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On the Calculation of Sample Entropy Using Continuous and Discrete Human Gait Data

MORE Foundation, 18444 N 25th Ave., Suite 110, Phoenix, AZ 85023, USA
Center for Research in Human Movement Variability, Department of Biomechanics, University of Nebraska at Omaha, 6160 University Drive South, Omaha, NE 68182-0860, USA
Julius Wolff Institute for Biomechanics and Musculoskeletal Regeneration, Charité-Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany
Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen N 2200, Denmark
Author to whom correspondence should be addressed.
Entropy 2018, 20(10), 764;
Received: 1 August 2018 / Revised: 24 September 2018 / Accepted: 26 September 2018 / Published: 5 October 2018
(This article belongs to the Special Issue The 20th Anniversary of Entropy - Approximate and Sample Entropy)
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Sample entropy (SE) has relative consistency using biologically-derived, discrete data >500 data points. For certain populations, collecting this quantity is not feasible and continuous data has been used. The effect of using continuous versus discrete data on SE is unknown, nor are the relative effects of sampling rate and input parameters m (comparison vector length) and r (tolerance). Eleven subjects walked for 10-minutes and continuous joint angles (480 Hz) were calculated for each lower-extremity joint. Data were downsampled (240, 120, 60 Hz) and discrete range-of-motion was calculated. SE was quantified for angles and range-of-motion at all sampling rates and multiple combinations of parameters. A differential relationship between joints was observed between range-of-motion and joint angles. Range-of-motion SE showed no difference; whereas, joint angle SE significantly decreased from ankle to knee to hip. To confirm findings from biological data, continuous signals with manipulations to frequency, amplitude, and both were generated and underwent similar analysis to the biological data. In general, changes to m, r, and sampling rate had a greater effect on continuous compared to discrete data. Discrete data was robust to sampling rate and m. It is recommended that different data types not be compared and discrete data be used for SE. View Full-Text
Keywords: range of motion; joint angle; gait; complexity; regularity range of motion; joint angle; gait; complexity; regularity

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McCamley, J.D.; Denton, W.; Arnold, A.; Raffalt, P.C.; Yentes, J.M. On the Calculation of Sample Entropy Using Continuous and Discrete Human Gait Data. Entropy 2018, 20, 764.

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