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### Subjects

Fifty boys and girls participated in this study. Parents of children ages 3 to 14 years old were asked if they would be willing to have their child participate in this study. If the child and parent were willing to participate, parents were asked to provide informed written consent and to fill out a questionnaire describing the child's medical history. Most children were attending a local day camp or a day-care center. Children were excluded if they had any disorders likely to affect gait, if they were unable to walk independently for eight minutes, or if they were born pre-maturely. Children were classified into three age groups: 3 and 4 year olds (n=11), 6 and 7 year olds (n=20), and 11 to 14 year olds (n=12). Five year old (n=3), eight year old (n=1) and ten year old (n=3) children were also studied. Height and body mass of the youngest, middle and oldest age groups were 105 2, 125 1, and 155 10 cm and 17.3 0.7, 25.3 0.9, 44.4 2.7 kg, respectively. Fifty percent of all subjects were boys and there were similar numbers of boys and girls in each age group. For comparison, we used data from historical controls, specifically, 10 healthy, young adults (ages 18-29) who walked for one hour around a large track under similar conditions as in the present study (12). All of the analysis methods performed on the children's data were applied to the first eight minutes of the longer data segments in this adult control group.