Fig. 1.

Uneven terrain treadmill. The uneven terrain surface is composed of manually shaped wooden slats affixed to a standard treadmill belt perpendicular to the direction of travel. The repeating pattern has four levels, in increments of 7, 7 and 8 mm from the lowest level (maximum depth of approximately 2.2 cm), selected as sufficiently shallow to enable a heel–toe gait to be maintained. The contours of the pattern were designed such that, unless deliberate targeting is attempted, each step on the surface should result in a slightly different interaction. The pattern is reflected and offset so that the left and right feet should have equal probability of encountering the same contours.