High Capacity Older Adults Exhibit More Biomechanical Plasticity than Low Capacity Older Adults

Abstract

Old compared to young adults exhibit increased hip and decreased ankle joint work during level walking. This distal-to-proximal redistribution of joint work is known as biomechanical plasticity and is a successful strategy for maintaining walking performance into old age. It is unknown however whether high-functioning adults, (e.g. those with relatively fast walking speed) exhibit larger magnitudes of plasticity enabling them to walk well or whether low-functioning adults exhibit larger magnitudes of plasticity to simply enable them to walk. The literature weakly suggests that “low-performing” compared to “high-performing” old adults exhibit larger magnitudes of biomechanical plasticity. We seek to more precisely identify the nature of biomechanical plasticity with age and its relationship with physical capacity. PURPOSE: To compare magnitude of biomechanical plasticity between high and low capacity old adults during level walking. METHODS: 3D motion capture gait analyses were conducted on 30 old adults (n = 19 females; age = 74.7 yrs.) walking at self-selected speeds. Short Form Health Survey (SF-36) physical component scores were used as measures of physical capacity. Ratios of positive hip work to positive ankle work and peak positive hip extensor power to peak positive plantarflexor power were used as measures of biomechanical plasticity. Student’s t-tests were used to compare the top 10 (n = 8 females; age = 76.5 yrs.) and bottom 10 (n = 5 females; age = 72.8 yrs.) individuals based on their SF-36 PC scores. RESULTS: High capacity adults exhibited larger ratios of both hip/ankle positive work (0.948 vs 0.613, p = 0.01) and hip/ankle peak positive power (0.599 vs 0.375, p = 0.003) compared to low capacity adults. High capacity adults exhibited faster self-selected walking speed (1.39 vs 1.22 m/s, p = 0.01) and longer stride lengths (1.46 vs 1.29 m, p = 0.002) compared to low capacity adults. CONCLUSION: Old adults with high physical capacity exhibited a larger magnitude of biomechanical plasticity compared to old adults with low physical capacity. This allowed the high capacity individuals to maintain faster self-selected walking speeds and longer stride lengths compared to the low capacity individuals – two variables that may help these individuals maintain higher capacities.