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Calculating sample entropy from isometric torque signals: methodological considerations and recommendations.

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Summary
This summary is machine-generated.

Optimal sample entropy (SaEn) calculation from isometric contraction torque data requires specific parameters. A sampling frequency between 100-250 Hz and at least 30 seconds of observation time ensure valid SaEn results.

Keywords:
motor controlmuscle contractionnonlinear analysisregularitytime series

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Area of Science:

  • Biomechanics
  • Physiology
  • Signal Processing

Background:

  • Sample entropy (SaEn) quantifies time-series regularity.
  • Accurate SaEn calculation is crucial for analyzing physiological signals like muscle torque.
  • Determining optimal parameters for SaEn in isometric contractions is essential for reliable data interpretation.

Purpose of the Study:

  • To investigate the impact of sampling frequency, input parameters, and observation duration on SaEn values derived from isometric knee flexion torque data.
  • To establish optimal parameters for robust SaEn analysis in submaximal isometric contractions.

Main Methods:

  • Torque data from 46 participants performing isometric knee flexion at 20% maximal voluntary contraction were collected at 1000 Hz.
  • Power spectral analysis guided downsampling to evaluate frequencies from 25 to 750 Hz.
  • SaEn was calculated using varying vector lengths (2-3), tolerance limits (0.1-0.4), data lengths (500-18000 points), and observation times (5-90 s).

Main Results:

  • SaEn values increased below 100 Hz and remained stable above 250 Hz, supporting a sampling frequency of 100-250 Hz.
  • Consistent SaEn results were found across tested parameter combinations (vector length, tolerance, data length).
  • A minimum observation time of 30 seconds was necessary for valid SaEn calculations.

Conclusions:

  • A sampling frequency between 100 Hz and 250 Hz is recommended for SaEn analysis of isometric torque data.
  • Parameter selection for SaEn calculation showed relative consistency, but observation time is critical.
  • At least 30 seconds of data are required for reliable SaEn quantification in this context.