Fig. 2.

Walkway (a) and gait protocol (b) for the test of the dynamic stability. The walkway (a) included one covered, exchangeable element, which allowed changing the surface condition from hard to soft without the knowledge of the participants. Three valid gait trials on the hard surface formed the baseline and were followed by one unexpected soft surface trial (b). This soft trial was performed to induce reactive behavior. Analysis was made for the step prior to the perturbation and the step after the perturbation (c)