Ontogenetic changes in foot strike pattern and calcaneal loading during walking in young children.
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The assumption that the morphology of the human calcaneus reflects high and cyclical impact forces at heel strike during adult human walking has never been experimentally tested. Since a walking step with a heel strike is an emergent behavior in children, an ontogenetic study provides a natural experiment to begin testing the relationship between the mechanics of heel strike and calcaneal anatomy. This study examined the ground reaction forces (GRFs) of stepping in children to determine the location of the center of pressure (COP) relative to the calcaneus and the orientation and magnitude of ground reaction forces during foot contact. Three-dimensional kinematic and kinetic data were analyzed for 18 children ranging in age from 11.5 to 43.1 months. Early steppers used a flat foot contact (FFC) and experienced relatively high vertical and resultant GRFs with COP often anterior to the calcaneus. More experienced walkers used an initial heel contact (IHC) in which GRFs were significantly lower but the center of pressure remained under the heel a greater proportion of time. Thus, during FFC the foot experienced higher loading, but the heel itself was relatively wider and the load was distributed more evenly. In IHC walkers load was concentrated on the anterior calcaneus and a narrower heel, suggesting a need for increased calcaneal robusticity during development to mitigate injury. These results provide new insight into foot loading outside of typical mature contact patterns, inform structure-function relationships during development, and illuminate potential causes of heel injury in young walkers.