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<H1><A NAME="SECTION00020000000000000000">Introduction</A></H1>





  
  

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<P>





  
  

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When young children first begin to walk, immature control of posture





  
  

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and gait results in large





  
  

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stride-to-stride fluctuations and frequent falls (5,23). By 





  
  

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about three years of age, gait is relatively mature  (26) and the





  
  

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visually apparent unsteadiness has been replaced by a more stable walking





  
  

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pattern.  Nonetheless,





  
  

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subtle changes in the development of neuromuscular control and





  
  

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locomotor function continue well beyond age





  
  

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three  (2,19,23,25,26).  





  
  

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Some studies suggest a decrease in walking variability 





  
  

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after this age  (21,24). However, a key unanswered question is





  
  

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whether  subtle changes in gait





  
  

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unsteadiness and stride-to-stride dynamics also occur beyond this age.





  
  

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<P>





  
  

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Even in healthy, young adults, the gait cycle duration -- the stride





  
  

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time -- fluctuates from one stride to the next in an apparently





  
  

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random, noisy manner  (11,16).  However, in young adults with





  
  

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intact neural control, the magnitude of these fluctuations is





  
  

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relatively small. Although the stride-to-stride changes





  
  

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appear to fluctuate randomly with no correlation between present and





  
  

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future stride times, the healthy adult locomotor system actually





  
  

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possesses ``memory'' such that the change from one stride to the next





  
  

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displays a subtle, ``hidden'' temporal structure that has been





  
  

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associated with long-range, fractal organization  (11,12).  In





  
  

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contrast, in persons with neurological disease and in older persons,





  
  

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especially those with a history of falls, stride-to-stride





  
  

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variability increases and the temporal organization of stride time





  
  

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dynamics is altered as well  (3,4,7,8,10,14).





  
  

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<P>





  
  

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These studies suggest that analysis of the stride time dynamics may





  
  

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also provide a window into the development of neuromuscular





  
  

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control in children.  Given the apparent parallels between the immature





  
  

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gait of children and the unsteady gait of older persons and





  
  

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persons with neurological impairment  (23),





  
  

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along with the subtle continued development of neural control beyond age three, we hypothesized





  
  

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that 





  
  

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stride time dynamics will not be fully  matured at this age. In the





  
  

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present study, we tested this hypothesis by measuring





  
  

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stride-to-stride fluctuations in the gait cycle duration of healthy





  
  

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children 3 to 14 years of age.  More specifically, we sought: i) to





  
  

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characterize the development of mature stride dynamics, ii) to





  
  

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determine at what ages changes in gait dynamics occur, and iii)





  
  

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to compare the gait dynamics of children to those of adults.





  
  

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