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.

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.

Task-specific fall prevention training is effective for warfighters with transtibial amputations.

BACKGROUND: Key factors limiting patients with lower extremity amputations to achieve maximal functional capabilities are falls and fear of falling. A task-specific fall prevention training program has successfully reduced prospectively recorded trip-related falls that occur in the community by the elderly. However, this program has not been tested in amputees. QUESTIONS/PURPOSES: In a cohort of unilateral transtibial amputees, we aimed to assess effectiveness of a falls prevention training program by (1) quantifying improvements in trunk control; (2) measuring responses to a standardized perturbation; and (3) demonstrating retention at 3 and 6 months after training. Second, we collected patient-reported outcomes for balance confidence and falls control. METHODS: Fourteen male military service members (26 ± 3 years) with unilateral transtibial amputations and who had been walking without an assistive device for a median of 10 months (range, 2-106 months) were recruited to participate in this prospective cohort study. The training program used a microprocessor-controlled treadmill designed to deliver task-specific postural perturbations that simulated a trip. The training consisted of six 30-minute sessions delivered over a 2-week period, during which task difficulty, including perturbation magnitude, increased as the patient's ability progressed. Training effectiveness was assessed using a perturbation test in an immersive virtual environment. The key outcome variables were peak trunk flexion and velocity, because trunk kinematics at the recovery step have been shown to be a determinant of fall likelihood. The patient-reported outcomes were also collected using questionnaires. The effectiveness of the rehabilitation program was also assessed by collecting data before perturbation training and comparing the key outcome parameters with those measured immediately after perturbation training (0 months) as well as both 3 and 6 months posttraining. RESULTS: Mean trunk flexion angle and velocity significantly improved after participating in the training program. The prosthetic limb trunk flexion angle improved from pretraining (42°; 95% confidence interval [CI], 38°-47°) to after training (31°; 95% CI, 25°-37°; p < 0.001). Likewise, the trunk flexion velocity improved from pretraining (187°/sec; 95% CI, 166°-209°) to after training (143°/sec; 95% CI, 119°-167°; p < 0.004). The results display a significant side-to-side difference for peak trunk flexion angle (p = 0.01) with perturbations of the prosthetic limb resulting in higher peak angles. Prosthetic limb trips also exhibited significantly greater peak trunk flexion velocity compared with trips of the prosthetic limb (p = 0.005). These changes were maintained up to 6 months after the training. The peak trunk flexion angle of the subjects when the prosthetic limb was perturbed had a mean of 31° (95% CI, 25°-37°) at 0 month, 32° (95% CI, 28°-37°) at 3 months, and 30° (95% CI, 25°-34°) at 6 months. Likewise, the peak trunk flexion velocity for the prosthetic limb was a mean of 143°/sec (95% CI, 118°-167°) at 0 months, 143°/sec (95% CI, 126°-159°) at 3 months, and 132° (95% CI, 115°-149°) at 6 months. The peak trunk flexion angle when the nonprosthetic limb was perturbed had a mean of 22° (95% CI, 18°-24°) at 0 months, a mean of 26° (95% CI, 20°-32°) at 3 months, and a mean of 23° (95% CI, 19°-28°) at 6 months. The peak trunk flexion velocity for the nonprosthetic limb had a mean of 85°/sec (95% CI, 71°-98°) at 0 months, a mean of 96° (95% CI, 68°-124°) at 3 months, and 87°/sec (95% CI, 68°-105°) at 6 months. There were no significant changes in the peak trunk flexion angle (p = 0.16) or peak trunk flexion velocity (p = 0.35) over time after the training ended. The skill retention was present when either the prosthetic or nonprosthetic limb was perturbed. There were side-to-side differences in the trunk flexion angle (p = 0.038) and trunk flexion velocity (p = 0.004). Perturbations of the prosthetic side resulted in larger trunk flexion and higher trunk flexion velocities. Subjects prospectively reported decreased stumbles, semicontrolled falls, and uncontrolled falls. CONCLUSIONS: These results indicate that task-specific fall prevention training is an effective rehabilitation method to reduce falls in persons with lower extremity transtibial amputations.

Fall Prevention Training for Service Members With an Amputation or Limb Salvage Following Lower Extremity Trauma.

