Figure 1.

Experimental set up and schematic explanation of some key concepts: (Figure 1.1.) Experimental set up. In front of the treadmill a bridge with an electromagnet is placed. The obstacle is attached to the magnet and will be released at different available response times. (Figure 1.2.) Available response time (ART): the time between obstacle presentation and the predicted (unaltered) landing time of the foot. (Figure 1.3.) Short Step Strategy (SSS): additional foot contact is made in front of the obstacle prior to the actual crossing manoeuvre. (Figure 1.4.) Long Step Strategy (LSS): the step during which the obstacle is presented is lengthened to cross the obstacle. Figure 1 is adapted from: Schillings AM, Van Wezel BMH, Duysens J. J Neurosci Meth 67:11-17 and Den Otter AR, Geurts AC, de Haart M, Mulder T, Duysens J. Exp Brain Res 161:180-92.