Effects of conflicting constraints and age on strategy choice in stepping down during gait.

For negotiating a step down during gait, as in stepping from a curb, two different strategies can be used, i.e. heel landing and toe landing. Toe landing allows more negative work by the leading leg to reduce the momentum gained during the descent, which facilitates maintaining stability but reduces walking velocity. We therefore hypothesized that subjects would use a toe landing less frequently when instructed to walk faster and when negotiating smaller height differences. Furthermore, expecting that older adults would prioritize stability over maintaining gait velocity, we hypothesized that they would use toe landing more frequently than young adults. Two groups (young: 23+/-1 years, n=8; old: 73+/-5 years, n=17) walked over a 10-m walkway at 3-5 km/h to step down a single step of 5-15 cm halfway. In both groups, toe landing was used less frequently for lower steps and less frequently at higher velocities. Older participants used toe landing more frequently and more consistently than young participants. This preference for toe landing is suggested to reflect adaptive behavior to enhance gait stability, rather than an inability to use a heel landing.