D24 Contact with the Ground

Topic

This assessment of ground contact analyzes the specific way the athlete's foot interacts with the supporting surface: the temporal pattern of the ground reaction force, the type of foot contact (heel, midfoot, or forefoot), the point of force application, the loading rate, and the final impulse generated against the surface.

A high-sampling-rate force platform—the same one used in another model in this set—precisely captures both the initial passive impact peak of the vertical ground reaction force (which occurs primarily during heel strikes) and the subsequent active impact peak of that same vertical force.

Conversely, an instrumented insole with a pressure sensor maps the distribution of plantar pressure across different zones of the athlete's foot—heel, arch, metatarsus, or toes—throughout the entire duration of ground contact.

A reactive strength index combines the athlete's jump height (the same height measured in another model in this set) and ground contact time (the same time measured in a different model in this set) during a repeated-rebound exercise. A shorter ground contact time for a given jump height results in a higher reactive strength index. Consequently, this model—based on the interaction between the athlete's foot and the ground—reveals that a bilateral asymmetry between the final impulse derived from the ground reaction force of one leg and that of the other indicates an imbalance in the load borne by each limb; this is the same bilateral asymmetry that characterizes the biomechanical imbalance between the legs in another model within this framework. Based on the ground reaction force (measured across its three components), plantar pressure distribution, and contact time, this diagnostic determines the final contact impulse, loading rate, point of application, passive and active impact peaks, reactive strength index, and the bilateral asymmetry that concludes the model. If this final bilateral asymmetry between the athlete's legs is greater, the resulting imbalance in the load borne by each limb becomes even more pronounced.

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