The ability to safely and efficiently negotiate stairs is an essential skill for independent ambulation. To date, basic research to identify biomechanical and physical costs is limited in older adults. In persons with stroke, this aspect of mobility is virtually unexplored. The main objective of this thesis was to investigate biomechanical alterations during stair negotiation and to evaluate the physical costs of the task in older adults and persons with stroke. This was approached by conducting four studies. The first study identified age-related alterations in joint kinetics during stair negotiation. The results showed age-related differences in moment magnitudes, an exaggerated net support moment and sustained abductor moments through stance. To gain insight into these adaptive changes with respect to mechanical efficiency, the second study evaluated age-related changes in mechanical energy transfers during stair negotiation. During ascent, older adults achieve similar efficiencies as young adults by slowing their cadence. During descent, age-related differences in mechanical energy expenditures and related variances in mechanical energy compensation coefficients reflect a loss in mechanical efficiency. The impact was likely the provision of enhanced extensor support and stability. The results also highlight a functional role for concentric energy expenditures during descent. The third study provided a detailed biomechanical description of stair negotiation in people with stroke, revealing important differences in how stroke survivors manage stairs and how handrail use modifies the magnitudes of lower limb joint moments. The fourth study evaluated the strength and aerobic requirement of stair ambulation in persons with stroke. The findings reveal increased costs of the task, primarily due to reduced neuromuscular and aerobic capacities and serve to identify factors that may be limiting during stair negotiation.

This thesis provides new information regarding movement control in older adults during stair negotiation, providing a normative benchmark of age-related alterations in movement patterns. In persons with stroke, this work is the first to quantify the biomechanical patterns and physical requirements of stair negotiation. Future work may extend these findings to explore mobility challenges in persons with greater levels of impairment as well as guide the development of targeted and task oriented rehabilitation programs.