Foot clearance when crossing obstacles of different heights with the lead and trail limbs

In order to predict and prevent falls and fall-related injuries, it is crucial to understand the motor control for crossing obstacles. In real life, since obstacles do not always take regular shapes like rectangles, the lead and trail limbs sometimes need to negotiate different obstacle heights. The interlimb interaction in this process has remained unknown, since obstacle crossing studies commonly use a single-obstacle paradigm in which the obstacle height is the same for the lead and trail limbs.

We used a dual-obstacle paradigm to test whether the foot clearance over one obstacle was influenced by the contralateral obstacle's height.

Sixteen healthy young male and female participants (age: 22.5 ± 1.9 years) crossed over two obstacles placed side by side. Four obstacle conditions were made by combining obstacles of two heights (low, L, 9.0 cm; high, H, 22.5 cm) of the obstacles.In the LL condition, both obstacles were low, and in the LH condition, there was a low obstacle for the lead limb and a high one for the trail limb. Similarly, we also arranged HL and HH conditions. Each subject performed 20 trials per condition. We compared the vertical foot clearance, prestep distance, and poststep distance between the conditions.

The foot trajectory to step over the obstacles were affected by the contralateral obstacle's height. The vertical foot clearance of the trail limb was greater in the HL condition than in the LL condition. The vertical foot clearance of the lead limb was greater in the LH condition than in the LL condition.

The results suggest that the foot trajectory was not determined exclusively by the obstacle to be crossed. Instead, comprehensive information, including the height of the obstacle for the other limb, might be used for motor control during obstacle crossing.