Figure 8.

GROUND-CONTACT TIME can be derived from the model as a function of track stiffness. In this graph of the function, normalized, or dimensionless, values of each parameter have been used so that theoretical results (curve) can be compared with experimental findings for many runners (black dots). Ground-contact time bas been normalized by dividing the time on a compliant surface t_c by the time on a hard surface t₀; track stiffness bas been normalized by dividing the track stiffness k_t by the runner’s stiffness k_m. Because of the damping of human muscle ground-contact time does not decrease continuously as track stiffness increases but reaches minimum at stiffnesses between two and four times that of average athelete (color).