How should the margin of stability during walking be expressed to account for body size?

When expressing the margin of stability as a distance, it does not directly estimate the perturbation magnitude needed to change stability states. Additionally, it is unknown how body size may influence this measure. Therefore, we propose other expressions of stability margins, including that of an impulse, a change in center of mass velocity, and a scaled, unitless impulse. The purpose of this study was to determine the influence of body size on these margin expressions using walking data from children and adults. We anticipated that margins expressed as an impulse would have strong correlations with body mass and height, as well as large between-group differences. We predicted that scaling this impulse value would result in small correlations and between-group effect sizes. We calculated each stability margin at minimum lateral values and in the anteroposterior directions at mid-swing and foot strike. In the lateral direction, margins expressed as an impulse had strong correlations with body size (r≥0.58, p<0.01) and large between-group differences (|d|≥1.07, p<0.01). The other expressions did not have strong positive correlations (|r|≤0.20) or large between-group effects (|d|≤0.44). In the anteroposterior directions, impulse margins had strong correlations with body size (|r|≥0.83, p<0.01) and large between-group differences (|d|≥1.74, p<0.01). The scaled, unitless impulse margin was the only variable that resulted in small, non-significant differences (|r|≤0.22, p≥0.24) as well as small between-group effect sizes (|d|≤0.46, p≥0.22). We propose expressing stability margins as an impulse. If scaling is needed, we encourage using the scaled, unitless impulse.

Kinematic analysis of speed transitions within walking in younger and older adults.

The ability to adapt to environmental and task demands while walking is critical to independent mobility outside the home and this ability wanes with age. Such adaptability requires individuals to acutely change their walking speed. Regardless of age, changes between walking speeds are common in daily life, and are a frequent type of walking adaptability. Here, we report on older and younger adults when transitioning from preferred walking speed overground to either slower or faster walking. Specifically, we evaluated biomechanical parameters prior to, during, and post transition. Individuals approached the walking speed transition similarly, independent of whether the transition was to slower or faster walking. Regardless of age or walking speed, the step during which a walking speed transition occurred was distinct from those prior- and post- transition, with on average 0.15 m shorter step lengths, 3.6° more hip flexion, and 3.3° more dorsiflexion during stance. We also found that peak hip flexion occurred 22% later, and peak hip extension (39%), knee flexion (26%), and dorsiflexion (44%) occurred earlier in stance for both typical to slower and typical to faster walking. Older adults had altered timing of peak joint angles compared with younger adults across both acceleration and deceleration conditions, indicating age-dependent responses to changing walking speed. Our findings are an important first step in establishing values for kinematics during walking speed transitions in younger and typical older adults.

Changes to margins of stability from walking to obstacle crossing in older adults while walking fast and with a dual-task.

It is not well understood how older adults meet the combined locomotor demands of obstacle avoidance at fast speeds as compared to obstacle avoidance under cognitive loads. The purpose of this study was to quantify changes in locomotor stability (margin of stability, MOS) from walking to crossing obstacles at fast speeds versus with added cognitive demands in older adults. Community-dwelling older adults walked on an unobstructed and obstructed path at their preferred speed (preferred); during a dualtask (verbal fluency); and at their 'fastest comfortable' speed (fast). We used motion capture to calculate MOS in the anteroposterior direction, and compared minimum MOS between crossing foot and support phase (lead single support, lead double support, trail single support, trail double support) and tested for within subject changes using a linear mixed effect regression model [Condition (preferred, fluency, fast) x Walkway (unobstructed, obstructed) x Phase (single support, double support) x Foot (lead, trail)]. We examined crossing kinematics (approach distance, toe clearance, and recovery distance) between conditions. A significant omnibus effect partially supported our predictions. A Condition x Walkway x Phase interaction supported that older adults increased stability under a cognitive load and prioritized stability, demonstrated by not changing MOS from walking to obstacle crossing. During fast obstacle crossing they decreased stability during double support and exhibit more stability in single support, when vulnerable to external perturbations (contacting the obstacle). During a dual-task, older adults took shorter and higher steps over the obstacle to ensure they cleared it safely, but at fast speeds they increased the length of their crossing step without higher toe clearance. The results suggest older adults attempt to preserve stability when crossing obstacles under both cognitive and speed demands, but may be unable to ensure a safer limb elevation to avoid obstacles at fast speeds as they do under cognitive demands.

Persons with Parkinson's disease show impaired interlimb coordination during backward walking.

INTRODUCTION: Although there is growing literature supporting the implementation of backward walking as a potential rehabilitation tool, moving backwards may precipitate falls for persons with Parkinson's disease. We sought to better understand interlimb coordination during backward walking in comparison to forward walking in persons with Parkinson's disease and healthy controls. METHODS: We assessed coordination using point estimate of relative phase at each participant's preferred walking speed. RESULTS: Persons with Parkinson's disease demonstrated impaired interlimb coordination between the more affected arm and each leg compared to controls, which worsened during backward walking. CONCLUSION: For those with Parkinson's disease, inability to output smooth coordinated movement of the more affected shoulder may impair coordination during forward and, especially, backward walking. Our findings provide new information about backward walking that can allow clinicians to make safer, more effective therapeutic recommendations for persons with Parkinson's disease.

Older women take shorter steps during backwards walking and obstacle crossing.

BACKGROUND: Community ambulation requires the ability to adapt walking patterns to task demands. For example, complex walking tasks, such as obstacle crossing (OBS) and backwards walking (BW), require modification of gait kinematics to complete the task, maintain stability and prevent falling. More women than men fall each year, but few studies have investigated gender differences in performance of adaptive walking tasks. OBJECTIVE: The purpose of this study was to determine gender differences in two common adaptive tasks. METHODS: Walking performance was assessed from 54 age and gender matched participants (72 ±â€¯5 yrs.) while they completed forward walking (FW), OBS and BW. Gait outcomes and the distance of the lead foot and the trail foot from the obstacle were normalized by leg length and assessed using multivariate analysis of variance. Additionally, performance in a battery of clinical physical and cognitive measures as well as self-reported activity levels were associated with adaptive gait behavior. RESULTS: Gait speed and step width were not different between genders in any walking task. Compared to FW and OBS, women only decreased step length in BW, resulting in significantly shorter step lengths than men in OBS (p = 0.02) and BW (p = 0.04), a conservative walking strategy. Women crossed the obstacle in a manner that may limit recovery steps in case of a trip: stepping closer to the obstacle during approach without increasing trail toe-clearance. The Timed Up and Go mobility test, Short Physical Performance Battery, and Trail Making Test of processing speed and executive function were associated with gender differences in adaptive gait patterns. CONCLUSION: The findings revealed that older adult women adapt walking in a way that might predispose them to tripping or falling (i.e. shorter steps and closer obstacle approach). Gender differences in adaptive walking are related to functional test performance and processing speed. Clinicians should consider targeting step length during adaptive walking tasks in women that may be at risk of mobility impairments.