Julius Wolff Institute for Biomechanics and Musculoskeletal Regeneration, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark.
Med Biol Eng Comput. 2019 Apr;57(4):759-764. doi: 10.1007/s11517-018-1920-2. Epub 2018 Nov 3.
Sample entropy (SaEn) has been used to assess the regularity of lower limb joint angles during walking. However, changing sampling frequency and the number of included strides can potentially affect the outcome. The present study investigated the effect of sample frequency and the number of included strides on the calculations of SaEn in joint angle signals recorded during treadmill walking. Eleven subjects walked at their preferred walking speed for 10 min, and SaEn was calculated on sagittal plane hip, knee, and ankle angle signals extracted from 50, 100, 200, 300, and 400 strides at sampling frequencies of 60, 120, 240, and 480 Hz. Increase in sampling frequency decreased the SaEn significantly for the three joints. The number of included strides had no effect on the SaEn calculated on the hip joint angle and only limited effect on the SaEn calculated on the knee and ankle joint signals. The present study suggests that the number of data points within each stride to a greater extent determines the size of the SaEn compared to the number of strides and emphasizes the use of a fixed number of data points within each stride when applying SaEn to lower limb joint angles during walking. Graphical abstract Sampling frequency influences sample entropy of kinematics during walking.
样本熵（SaEn）已被用于评估步行时下肢关节角度的规律性。然而，改变采样频率和包含的步数可能会影响结果。本研究探讨了采样频率和包含的步数对跑步机步行时关节角度信号记录的 SaEn 计算的影响。11 名受试者以其惯用的步行速度行走 10 分钟，从 50、100、200、300 和 400 步中提取矢状面髋关节、膝关节和踝关节角度信号，并在 60、120、240 和 480 Hz 的采样频率下计算 SaEn。采样频率的增加显著降低了三个关节的 SaEn。包含的步数对髋关节角度计算的 SaEn 没有影响，对膝关节和踝关节信号计算的 SaEn 只有有限的影响。本研究表明，与步数相比，每个步长内的数据点数在更大程度上决定了 SaEn 的大小，并强调在将 SaEn 应用于步行时下肢关节角度时，使用每个步长内固定数量的数据点。
