Noah J. Rosenblatt

Variation in trunk kinematics influences variation in step width during treadmill walking by older and younger adults.

Step-by-step variations in step width have been hypothesized to reflect adjustments to swing foot placement in response to preceding frontal plane trunk kinematics. The present study tested this hypothesis while 12 younger and 11 older subjects walked on treadmill for 10min at a self-selected velocity. The relationship between step-by-step variations in step width and frontal plane trunk COM kinematics was determined using multiple regression analysis. Trunk kinematics at midstance were significantly (p<0.001) and strongly (R(2)=0.54) related to the subsequent foot placement supporting the primary hypothesis. Additionally, this relationship was significantly affected by age (p<0.001) and stepping limb (p<0.001). These results implicate feedback driven control of foot trajectory during the swing phase. Further, they provide a biomechanical framework by which loss of frontal plane dynamic stability may result from a step width that is insufficient to decelerate and redirect trunk kinematics in preparation for the next step.

Reliability of voluntary step execution behavior under single and dual task conditions

BackgroundThe current study investigated the repeatability (test-retest reliability) of ground reaction force parameters recorded during a voluntary step execution under single (motor task) and dual task (motor and cognitive task) conditions for healthy adults and elderly individuals as well as the number of trials required to produce repeatable results.MethodsTwenty-four healthy adults (21–63 years old) and 16 elderly adults (66–87 years) performed a voluntary rapid step execution following a tap on their heel while standing on a force platform under single and dual task conditions on three separate occasions. The first two tests were performed 30–60 minutes apart and the third test was performed a week later. Variables analyzed from the ground reaction force data included onset latency of step initiation (initiation phase), preparation and swing phases, foot-off and foot-contact times.ResultsIntraclass correlation coefficients (ICC(2,1)) were good to excellent across all parameters and test conditions for the pooled population and for elderly (0.74–0.92 and 0.62–0.88, respectively) except for the swing phase duration where lower values were seen (0.54–0.60 and 0.32–0.64 respectively). Values were similar under single and dual task conditions.ConclusionA voluntary step execution test, performed under single and dual task conditions especially foot-off and foot-contact times, is a reliable outcome measure that may be a useful tool to asses dynamic balance function for diagnostic purposes as well as clinical intervention trials.

Preventing Trip-Related Falls by Community-Dwelling Adults:: A Prospective Study

Conflict of Interest: Dr. Lin was supported by a grant from the National Institutes of Health (1K23DC011279), a Triological Society/American College of Surgeons Clinician Scientist Award, and the Eleanor Schwartz Charitable Foundation. Dr. Lin has served as a consultant to Cochlear Corp and Autifony, serves on the scientific advisory board for Autifony, and is speaker for Amplifon and Cochlear Corp. Author Contributions: All authors contributed to the study concept and design, analysis and interpretation of data, and preparation of the final manuscript. Sponsor’s Role: None.

Relationship between obesity and falls by middle-aged and older women

It has been suggested that obesity increases fall risk, based on diminished static balance and increased fall-related injury risk. However, these findings only indirectly relate obesity and falls. The purpose of this study was to use existing data to directly explore the relationship between obesity and falls by community-dwelling women aged 55 years and older. Eighty-six subjects (42 obese) reported falls occurring during the previous year (retrospective falls), and over the following year responded to biweekly communications inquiring whether they fell or stumbled (prospective falls/stumbles). Because trips represent the largest fall cause by community-dwelling adults, we also analyzed outcomes and recovery strategies of 25 women (13 obese) after laboratory-induced trips. Obese and healthy weight women retrospectively reported similar fall rates (40.9% vs 40.5%; P=.97). Similar percentages of healthy weight and obese women prospectively fell (64.7% vs 64.3%; P=.98) and stumbled (38.9% vs 14.3%; P=.24). After laboratory-induced trips, 46.2% of obese verse 25.0% of healthy weight women fell (P=.44). Unlike healthy weight fallers, most obese fallers failed to initiate or complete the recovery step before full-body harness support. Obesity does not appear to increase overall fall risk; although, fall rates after laboratory-induced trips were notably higher, potentially due to altered recovery responses. An incomplete recovery step could increase impact force with the ground, predisposing obese individuals to injury. The fact that there is concurrence between 4 independent outcomes strengthens the findings, suggesting that further, large-scale studies are warranted to inform future clinical practice regarding fall-risk assessment for obese older adults.

An apparent contradiction: increasing variability to achieve greater precision?

To understand the relationship between variability of foot placement in the frontal plane and stability of gait patterns, we explored how constraining mediolateral foot placement during walking affects the structure of kinematic variance in the lower-limb configuration space during the swing phase of gait. Ten young subjects walked under three conditions: (1) unconstrained (normal walking), (2) constrained (walking overground with visual guides for foot placement to achieve the measured unconstrained step width) and, (3) beam (walking on elevated beams spaced to achieve the measured unconstrained step width). The uncontrolled manifold analysis of the joint configuration variance was used to quantify two variance components, one that did not affect the mediolateral trajectory of the foot in the frontal plane (“good variance”) and one that affected this trajectory (“bad variance”). Based on recent studies, we hypothesized that across conditions (1) the index of the synergy stabilizing the mediolateral trajectory of the foot (the normalized difference between the “good variance” and “bad variance”) would systematically increase and (2) the changes in the synergy index would be associated with a disproportionate increase in the “good variance.” Both hypotheses were confirmed. We conclude that an increase in the “good variance” component of the joint configuration variance may be an effective method of ensuring high stability of gait patterns during conditions requiring increased control of foot placement, particularly if a postural threat is present. Ultimately, designing interventions that encourage a larger amount of “good variance” may be a promising method of improving stability of gait patterns in populations such as older adults and neurological patients.

