suggest- less uncertainty

(increased stability). of

RESULTS

Subject SD Pre SD Post IE Pre IE Post1 4.54 1.80 0.58

0.80

2 3.69 2.67 0.79 0.50

Control SD = 2.68 IE = 2.33

CONCLUSION

• Variability/Uncertainity in movement is higher in normals as compared to individuals with Stroke.

• This variability could be correlated with adaptability in movement which is decreased upon nervous system damage in Stroke.

• Large data is required to generalize these results.