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# Introduction

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 By about three years of age, gait is relatively mature (26) and the visually apparent unsteadiness has been replaced by a more stable walking pattern.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.

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).

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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