The discriminant capabilities of stability measures, trunk kinematics, and step kinematics in classifying successful and failed compensatory stepping responses by young adults

This study evaluated the discriminant capability of stability measures, trunk kinematics, and step kinematics to classify successful and failed compensatory stepping responses. In addition, the shared variance between stability measures, step kinematics, and trunk kinematics is reported. The stability measures included the anteroposterior distance (d) between the body center of mass and the stepping limb toe, the margin of stability (MOS), as well as time-to-boundary considering velocity (TTB(v)), velocity and acceleration (TTB(a)), and MOS (TTB(MOS)). Kinematic measures included trunk flexion angle and angular velocity, step length, and the time after disturbance onset of recovery step completion. Fourteen young adults stood on a treadmill that delivered surface accelerations necessitating multiple forward compensatory steps. Thirteen subjects fell from an initial disturbance, but recovered from a second, identical disturbance. Trunk flexion velocity at completion of the first recovery step and trunk flexion angle at completion of the second step had the greatest overall classification of all measures (92.3%). TTB(v) and TTB(a) at completion of both steps had the greatest classification accuracy of all stability measures (80.8%). The length of the first recovery step (r ≤ 0.70) and trunk flexion angle at completion of the second recovery step (r ≤ -0.54) had the largest correlations with stability measures. Although TTB(v) and TTB(a) demonstrated somewhat smaller discriminant capabilities than trunk kinematics, the small correlations between these stability measures and trunk kinematics (|r| ≤ 0.52) suggest that they reflect two important, yet different, aspects of a compensatory stepping response.

Exercise-based fall prevention: can you be a bit more specific?

Trip-specific perturbation training reduces trip-related falls after laboratory-induced trips and, prospectively, in the community. Based on an emerging body of evidence, we hypothesize that using task-specific perturbation training as a stand-alone approach or in conjunction with conventional exercise-based approaches will improve the effectiveness of fall prevention interventions significantly.

The effects of age on stabilization of the mediolateral trajectory of the swing foot

To ensure stability during gait, mediolateral placement of the swinging foot must be actively regulated. Logically this occurs through end-point control of the swing limb trajectory, the precision of which is quantified as step-width variability (SWV). Increased SWV with age may reflect reduced precision of this control, but cannot describe if, and how, age-related changes in lower limb kinematic synergies account for reduced precision. We analyzed joint configuration variance across steps within the uncontrolled manifold (UCM) hypothesis, which assumes that redundant sets of elemental variables are organized by the central nervous system to stabilize important performance variables. We tested whether: (1) regardless of age, the swing limb trajectory would be stabilized by a kinematic synergy of the lower limbs, and (2) the strength of the synergy would be weaker in older adults. Ten younger and ten older adults (65+ years) walked on a laboratory walkway at their preferred speed while kinematic data were collected. UCM analysis of segmental configuration variance was performed with respect to the mediolateral trajectory of the swing-limb ankle joint center. Throughout most of swing, the trajectory was stabilized by a kinematic synergy. Despite the greater segmental configuration variance of older adults, the strength of the synergy was not significantly different between groups. Moreover, the synergy index became negative during terminal swing and was not significantly correlated with SWV. Accordingly, co-variation among individual segmental trajectories is more important for stabilization of the swing trajectory during mid-swing, and, throughout swing, aging does not appear to affect this stabilization.

Active dorsiflexing prostheses may reduce trip-related fall risk in people with transtibial amputation

People with amputation are at increased risk of falling compared with age-matched, nondisabled individuals. This may partly reflect amputation-related changes to minimum toe clearance (MTC) that could increase the incidence of trips and fall risk. This study determined the contribution of an active dorsiflexing prosthesis to MTC. We hypothesized that regardless of speed or incline the active dorsiflexion qualities of the ProprioFoot would significantly increase MTC and decrease the likelihood of tripping. Eight people with transtibial amputation walked on a treadmill with their current foot at two grades and three velocities, then repeated the protocol after 4 wk of accommodation with the ProprioFoot. A mixed-model, repeated-measures analysis of variance was used to compare MTC. Curves representing the likelihood of tripping were derived from the MTC distributions and a multiple regression was used to determine the relative contributions of hip, knee, and ankle angles to MTC. Regardless of condition, MTC was approximately 70% larger with the ProprioFoot (p < 0.001) and the likelihood of tripping was reduced. Regression analysis revealed that MTC with the ProprioFoot was sensitive to all three angles, with sensitivity of hip and ankle being greater. Overall, the ProprioFoot may increase user safety by decreasing the likelihood of tripping and thus the pursuant likelihood of a fall.

Obesity as a factor contributing to falls by older adults

The growth of the worldwide population of older adults presents significant challenges, many inter-related, that range from the health of individuals to the health of national economies. In the US, more than one-third of older adults may be obese, a condition that may independently increase the risk for mobility impairment, fall-related injury and, possibly, costs of post-injury treatment and care. The effectiveness of conventional exercise-based fall prevention programs is significant but smaller than both the annual rate of falling of older adults and rate of growth of this population, who are at greatest risk for injurious falls. The anthropometric and functional consequences of obesity may impose limitations on the ability to perform compensatory stepping responses following large postural disturbances. The focus of this paper is the potential of task-specific training to improve compensatory stepping responses and reduce falls by obese people given the individual-specific anthropometric and functional consequences of obesity.