Figure 1.

Illustration of level walking strides (grey feet) and non-level strides (black feet) for (a) level surface to an uphill surface (L-UP), (b) uphill surface only (UP), (c) level surface to a downhill surface (L-DN) and (d) downhill surface (DN) only. Shaded regions represent the hill surface and non-shaded regions represent the level surface. The foot placement locations represent actual changes in step length as well as step width at the heel and toe. Each small box is equal to a 3 × 3 cm square (modified from Gottschall et al. [30]).