TY - JOUR
T1 - Fractal analysis of gait in people with Parkinson's disease
T2 - three minutes is not enough
AU - Marmelat, Vivien
AU - Meidinger, Ryan L.
N1 - Funding Information:
This work was supported by the University Committee on Research and Creative Activity of the University of Nebraska at Omaha , and by the Center for Research in Human Movement Variability of the University of Nebraska at Omaha, NIH ( P20GM109090 ). The study sponsors were not involved in the collection, analysis and interpretation of data, in the writing of the manuscript, nor in the decision to submit the manuscript for publication. The views expressed are those of the authors and not necessarily those of the NIH. The authors thank Daniel Jaravata for his support with data processing.
Publisher Copyright:
© 2019 Elsevier B.V.
PY - 2019/5
Y1 - 2019/5
N2 - Background: The fractal dynamics of gait variability in people with Parkinson's disease has been studied by applying the detrended fluctuation analysis (DFA) to short time series (<200 strides). However, DFA is sensitive to time series length, and it is unclear if DFA results from short time series are reliable and if they reflect the fractal dynamics of longer time series. Research question: Is DFA reliable when applied to short time series? Methods: We applied DFA to stride time series from five 3-min trials and one 15-min trial in 12 people with Parkinson's disease, 14 healthy older adults and 14 healthy young adults walking overground. Within each group, intraclass correlations (ICC 3,1) were performed to assess the reliability of i) the five 3-min trials together, ii) each 3-min trials to the 15-min trial, and iii) the first 150 strides from the 15-min trial to the full 15-min trial. Results: Our three main findings are that 1) stride time α-DFA values are not consistent from trial-to-trial for short stride time series, 2) stride time α-DFA values from each 3-min trials are not consistent when compared to stride time α-DFA values from a 15-min trial, and 3) stride time α-DFA values from the first 150 strides of the 15-min trial are not consistent when compared to α-DFA values from the full 15-min trial. Significance: Our results confirm that α-DFA values from 3-min walking trials are not reliable, and that they do not reflect the scale invariant properties of longer time series. This suggests that previous studies assessing the fractal dynamics of gait variability from about 3-min walking must be interpreted with caution. A major clinical implication is that DFA cannot be used to study gait in people unable to perform 500 strides continuously.
AB - Background: The fractal dynamics of gait variability in people with Parkinson's disease has been studied by applying the detrended fluctuation analysis (DFA) to short time series (<200 strides). However, DFA is sensitive to time series length, and it is unclear if DFA results from short time series are reliable and if they reflect the fractal dynamics of longer time series. Research question: Is DFA reliable when applied to short time series? Methods: We applied DFA to stride time series from five 3-min trials and one 15-min trial in 12 people with Parkinson's disease, 14 healthy older adults and 14 healthy young adults walking overground. Within each group, intraclass correlations (ICC 3,1) were performed to assess the reliability of i) the five 3-min trials together, ii) each 3-min trials to the 15-min trial, and iii) the first 150 strides from the 15-min trial to the full 15-min trial. Results: Our three main findings are that 1) stride time α-DFA values are not consistent from trial-to-trial for short stride time series, 2) stride time α-DFA values from each 3-min trials are not consistent when compared to stride time α-DFA values from a 15-min trial, and 3) stride time α-DFA values from the first 150 strides of the 15-min trial are not consistent when compared to α-DFA values from the full 15-min trial. Significance: Our results confirm that α-DFA values from 3-min walking trials are not reliable, and that they do not reflect the scale invariant properties of longer time series. This suggests that previous studies assessing the fractal dynamics of gait variability from about 3-min walking must be interpreted with caution. A major clinical implication is that DFA cannot be used to study gait in people unable to perform 500 strides continuously.
KW - Detrended fluctuation analysis
KW - Fractal fluctuations
KW - Gait variability
KW - Overground walking
KW - Parkinson's disease
KW - Stride time series
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U2 - 10.1016/j.gaitpost.2019.02.023
DO - 10.1016/j.gaitpost.2019.02.023
M3 - Article
C2 - 30909002
AN - SCOPUS:85063231122
VL - 70
SP - 229
EP - 234
JO - Gait and Posture
JF - Gait and Posture
SN - 0966-6362
ER -