The Effects of Varying Speed on the Biomechanics of Stair Ascending and Descending in Healthy Young Adults: Inverse Kinematics, Inverse Dynamics, Electromyography and a Pilot Study for Computational Muscle Control and Forward Dynamics

Stairs are a frequently encountered obstacle in daily life. The ability to negotiate stairs without difficulty or pain is important to quality of life. Although it is a simple task for healthy persons, ascending and descending stairs can be very challenging when motor functions are diminished (e.g., in elderly persons, persons with physical disabilities and in persons who have experienced trauma to their lower extremities). Conditions such as stroke, cerebral palsy (CP), osteoarthritis (OA) both before and after total knee replacement (TKR), and anterior cruciate ligament (ACL) injuries impair the ability to negotiate stairs. Because many individuals with neuromuscular impairments walk and ascend/descend stairs slowly, it is important to isolate functional task from other factors such as age, muscle weakness, etc. Previous studies have developed the normative data for kinematics, kinetics and muscles or groups of muscles that contribute to specific subtasks of walking at various speeds. However, the normative data for various speeds of stair climbing, as prevalent a task and as periodic as level over the ground walking, has yet to be established. The purpose of this thesis is to create a normative database characterizing the effect of speed on the biomechanics in healthy young adults while ascending and descending stairs. Kinematic, kinetic and EMG data was collected for 12 healthy subjects while ascending/descending stairs at three speeds (slow, self selected, and quick). Computational modeling was employed in ViconNexus and OpenSim to determine joint ii angles, joint flexion moments, ground reaction forces and muscle activations during stair ascending/descending at the three speeds. Peak ground reaction forces, peak flexion angles, peak flexion and extension moments and angles at foot strike, midtstance and foot off were compared during stair climbing for the three speeds using a one-way ANOVA (p less than 0.05) with repeated measures. Post hoc analysis was performed with paired t-tests and a bonferroni correction factor of p less than 0.025. The work in this thesis determined the effects of changing stair climbing speed on lower extremity joint kinematics and kinetics. Joint angles were found to vary significantly for both ascending and descending stair trials, but less for descending. Internal joint flexion moments did not change significantly for ascending stairs, but were more varied in descending stairs. Peak ground reaction forces were found to vary significantly with speed and increased with speed. Average peak EMG activations and and activation timing was found to increase as speed increased, as well. The research conducted in this thesis is the preliminary work towards creating a normative database characterizing the effects of speed in ascending and descending stairs in healthy young adults. In the future, data from other populations, especially those with mobility disorders, can be compared with this normative database. Characterization of the biomechanics of stair climbing in individuals with disabilities may direct innovative rehabilitative therapies to target and strengthen impaired muscle groups so that these people can negotiate stairs with increased ease and independence.