INTRODUCTION: Recent military conflicts have resulted in a significant number of lower extremity injuries to U.S. service members that result in amputation or limb preservation (LP) procedures. Service members receiving these procedures report a high prevalence and deleterious consequences of falls. Very little research exists to improve balance and reduce falls, especially among young active populations such as service members with LP or limb loss. To address this research gap, we evaluated the success of a fall prevention training program for service members with lower extremity trauma by (1) measuring fall rates, (2) quantifying improvements in trunk control, and (3) determining skill retention at 3 and 6 months after training. MATERIALS AND METHODS: Forty-five participants (40 males, mean [±SD] age, 34 ± 8 years) with lower extremity trauma (20 with unilateral transtibial amputation, 6 with unilateral transfemoral amputation, 5 with bilateral transtibial amputation, and 14 with unilateral LP procedures) were enrolled. A microprocessor-controlled treadmill was used to produce task-specific postural perturbations which simulated a trip. The training was conducted over a 2-week period and consisted of six 30-minute sessions. The task difficulty was increased as the participant's ability progressed. The effectiveness of the training program was assessed by collecting data before training (baseline; repeated twice), immediately after training (0 month), and at 3 and 6 months post-training. Training effectiveness was quantified by participant-reported falls in the free-living environment before and after training. Perturbation-induced recovery step trunk flexion angle and velocity was also collected. RESULTS: Participants reported reduced falls and improved balance confidence in the free-living environment following the training. Repeated testing before training revealed that there were no pre-training differences in trunk control. The training program improved trunk control following training, and these skills were retained at 3 and 6 months after training. CONCLUSION: This study showed that task-specific fall prevention training reduced falls across a cohort of service members with diverse types of amputations and LP procedures following lower extremity trauma. Importantly, the clinical outcome of this effort (i.e., reduced falls and improved balance confidence) can lead to increased participation in occupational, recreational, and social activities and thus improved quality of life.

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.

Sensitivity of dynamic stability to changes in step width during treadmill walking by young adults.

Recent experimental findings support theoretical predictions that across walking conditions the motor system chooses foot placement to achieve a constant minimum "margin of stability" (MOSmin)--distance between the extrapolated center of mass and base of support. For example, while step width varies, similar average MOSmin exists between overground and treadmill walking and between overground and compliant/irregular surface walking. However, predictions regarding the invariance of MOSmin to step-by-step changes in foot placement cannot be verified by average values. The purpose of this study was to determine average changes in, and the sensitivity of MOSmin to varying step widths during two walking tasks. Eight young subjects walked on a dual-belt treadmill before and after receiving information that stepping on the physical gap between the belts causes no adverse effects. Information decreased step width by 17% (p = .01), whereas MOSmin was unaffected (p = .12). Regardless of information, subject-specific regressions between step-by-step values of step width and MOSmin explained, on average, only 5% of the shared variance (ß = 0.11 ± 0.05). Thus, MOSmin appears to be insensitive to changing step width. Accordingly, during treadmill walking, step width is chosen to maintain MOSmin. If MOSmin remains insensitive to step width across other dynamic tasks, then assessing an individual's stability while performing these tasks could help describe the health of the motor system.

Military training alters the fractal behavior of step width.

Non-linear analyses have been successfully applied to gait with evidence that fractal behavior of gait-related variables provide insights into function. Specifically, shifts in the fractal behavior of step width from pink toward white noise reflects a loss of complexity and diminished adaptive capacity and functionality. We previously reported an apparent difference in the fractal behavior of step width during treadmill walking between Service members with transtibial amputations and able-bodied civilian. We now combine recently collected data and data from two previous studies to further explore the relationship between lower limb injury, military service, and step width fractal behavior. Service member, regardless of the presence or type of injury, demonstrate step width fractal behavior walked in a way that the fractal behavior of their gait was significantly closer to white noise (-0.5 dB/Hz2) than uninjured civilians (-0.82 dB/Hz2). This data suggests that military training/service leads to a change in step width fractal behavior. Further studies are needed to explore what may cause this difference and any implications this may have on stability or performance.

Common fall-risk indicators are not associated with fall prevalence in a high-functioning military population with lower limb trauma.

BACKGROUND: Persons with lower limb trauma are at high risk for falls. Although there is a wide range of measures used to assess stability and fall-risk that include performance measures, temporal-spatial gait parameters, and nonlinear dynamic stability calculations, these measures are typically derived from fall-prone populations, such as older adults. Thus, it is unclear if these commonly used fall-risk indicators are effective at evaluating fall-risk in a younger, higher-functioning population of Service members with lower limb trauma. METHODS: Twenty-one Service members with lower limb trauma completed a battery of fall-risk assessments that included performance measures (e.g., four-square-step-test), and gait parameters (e.g., step width, step length, step time) and dynamic stability measures (e.g., local divergence exponents) during 10 min of treadmill walking. Participants also reported the number of stumbles and falls over the previous 4 weeks. Negative Binomial and Quasibinomial Regressions were used to evaluate the strength of associations between fall-risk indicators and self-reported falls. FINDING: Participants reported on average stumbling 6(4) times and falling 2(3) times in the previous 4 weeks. At least one fall was reported by 62% of the participants. None of the fall-risk indicators were significantly associated with fall prevalence in this population of Service members with lower limb trauma (p > 0.1). INTERPRETATION: Despite the high number of reported falls in this young active population, none of the fall-risk indicators investigated effectively captured and quantified the fall-risk. Further research is needed to identify appropriate fall-risk assessments for young, high-functioning individuals with lower limb trauma.

