Form factor analysis of the surface electromyographic interference pattern
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Updated: Dec 21, 2025
Extraction of the EPP Component from the Surface EMG
Published on: December 16, 2009
Sanjeev D Nandedkar1,2, Paul E Barkhaus2, Erik V Stålberg3
1Natus Neuro, Hopewell Junction, New York.
Introduction:
In contrast to needle electromyography (EMG), surface EMG recordings are painless. It is of interest to develop methods to analyze surface EMG for diagnostic purposes.
Methods:
Surface EMG interference pattern (SIP) recordings from the abductor pollicis brevis muscle of healthy subjects and subjects with amyotrophic lateral sclerosis (ALS) were analyzed by measuring root-mean-square (RMS) voltage, mean rectified voltage, form factor (FF), and the clustering index (CI). The FF vs SIP area plot was used for analysis.
Results:
The SIP FF was increased and abnormal in ALS subjects, especially when SIP area was less than 200 mVms. Power regression showed a faster FF decline with SIP area in ALS patients than in healthy subjects. The CI and FF showed a strong correlation.
Discussion:
FF is easy to calculate and demonstrates abnormalities in ALS patients.
