The Relationships Between Physical Capacity And Biomechanical Plasticity With Age During Level And Incline Walking

Abstract

Old compared to young adults exhibit a distal-to-proximal redistribution of joint contributions to support phase mechanics during level and incline walking. Although this biomechanical plasticity is now well established in healthy old adults, less is known about how biomechanical plasticity varies across the physical capacity spectrum in this population. For example, it is unclear whether high capacity old adults (i.e. individuals with relatively high walking performance) retain a more youthful gait strategy (i.e. low magnitudes of biomechanical plasticity) or adopt larger magnitudes of biomechanical plasticity in order to walk well. The purpose of my thesis was to examine and quantify the relationships between physical capacity and biomechanical plasticity in old adults during level and incline walking. We hypothesized that, as physical capacity declines, biomechanical plasticity would increase in magnitude. We also hypothesized that the magnitude of change in biomechanical plasticity per unit change in physical capacity would be greater during the more challenging task of incline compared to level walking. To test these hypotheses, we performed gait analyses on 10 young and 32 old adults as they walked over level and inclined (+10°) surfaces at self-selected and controlled speeds. We used Short-Form Health Survey Physical Component (SF-36 PC) scores and 20-meter self-selected speeds as measures of physical capacity. To quantify biomechanical plasticity, we created ratios of hip extensor to ankle plantarflexor peak torques, angular impulses, peak positive powers, and positive work. Compared to young adults, old adults exhibited larger biomechanical plasticity ratios during all four walking conditions - confirming the existence of age-associated biomechanical plasticity in the old adults included in this study. Contrary to our hypothesis, correlation analyses revealed positive relationships between physical capacity and biomechanical plasticity during level and incline walking at self-selected but not controlled speeds. Positive relationships between in-trial self-selected speeds during level walking suggest that increased magnitudes of biomechanical plasticity might positively influence walking performance. Contrary to our second hypothesis, incline walking did not increase magnitude of biomechanical plasticity change per unit change in physical capacity. Our results suggest that age-associated biomechanical plasticity represents a beneficial gait adaptation that might afford functional benefits such as increased walking speed. Results from our cross-sectional design may provide the framework for a longitudinal intervention study aimed at increasing biomechanical plasticity and thereby walking performance in old adults. Increased walking performance in this population has the potential to decrease adverse outcomes such as falls, hospitalizations, and even mortality, leading to an overall increased quality of life.