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<H1><A NAME="SECTION00020000000000000000">Introduction</A></H1>
<P>
When young children first begin to walk, immature control of posture
and gait results in large
stride-to-stride fluctuations and frequent falls (5,23). By
about three years of age, gait is relatively mature (26) and the
visually apparent unsteadiness has been replaced by a more stable walking
pattern. Nonetheless,
subtle changes in the development of neuromuscular control and
locomotor function continue well beyond age
three (2,19,23,25,26).
Some studies suggest a decrease in walking variability
after this age (21,24). However, a key unanswered question is
whether subtle changes in gait
unsteadiness and stride-to-stride dynamics also occur beyond this age.
<P>
Even in healthy, young adults, the gait cycle duration -- the stride
time -- fluctuates from one stride to the next in an apparently
random, noisy manner (11,16). However, in young adults with
intact neural control, the magnitude of these fluctuations is
relatively small. Although the stride-to-stride changes
appear to fluctuate randomly with no correlation between present and
future stride times, the healthy adult locomotor system actually
possesses ``memory'' such that the change from one stride to the next
displays a subtle, ``hidden'' temporal structure that has been
associated with long-range, fractal organization (11,12). In
contrast, in persons with neurological disease and in older persons,
especially those with a history of falls, stride-to-stride
variability increases and the temporal organization of stride time
dynamics is altered as well (3,4,7,8,10,14).
<P>
These studies suggest that analysis of the stride time dynamics may
also provide a window into the development of neuromuscular
control in children. Given the apparent parallels between the immature
gait of children and the unsteady gait of older persons and
persons with neurological impairment (23),
along with the subtle continued development of neural control beyond age three, we hypothesized
that
stride time dynamics will not be fully matured at this age. In the
present study, we tested this hypothesis by measuring
stride-to-stride fluctuations in the gait cycle duration of healthy
children 3 to 14 years of age. More specifically, we sought: i) to
characterize the development of mature stride dynamics, ii) to
determine at what ages changes in gait dynamics occur, and iii)
to compare the gait dynamics of children to those of adults.
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