Aging gait

The Functional Utilization of Propulsive Capacity During Human Walking

The age-associated decline in propulsive push off power generated during walking plays a central role in the reduction of mobility and independence in older adults. Previous work suggests that this population retains an underutilized propulsive reserve during normal walking that dynamometry assessments fail to effectively assess. This is especially notable when assessing plantarflexor mechanical output, which often yield implausible (i.e., ≥100%) values of ‘functional capacity utilized (FCU)’, most frequently defined as the ratio of the peak ankle moment during the push-off phase of walking to that during a maximum isometric voluntary contraction. Therefore, the extent to which we utilize our propulsive capacity, how utilization changes as we age, and the factors that govern utilization and maximum propulsive capacity remain unclear. Utilizing a feedback controlled, motor driven horizontal impeding force system and a novel maximum force condition which systematically increases applied force, we can find a participant’s maximum propulsive capacity. During this condition, we find that younger adults retain a reserve of 48% in terms of ground reaction force, 22% in terms of ankle moment and 43% in terms of ankle power, which may not be effectively predicted using dynamometry assessments. As an important first step, we present data showing that a more functional task, walking with horizontal impeding forces, could potentially more effectively assess propulsive reserves in younger adults.
Listed In: Biomechanics

The relationships between physical capacity and biomechanical plasticity in old adults during level and incline walking

Old versus young adults exhibit increased hip and decreased ankle joint mechanical output during level and incline walking. This distal-to-proximal redistribution of joint torques and powers is now a well-established age-related gait adaptation and has been termed biomechanical plasticity. The effect of physical capacity, which varies greatly in old adults, on this gait adaptation remains unclear. For example, high capacity old adults (i.e. those with fast walking speeds) might either retain a more youthful gait strategy or adopt larger magnitudes of plasticity in order to walk well. The purpose of this study was to quantify the relationships between physical capacity and biomechanical plasticity in old adults during level and incline walking. We conducted 3D gait analyses on 32 old adults (>70 yrs) as they walked over level ground and up a 10° incline at self-selected speeds. We used motion capture (Qualisys AB) and force platforms (AMTI) to collect kinematic and ground reaction force data, respectively. To measure physical capacity, we used the SF-36 Physical Component score and to define biomechanical plasticity we created ratios of hip extensor to ankle plantarflexor peak torques, angular impulses, peak positive powers, and work. We conducted correlation analyses between SF-36 PC scores and the biomechanical plasticity ratios. Positive relationships existed between SF-36 PC scores and all biomechanical plasticity ratios during level walking. Similar results were observed during incline walking, however only three of these four relationships reached statistical significance. Our results suggest that old adults of higher physical capacities exhibit larger magnitudes of biomechanical plasticity.
Listed In: Biomechanics, Gait

The effect of fatigue on knee mechanics in older adults: Does physical activity matter?

INTRODUCTION. Increased age is associated with changes in gait mechanics and decreased muscle function. As the knee extensors (KE) are prime movers in gait, altered KE function (strength, power, fatigability) could alter knee mechanics. This study aimed to determine whether a bout of exercise induces KE fatigue and changes in knee mechanics in two older groups with different physical activity levels: sedentary adults and runners. METHODS. Adults aged 55-70 who were either runners (≥15 miles/wk) or sedentary (≤3x30 min exercise bouts/wk) completed gait and strength testing before and after a 30 minute treadmill walk (30MTW). Joint kinematics were calculated using the point cluster technique. Externally-referenced moments were calculated using inverse dynamics. KE power and isometric strength were assessed via isokinetic dynamometry. Changes in KE power and knee mechanics were calculated; within-group changes were examined using paired t-tests (p<0.1). RESULTS. Sedentary adults displayed a drop in KE power at 6/8 contraction velocities vs. 2/8 in runners (poster Figure 2). Both groups showed an increase in knee flexion angle at heel strike and runners displayed decreased knee flexion moments post-30MTW (poster Figure 3). CONCLUSIONS. Vigorous physical activity may allow older adults to maintain fatigue resistance. Sensitivity of knee mechanics to KE fatigue remains unclear as few changes were seen even in a fatigued group. Global, rather than discrete, measures of joint function may provide more sensitive measures of the response of gait mechanics to muscle fatigue and may allow for a more complete picture of the impact of muscle function on gait.
Listed In: Biomechanics, Gait