Fig. 1. The running track setup near the force plates. (A) View from above. The track is instrumented with two force plate sections. The first one (first contact) consists of two small Kistler force plates (Kistler 9282BA, size 600 mmx400 mm) and the second (second contact) of one large Kistler force plate (Kistler 9285C, size 900 mmx600 mm). (B) View from the side. Before, between and after the force plates the track is uneven (vertical perturbation between 1 and 2.5 cm). These small perturbations are made with wooden bars (width 120 mm). Note that in this sketch the ratio between the width of the bars and the length of the force plates is exaggerated for clarity. The first force plate represents ground level of vertical height zero. The second force plate acts as a single perturbation (step), which is variable in vertical height. Four track conditions were measured: level track (no perturbation at all) and an uneven track, i.e. varying height of bars before and after the force plates plus vertical steps of 5, 10 and 15 cm onto the second force plate.