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Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation
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Methodological variance associated with normalization of occupational upper trapezius EMG using sub-maximal reference

Jennie A Jackson1, Svend Erik Mathiassen, Patrick G Dempsey

  • 1Department of Kinesiology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1. ja2jacks@ahsmail.uwaterloo.ca

Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology
|December 25, 2007
PubMed
Summary

Normalization of trapezius electromyography (EMG) by reference voluntary exertions (RVE) introduces minimal variance (<4.4%). Increasing RVE repeats offers diminishing returns for improving EMG data precision in occupational studies.

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Area of Science:

  • Occupational Ergonomics
  • Biomedical Engineering
  • Muscle Physiology

Background:

  • Electromyography (EMG) is crucial for assessing muscle activity in occupational settings.
  • Normalization of EMG data using reference voluntary exertions (RVE) is a common practice.
  • Understanding variance introduced by normalization is key to accurate EMG interpretation.

Purpose of the Study:

  • To quantify the variance in trapezius EMG introduced by normalization using sub-maximal RVE.
  • To investigate how increasing normalization efforts impact the precision of occupational EMG estimates.
  • To compare the effect of normalization changes versus other data collection strategies on EMG precision.

Main Methods:

  • Women performed RVE contractions and 30 minutes of cyclic assembly work.
  • Work cycle EMG was normalized to each RVE trial.
  • Variance components (subject, day, cycle, normalization trial) were determined.
  • Simulations explored the impact of altering data collection parameters (subjects, days, cycles, RVEs) on exposure mean precision.

Main Results:

  • Normalization introduced a unique variance component, but it was small (<4.4% of total variance).
  • Simulations showed marginal improvements in group exposure mean precision beyond three RVE repeats for single-day data.
  • For multi-day data, precision gains were limited beyond two RVEs.

Conclusions:

  • The variance introduced by RVE normalization in trapezius EMG is minimal.
  • Resource allocation simulations suggest that increasing RVE repeats beyond 2-3 offers limited benefits for improving occupational EMG estimate precision.
  • Optimizing the number of subjects and days may be more impactful than increasing RVE repetitions for enhancing EMG data reliability.