Based on their preliminary quantitative gait findings suggesting that limited passive hip extension range is a key functionally limiting impairment affecting gait, the investigators propose a supervised, specific stretching exercise with the aim to improve both peak hip extension and overall gait performance. While one goal is to demonstrate that reduced peak passive hip extension is a key, functionally significant, but reversible, impairment another is to improve our understanding of the relationship between impairment, functional limitation and gait ability.