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Related Experiment Video

Updated: Dec 8, 2025

Dissection of Single Skeletal Muscle Fibers for Immunofluorescent and Morphometric Analyses of Whole-Mount Neuromuscular Junctions
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Updated size index valid for both neurogenic and myogenic changes.

Masahiro Sonoo1, Go Ogawa1, Keiichi Hokkoku1

  • 1Department of Neurology, Teikyo University School of Medicine, Tokyo, Japan.

Muscle & Nerve
|September 17, 2020
PubMed
Summary

The size index (SI) effectively distinguishes neurogenic motor unit potentials (MUPs) and shows promise for myogenic MUPs in electromyography. A revised SI (rSI) offers comparable sensitivity for neurogenic MUPs.

Keywords:
motor unit potential parametersmyogenic disordersquantitative EMGrevised size indexsize index

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Area of Science:

  • Neurology
  • Electromyography
  • Motor Unit Potential Analysis

Background:

  • The size index (SI) is a motor unit potential (MUP) parameter used in concentric needle electromyography.
  • SI is calculated from amplitude and area/amplitude, effectively discriminating between control and neurogenic MUPs.

Purpose of the Study:

  • To investigate the application of SI to myogenic MUPs using expanded datasets.
  • To evaluate a revised SI (rSI) incorporating a logarithmic scale for area/amplitude.

Main Methods:

  • MUPs were collected from biceps brachii (BB) and tibialis anterior (TA) muscles.
  • A revised SI (rSI) was defined using a logarithmic scale for area/amplitude, with optimized coefficients.
  • Muscles with clear neurogenic or myogenic changes were selected for analysis.

Main Results:

  • For neurogenic MUPs, SI and rSI demonstrated high sensitivity (e.g., 82.1% for SI in BB) exceeding conventional parameters like area.
  • For myogenic MUPs, the revised SI (rSIm) showed sensitivity (e.g., 24.5% in TA) comparable to duration.

Conclusions:

  • The size index (SI), including its revised form (rSI), shows potential as a novel parameter for MUP analysis.
  • SI demonstrates effectiveness in differentiating neurogenic MUPs and emerging utility for myogenic MUPs.