Assessments of trunk postural control within a fall-prevention training program for service members with lower limb trauma and loss.

BACKGROUND: Trunk postural control (TPC) is critical in maintaining balance following perturbations (i.e., avoiding falls), and impaired among persons with lower extremity trauma, contributing to elevated fall risk. Previously, a fall-prevention program improved TPC in individuals with unilateral transtibial amputation following trip-inducing perturbations. However, it is presently unclear if these improvements are task specific. RESEARCH QUESTION: Do improvements to TPC gained from a fall-prevention program translate to another task which assesses TPC in isolation (i.e., unstable sitting)? Secondarily, can isolated TPC be used to identify who would benefit most from the fall-prevention program? METHODS: Twenty-five individuals (21 male/4 female) with lower extremity trauma, who participated in a larger fall-prevention program, were included in this analysis. Trunk flexion and flexion velocity quantified TPC following perturbation; accelerometer-based sway parameters quantified TPC during unstable sitting. A generalized linear mixed-effects model assessed training-induced differences in TPC after perturbation; a generalized linear model assessed differences in sway parameters following training. Spearman's rho related training-induced changes to TPC following perturbation (i.e., the difference in TPC measures at pre- and post-training assessments) with pre- vs. post-training changes to sway parameters during unstable sitting (i.e., the difference in sway parameters at pre- and post-training assessments) as well as pre-training sway parameters with the pre- vs. post-training differences in TPC following perturbation. RESULTS: Following training, trunk flexion angles decreased, indicating improved TPC; however, sway parameters did not differ pre- and post-training. In addition, pre- vs. post-training differences in TPC following perturbation were neither strongly nor significantly correlated with sway parameters. Moreover, pre-training sway parameters did not correlate with pre- vs. post-training differences in trunk flexion/flexion velocity. SIGNIFICANCE: Overall, these results indicate that improvements to TPC gained from fall-prevention training are task-specific and do not translate to other activities. Moreover, isolated TPC measures are not able to identify individuals that benefit most from the fall-prevention program.

Form of the compensatory stepping response to repeated laterally directed postural disturbances.

A compensatory stepping response (CSR) is a common strategy to restore dynamic stability in response to a postural disturbance. Currently, few studies have investigated the CSR to laterally directed disturbances delivered to subjects during quiet standing. The purpose of this study was to characterize the CSR of younger adults following exposure to a series of similar laterally directed disturbances for which no instructions were given with regard to the recovery response. We hypothesized that in the absence of externally applied constraints to the recovery response, subjects would be equally as likely to perform a crossover step as a sidestep sequence (SSS). We further hypothesized that there would be an asymmetry in arm abduction that would be dependent on the disturbance direction. Finally, we were interested in characterizing the effect of practice on the CSR to repeated disturbances. Ten younger adults were exposed to thirty laterally directed platform disturbances that forced a stepping response. Subjects responded by primarily utilizing a SSS that differs from previously reported results. Further, five of the ten subjects utilized a different recovery response that was dependent on the direction of the disturbance (i.e., left or right). Greater arm abduction was characterized for the arm in the direction of the external disturbance in comparison with the contralateral arm. Lastly, subjects modified their recovery response to this task within 12 disturbances. Taken together, these results suggest that recovery responses to laterally directed disturbances can be quickly modified but can be quite variable between and within subjects.

Fear of falling does not alter the kinematics of recovery from an induced trip: a preliminary study.

OBJECTIVE: To provide preliminary information about the relationships between self-reported fear of falling (FOF) in healthy community-dwelling women, number of falls, and recovery kinematics in response to a laboratory-induced trip. DESIGN: Cohort study. SETTING: Clinical research laboratory. PARTICIPANTS: A subset of community-dwelling older women (N=33) recruited from studies of laboratory-induced trips and fall prevention. INTERVENTION: A laboratory-induced trip. MAIN OUTCOME MEASURES: Number of fallers in the FOF group versus the control group. Recovery kinematics of FOF group falls versus control group falls, and FOF group recoveries versus control group recoveries were compared. Degree of FOF was assessed by using the Activities-Specific Balance Confidence (ABC) Scale. RESULTS: Falls occurred in 6 of 14 (43%) FOF and 4 of 16 (25%) control subjects (P=.26). The kinematics of FOF group falls were similar to those of control group falls. At completion of the initial recovery step, the FOF group showed significantly greater trunk extension velocity than controls (-82.1°/s ± -66.1°/s vs -25.0°/s ± -53.0°/s, respectively; P=.05). All other variables were not significantly different. ABC Scale scores of FOF subjects did not differ significantly between fallers and those who recovered (mean, 75.2 ± 5.6, 71.1 ± 11.8, respectively; P=.84). CONCLUSION: Healthy community-dwelling older adults would benefit from fall prevention regardless of the presence of self-reported FOF.

