a b/jap/node9.html 

  1
  
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 3.0//EN">





  
  

  2
  
<!--Converted with LaTeX2HTML 96.1-h (September 30, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds -->





  
  

  3
  
<HTML>





  
  

  4
  
<HEAD>





  
  

  5
  
<TITLE>Stride Time Variability Measures</TITLE>





  
  

  6
  
<META NAME="description" CONTENT="Stride Time Variability Measures">





  
  

  7
  
<META NAME="keywords" CONTENT="gait-reprint">





  
  

  8
  
<META NAME="resource-type" CONTENT="document">





  
  

  9
  
<META NAME="distribution" CONTENT="global">





  
  

  10
  
<LINK REL=STYLESHEET HREF="gait-reprint.css">





  
  

  11
  
</HEAD>





  
  

  12
  
<BODY LANG="EN" bgcolor="white">





  
  

  13
  
 <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>





  
  

  14
  
<B> Next:</B> <A NAME="tex2html91" HREF="node10.html">Temporal Structure Measures</A>





  
  

  15
  
<B>Up:</B> <A NAME="tex2html89" HREF="node8.html">Results</A>





  
  

  16
  
<B> Previous:</B> <A NAME="tex2html83" HREF="node8.html">Results</A>





  
  

  17
  
<BR> <P>





  
  

  18
  
<H3><A NAME="SECTION00040100000000000000">Stride Time Variability Measures</A></H3>





  
  

  19
  
<P>





  
  

  20
  
Representative examples of the effects of age on the stride time





  
  

  21
  
fluctuations are shown in Figure 1.  The stride-to-stride variability





  
  

  22
  
is largest in the four year old, lower in the seven year old, 





  
  

  23
  
and smaller still in the eleven year old child. As summarized in Table 2,





  
  

  24
  
there was a highly significant effect of age on variability 





  
  

  25
  
(p &lt; .0001).  Both the standard deviation and coefficient of





  
  

  26
  
variation (CV) were significantly larger in the 3 and 4 year olds





  
  

  27
  
compared to the 6 and 7 year olds (p &lt; .0001). In addition, these





  
  

  28
  
measures were significantly larger in the 6 and 7 year olds compared





  
  

  29
  
to the 11 to 14 year old children (p &lt; .005).  Of note, the





  
  

  30
  
stride-to-stride variability of the 11 to 14 year old children was





  
  

  31
  
closest to the values obtained  in healthy, young adults (CV





  
  

  32
  
= 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





  
  

  33
  
the 11 to 14 year olds).





  
  

  34
  
<P>





  
  

  35
  
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





  
  

  36
  
contrast, for the two younger children, the local average appears to





  
  

  37
  
change from time to time.   Therefore, we next





  
  

  38
  
addressed two questions: 1) Is the increased variability in the





  
  

  39
  
younger children simply due to fatigue during this walk? 2) Is this





  
  

  40
  
increased variability due to a change in rate during the walk (e.g.,





  
  

  41
  
long-term slowing down or speeding up), and not indicative of





  
  

  42
  
short-term, stride-to-stride unsteadiness per se?





  
  

  43
  
<P>





  
  

  44
  
To evaluate these questions, we detrended each time series to minimize





  
  

  45
  
the effects of any local changes in average stride.  Figure 2 shows





  
  

  46
  
the results for the times series shown in Figure 1.  Even after





  
  

  47
  
detrending, variability is largest for the four year old child and





  
  

  48
  
smallest for the oldest child.  This inverse relationship between





  
  

  49
  
variability and age after detrending was found in general for all subjects as





  
  

  50
  
well.  The standard deviation of the detrended time series, a measure





  
  

  51
  
of the dispersion or variability, was significantly larger in the 3





  
  

  52
  
and 4 year olds compared to the 6 and 7 year old (p &lt; .0001) and in





  
  

  53
  
the 6 and 7 year olds compared to the oldest children (p = .004).





  
  

  54
  
<P>





  
  

  55
  
As a further test of these findings, we analyzed





  
  

  56
  
sub-sections of each subject's time series to find the 30 consecutive





  
  

  57
  
strides with the lowest CV. (A data analysis window was moved forward 5 strides at a





  
  

  58
  
time across the time series and in each window the CV was





  
  

  59
  
calculated). Variability during this segment should be largely





  
  

  60
  
independent of a subject's speeding up or slowing down during the





  
  

  61
  
trial and reflects the ``best-effort'' of the neuromuscular control





  
  

  62
  
system.  For the data shown in Figures 1 and 2, the CV calculated in





  
  

  63
  
this manner was 3.8, 1.9 and 1.1 % for the 4, 7 and 11 year old,





  
  

  64
  
respectively.  Figure 3 shows the results of this lowest variability





  
  

  65
  
time segment for all subjects.  Even during a relatively short time





  
  

  66
  
period, the fluctuations from one stride to the next were significantly





  
  

  67
  
increased in the 3 and 4 year olds compared to the 6 and 7 year olds





  
  

  68
  
(p &lt; .0001) and in the 6 and 7 year olds compared to the oldest





  
  

  69
  
children (p &lt; .0001). In fact, the CV of each of the oldest children





  
  

  70
  
was lower than that of all of the 3 and 4 year old children.





  
  

  71
  
<P>





  
  

  72
  
Finally, to confirm that the increased variability in the younger





  
  

  73
  
children was not simply due to fatigue or a change of speed during the





  
  

  74
  
walk, we studied the variability of only the first 30 strides. As was the





  
  

  75
  
case for the entire walk, both the standard deviation and coefficient





  
  

  76
  
of variation were significantly larger in the 3 and 4 year olds





  
  

  77
  
compared to the 6 and 7 year olds (p &lt; .0001) and in the 6 and 7





  
  

  78
  
year olds compared to the oldest children (p &lt; .0003) (Table 2).





  
  

  79
  
<P>





  
  

  80
  
<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>





  
  

  81
  
<B> Next:</B> <A NAME="tex2html91" HREF="node10.html">Temporal Structure Measures</A>





  
  

  82
  
<B>Up:</B> <A NAME="tex2html89" HREF="node8.html">Results</A>





  
  

  83
  
<B> Previous:</B> <A NAME="tex2html83" HREF="node8.html">Results</A>





  
  

  84
  
</BODY>





  
  

  85
  
</HTML>