TY - JOUR

T1 - Calculating sample entropy from isometric torque signals

T2 - methodological considerations and recommendations

AU - Raffalt, Peter C.

AU - Yentes, Jennifer M.

AU - Freitas, Sandro R.

AU - Vaz, João R.

N1 - Copyright © 2023 Raffalt, Yentes, Freitas and Vaz.

PY - 2023

Y1 - 2023

N2 - We investigated the effect of different sampling frequencies, input parameters and observation times for sample entropy (SaEn) calculated on torque data recorded from a submaximal isometric contraction. Forty-six participants performed sustained isometric knee flexion at 20% of their maximal contraction level and torque data was sampled at 1,000 Hz for 180 s. Power spectral analysis was used to determine the appropriate sampling frequency. The time series were downsampled to 750, 500, 250, 100, 50, and 25 Hz to investigate the effect of different sampling frequency. Relative parameter consistency was investigated using combinations of vector lengths of two and three and tolerance limits of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, and 0.4, and data lengths between 500 and 18,000 data points. The effect of different observations times was evaluated using Bland-Altman plot for observations times between 5 and 90 s. SaEn increased at sampling frequencies below 100 Hz and was unaltered above 250 Hz. In agreement with the power spectral analysis, this advocates for a sampling frequency between 100 and 250 Hz. Relative consistency was observed across the tested parameters and at least 30 s of observation time was required for a valid calculation of SaEn from torque data.

AB - We investigated the effect of different sampling frequencies, input parameters and observation times for sample entropy (SaEn) calculated on torque data recorded from a submaximal isometric contraction. Forty-six participants performed sustained isometric knee flexion at 20% of their maximal contraction level and torque data was sampled at 1,000 Hz for 180 s. Power spectral analysis was used to determine the appropriate sampling frequency. The time series were downsampled to 750, 500, 250, 100, 50, and 25 Hz to investigate the effect of different sampling frequency. Relative parameter consistency was investigated using combinations of vector lengths of two and three and tolerance limits of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, and 0.4, and data lengths between 500 and 18,000 data points. The effect of different observations times was evaluated using Bland-Altman plot for observations times between 5 and 90 s. SaEn increased at sampling frequencies below 100 Hz and was unaltered above 250 Hz. In agreement with the power spectral analysis, this advocates for a sampling frequency between 100 and 250 Hz. Relative consistency was observed across the tested parameters and at least 30 s of observation time was required for a valid calculation of SaEn from torque data.

KW - motor control

KW - muscle contraction

KW - nonlinear analysis

KW - regularity

KW - time series

UR - http://www.scopus.com/inward/record.url?scp=85162012210&partnerID=8YFLogxK

U2 - 10.3389/fphys.2023.1173702

DO - 10.3389/fphys.2023.1173702

M3 - Article

C2 - 37324377

AN - SCOPUS:85162012210

SN - 1664-042X

VL - 14

SP - 1173702

JO - Frontiers in Physiology

JF - Frontiers in Physiology

M1 - 1173702

ER -