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--- a +++ b/jap/node9.html @@ -0,0 +1,85 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 3.0//EN"> +<!--Converted with LaTeX2HTML 96.1-h (September 30, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --> +<HTML> +<HEAD> +<TITLE>Stride Time Variability Measures</TITLE> +<META NAME="description" CONTENT="Stride Time Variability Measures"> +<META NAME="keywords" CONTENT="gait-reprint"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<LINK REL=STYLESHEET HREF="gait-reprint.css"> +</HEAD> +<BODY LANG="EN" bgcolor="white"> + <A NAME="tex2html90" HREF="node10.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="/icons/latex2html/next_motif.png"></A> <A NAME="tex2html88" HREF="node8.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="/icons/latex2html/up_motif.png"></A> <A NAME="tex2html82" HREF="node8.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="/icons/latex2html/previous_motif.png"></A> <BR> +<B> Next:</B> <A NAME="tex2html91" HREF="node10.html">Temporal Structure Measures</A> +<B>Up:</B> <A NAME="tex2html89" HREF="node8.html">Results</A> +<B> Previous:</B> <A NAME="tex2html83" HREF="node8.html">Results</A> +<BR> <P> +<H3><A NAME="SECTION00040100000000000000">Stride Time Variability Measures</A></H3> +<P> +Representative examples of the effects of age on the stride time +fluctuations are shown in Figure 1. The stride-to-stride variability +is largest in the four year old, lower in the seven year old, +and smaller still in the eleven year old child. As summarized in Table 2, +there was a highly significant effect of age on variability +(p < .0001). Both the standard deviation and coefficient of +variation (CV) were significantly larger in the 3 and 4 year olds +compared to the 6 and 7 year olds (p < .0001). In addition, these +measures were significantly larger in the 6 and 7 year olds compared +to the 11 to 14 year old children (p < .005). Of note, the +stride-to-stride variability of the 11 to 14 year old children was +closest to the values obtained in healthy, young adults (CV += 1.3 <IMG WIDTH=12 HEIGHT=27 ALIGN=MIDDLE ALT="tex2html_wrap_inline288" SRC="img6.png"> 0.1 % in the young adults and 2.1 <IMG WIDTH=12 HEIGHT=27 ALIGN=MIDDLE ALT="tex2html_wrap_inline288" SRC="img6.png"> 0.1 % in +the 11 to 14 year olds). +<P> +In the representative examples shown in Figure 1, the local average of the stride time of the oldest child is relatively constant throughout the walk. In +contrast, for the two younger children, the local average appears to +change from time to time. Therefore, we next +addressed two questions: 1) Is the increased variability in the +younger children simply due to fatigue during this walk? 2) Is this +increased variability due to a change in rate during the walk (e.g., +long-term slowing down or speeding up), and not indicative of +short-term, stride-to-stride unsteadiness per se? +<P> +To evaluate these questions, we detrended each time series to minimize +the effects of any local changes in average stride. Figure 2 shows +the results for the times series shown in Figure 1. Even after +detrending, variability is largest for the four year old child and +smallest for the oldest child. This inverse relationship between +variability and age after detrending was found in general for all subjects as +well. The standard deviation of the detrended time series, a measure +of the dispersion or variability, was significantly larger in the 3 +and 4 year olds compared to the 6 and 7 year old (p < .0001) and in +the 6 and 7 year olds compared to the oldest children (p = .004). +<P> +As a further test of these findings, we analyzed +sub-sections of each subject's time series to find the 30 consecutive +strides with the lowest CV. (A data analysis window was moved forward 5 strides at a +time across the time series and in each window the CV was +calculated). Variability during this segment should be largely +independent of a subject's speeding up or slowing down during the +trial and reflects the ``best-effort'' of the neuromuscular control +system. For the data shown in Figures 1 and 2, the CV calculated in +this manner was 3.8, 1.9 and 1.1 % for the 4, 7 and 11 year old, +respectively. Figure 3 shows the results of this lowest variability +time segment for all subjects. Even during a relatively short time +period, the fluctuations from one stride to the next were significantly +increased in the 3 and 4 year olds compared to the 6 and 7 year olds +(p < .0001) and in the 6 and 7 year olds compared to the oldest +children (p < .0001). In fact, the CV of each of the oldest children +was lower than that of all of the 3 and 4 year old children. +<P> +Finally, to confirm that the increased variability in the younger +children was not simply due to fatigue or a change of speed during the +walk, we studied the variability of only the first 30 strides. As was the +case for the entire walk, both the standard deviation and coefficient +of variation were significantly larger in the 3 and 4 year olds +compared to the 6 and 7 year olds (p < .0001) and in the 6 and 7 +year olds compared to the oldest children (p < .0003) (Table 2). +<P> +<HR><A NAME="tex2html90" HREF="node10.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="/icons/latex2html/next_motif.png"></A> <A NAME="tex2html88" HREF="node8.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="/icons/latex2html/up_motif.png"></A> <A NAME="tex2html82" HREF="node8.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="/icons/latex2html/previous_motif.png"></A> <BR> +<B> Next:</B> <A NAME="tex2html91" HREF="node10.html">Temporal Structure Measures</A> +<B>Up:</B> <A NAME="tex2html89" HREF="node8.html">Results</A> +<B> Previous:</B> <A NAME="tex2html83" HREF="node8.html">Results</A> +</BODY> +</HTML>