Three-dimensional impact kinetics with foot-strike manipulations during running.
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BACKGROUND: Lack of an observable vertical impact peak in fore/mid-foot running has been suggested as a means of reducing lower extremity impact forces, although it is unclear if impact characteristics exist in other axes. The purpose of the investigation was to compare three-dimensional (3D) impact kinetics among foot-strike conditions in over-ground running using instantaneous loading rate-time profiles. METHODS: Impact characteristics were assessed by identifying peak loading rates in each direction (medial-lateral (ML), anterior-posterior (AP), vertical, and 3D resultant) following foot-strike instructions (fore-foot, mid-foot, subtle heel, and obvious heel strike). Kinematic and kinetic data were analyzed among 9 male participants in each foot-strike condition. RESULTS: Loading rate peaks were observed in each direction and foot-strike condition, differing in magnitude by direction (3D resultant and vertical>AP>ML, p0.031) and foot-strike: ML (fore-foot and mid-foot strike>obvious heel strike, p0.032), AP (fore-foot and mid-foot strikes>subtle-heel and obvious heel strikes, p0.023). In each direction, the first loading rate peak occurred later during heel strike running relative to fore-foot (p0.019), with vertical and 3D resultant impact durations exceeding shear (ML and AP, p0.007) in each condition. CONCLUSION: Loading rate-time assessment identified contrasting impact characteristics in each direction and the 3D resultant following foot-strike manipulations, with potential implications for lower extremity structures in running.
