Various models have been used to describe distance running technique. Among these, the mass-spring model is fairly simple to use and apply, but when employed as a model, does not predict vertical force accurately especially when a heel strike is exhibited. The purpose of this article is to demonstrate how the mass-spring model can be modified to provide a simple, yet accurate prediction of ground reaction forces in distance running. Sixteen subjects ran on a force instrumented treadmill. Vertical forces during running at a self-selected pace were collected at 500 Hz. Vertical stiffness was calculated using the conventional mass-spring model with a constant stiffness and then a high-low method where stiffness was varied from a high to low value during the heel strike. Fishers z-test was used to compare correlations between predicted and measured ground reaction forces for each method of calculating stiffness. The high-low method of calculating stiffness provided a better fit of predicted to measured ground reaction forces than the constant stiffness method (p < 0.01). The high-low method of calculating stiffness avoids the difficulties of applying multiple masses, springs, or dampers while simply, yet accurately matching predicted to measured ground reaction forces.
Reprinted from the Journal of Sports Science and Medicine, 2, Iain Hunter, "A New Approach to Modeling Vertical Stiffness in Heel-Toe Distance Runners", 139-143, Copyright 2003, with permission from the Journal of Sports Science and Medicine.;