Increased Stance Phase Knee Flexion During Gait May Support Smooth Step-to-step Transitions In Older Adults

Energy conservation and smooth transition are two important facets of functional gait (Baker, 2009). Jerk as the first derivative of acceleration quantifies the smoothness of a trajectory. Stein, 1986, argued that minimizing walking energy cost is related to minimizing jerk. But Hreljac, 1993, found smoothness and economy were negatively correlated during walking. The step-to-step transition costs play a major role in the metabolic cost of walking (Kuo, 2002 & 2005) and smooth transition involves the stance phase knee flexion mechanism which interrupts the pendulum like motion of the leg and costs energy (Baker, 2009). Aging leads to larger knee flexion during the step-to-step transition and rising energy cost (Boyer et al., 2017; Wert et al., 2013). We hypothesized that age-related increase in stance phase knee flexion is to facilitate smooth transition which might prioritize smoothness over economy in older adults’ gait. PURPOSE: To compare knee angular jerk (KAJ) between young and older adults at preferred gait speeds. METHODS: 10 young (age: 25.2 ± 3.25 years, weight: 74.08 ± 12.27 kg, height: 1.72 ± 0.83 m, gait speed: 1.32 ± 0.10 m/s) and 10 older (age: 70.57 ± 3.50 years, weight: 71.03 ± 13.42 kg, height: 1.71 ± 0.14 m, gait speed: 1.33 ± 0.18 m/s) healthy adults walked on a treadmill, while ten-camera Vicon motion capture and Conventional Gait Model 2.4 were used to record and calculate knee motion. KAJ was calculated as first derivative of acceleration for a hundred gait cycles for each participant. SPM with t-test was used to compare KAJ between groups. RESULTS: Despite increase in stance knee flexion in older adults, KAJ did not differ significantly between groups (Figure 1). CONCLUSION: Increase in stance knee flexion in older adults without significant differences in KAJ between groups could indicate older adults prioritize a smooth transition rather than energy conservation.