Three-dimensional impact kinetics with foot-strike manipulations during running.

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,  ≤ 0.031) and foot-strike: ML (fore-foot and mid-foot strike > obvious heel strike,  ≤ 0.032), AP (fore-foot and mid-foot strikes > subtle-heel and obvious heel strikes,  ≤ 0.023). In each direction, the first loading rate peak occurred later during heel strike running relative to fore-foot ( ≤ 0.019), with vertical and 3D resultant impact durations exceeding shear (ML and AP,  ≤ 0.007) 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.