Human walking over visible and camouflaged curbs

Eleven volunteers walked with two different constant speeds (slow: 1.2 ± 0.1 m/s and fast: 1.7 ± 0.1 m/s) along an eight meter long walkway with two consecutive force plates in its center. The force plate of the first contact was fixed at ground-level concerning the first part of the walkway. The force plate at the second contact was adjustable in height as was the following part of the walkway. First, the subjects had to overcome three visible settings: for one the track was even (visible 0 cm), for the other two the force plate on the second contact and the following walkway both were lowered by either 10 cm (visible curb of 10 cm) or 20 cm (visible curb of 20 cm). Thereafter, for the camouflaged setting, the basic set-up was the same as for the visible 10 cm condition. Additionally, on the force plate of the second contact a wooden block with a height of 10 cm was randomly either present or absent. The wooden block was camouflaged with a thin, non-transparent sheet of paper, so that the subjects did not know if they were stepping down 10 cm (camouflaged curb of 10 cm) or walking one more step on the same level before stepping down (camouflaged 0 cm). For each condition kinetic and kinematic data were collected.