Knee Extensor Capacity Utilization and Stair-gait Biomechanics in Younger and Older Adults

Abstract

Stair-gait is a more challenging task than level-gait, particularly for older adults. Both ascending and descending stairs require greater lower extremity joint ranges of motion, vertical ground reaction forces, and external knee flexion moments than level-gait. Safe and efficient performance while negotiating stairs is largely dependent on adequate knee extensor muscle function. However, age-related declines to muscle quantity, quality, and function contribute to limitations in physical function and independence during activities of daily living, such as stair-gait. Consequently, compensatory movement strategies employed by the trunk may be a key mechanism by which those with reduced muscle function adapt to large knee joint demands encountered in daily activity. The large demands imposed by stairs paired with reduced muscle function among a growing ageing population poses a substantial threat to quality of life. A few studies have investigated knee extensor muscle utilization, a concept that describes the proportion of the maximal available capacity of the knee extensors that is used to complete a task. Knee extensor muscle utilization is greater in older adults compared to younger adults during walking and other tasks. A number of studies also demonstrate knee extensor muscle capacity utilization is larger during stair ascent and descent compared to level walking in both young and older adults. However, little data compare knee extensor muscle capacity utilization between young and older adults on stair negotiation; and no study has determined whether this is related to sagittal plane trunk kinematics. This study aimed to compare knee extensor capacity utilization during stair ascent and descent in older adults versus younger adults. A secondary aim was to determine if this knee extensor capacity utilization is related to sagittal plane trunk kinematics. Twenty-five healthy young adults (n = 16) aged 18-30 years and healthy older adults (n = 9) aged 45-70 years were recruited primarily from the University of Waterloo and surrounding communities. Three-dimensional kinematics and kinetics were captured while participants ascended and descended a custom-built 4-step staircase using a high-speed motion capture system as well as floor- and step-embedded force plates, respectively. Knee extensor capacity utilization was calculated from maximal voluntary isometric and isokinetic contractions via dynamometry and peak external knee flexion moments measured in the stance phase of stair-gait for both stair ascent and descent. A two-tailed Welch’s t-test was used to determine if there was any difference in knee extensor capacity utilization between the healthy young adults and healthy older adults. A Pearson-Product Moment Correlation test was used to determine the relationship between knee extensor capacity utilization and the peak trunk flexion angle during the stance phase of stair-gait. Healthy older adults exhibited significantly greater knee extensor capacity utilization compared to healthy younger adults (p = 0.02), but not while descending stairs (p = 0.62). Knee extensor capacity utilization was not associated with peak sagittal trunk flexion angles during the stance phase of stair ascent (r = -0.06; p = 0.77) or stair descent (r = -0.31; p = 0.14). Findings demonstrate that healthy older adults utilize a greater amount of their available knee extensor capacity than healthy younger adults during stair ascent but not during stair descent. KECU was not associated with peak trunk flexion while either ascending or descending the stairs. Overall, findings further support for stair ascent being more challenging for older adults than younger adults. This study provides insight into the impact of knee extensor weakness while negotiating stairs.