Developing and Establishing Biomechanical Variables as Risk Biomarkers for Preventable Gait-Related Falls and Assessment of Intervention Effectiveness.

The purpose of this review is to position the emerging clinical promise of validating and implementing biomechanical biomarkers of falls in fall prevention interventions. The review is framed in the desirability of blunting the effects of the rapidly growing population of older adults with regard to the number of falls, their related injuries, and health care costs. We propose that biomechanical risk biomarkers may be derived from systematic study of the responses to treadmill-delivered perturbations to both identify individuals with a risk of specific types of falls, such as trips and slips as well as quantifying the effectiveness of interventions designed to reduce that risk. The review follows the evidence derived using a specific public health approach and the published biomedical literature that supports trunk kinematics as a biomarker as having met many of the criteria for a biomarker for trip-specific falls. Whereas, the efficacy of perturbation training to reduce slip-related falls by older adults appears to have been confirmed, its effectiveness presently remains an open and important question. There is a dearth of data related to the efficacy and effectiveness of perturbation training to reduce falls to the side falls by older adults. At present, efforts to characterize the extent to which perturbation training can reduce falls and translate the approaches to the clinic represents an important research opportunity.

Treadmill-belt width, but not feedback from the lower visual field, influences the noise characteristics of step width time series.

Step kinematic variability, which has been associated with gait-related fall risk, is thought to be attributed to neuromotor noise. Altered neuromotor control of step kinematics would be expected to manifest as changes in the noise-related characteristics of the step kinematic time series. This study determined the effects of eliminating feedback from the lower visual field and reducing treadmill-belt width on the noise characteristics of step width time series and statistical measures of step width variability during treadmill walking. We hypothesized that eliminating feedback from the lower visual field and reducing treadmill-belt width would both alter the noise characteristics of step width time series, reflected by decreased fractal scaling, and increase statistical measures of step width variability. Eighteen young adults performed four randomly ordered walking trials during which we manipulated visual feedback from the lower visual field (normal and obstructed) and treadmill-belt width (wide and narrow). Reducing treadmill-belt width, but not eliminating feedback from the lower visual field, significantly reduced the fractal scaling of step width time series, indicating a shift towards white, uncorrelated noise. These results suggest that accounting for the influence of treadmill-belt width on step width time series may be an important consideration in both laboratory and clinical settings. Further work is needed to clarify the effects of vision on measures of step width, identify the mechanism(s) underlying the observed shift towards white, uncorrelated noise associated with reduced treadmill-belt width, and to assess the potential relationship between the noise characteristics of step width time series and fall risk.

Task-Specific Perturbation Training Improves the Recovery Stepping Responses by Women With Knee Osteoarthritis Following Laboratory-Induced Trips.

Trip-specific training improves the kinematics of trip-specific compensatory stepping response (CSR) in the laboratory and reduces prospectively measured trip-related fall-rate of middle age and older women. We examined whether one session of trip-specific perturbation training could improve recovery step kinematics in women with knee osteoarthritis (OA), a condition known to increase fall risk. Seventeen women with self-reported symptomatic knee OA (age 61.1 ± 7.7 years, body mass index [BMI] 29.7 ± 5.9 kg/m2 ) and 22 control women (age 59.5 ± 6.8 years, BMI 28.4 ± 6.2 kg/m2 ) completed a brief training protocol consisting of 20 trials of treadmill-delivered trip-specific perturbations. We assessed pre- and post-training recovery step length and trunk kinematics at the instant of recovery step completion. Repeated-measures analysis of variance was used to determine the significance of between-group differences following the training protocol, and to evaluate the significance of within-group pre-to-post changes in the variables of interest. The group by training interaction effects for step length (p = 0.466), trunk flexion angle (p = 0.751), and trunk angular velocity (p = 0.413) were not significant and the pre-to-post changes in step length were not significant (p = 0.286). However, pre-to-post trunk flexion angle improved by 26% and 34% in the OA and control groups, respectively (p < 0.001) and trunk flexion angular velocity decreased by 193% in the OA group and by 32% in the control group, respectively (p < 0.001), often reflecting a transition to the direction of extension. The results suggest that trip-specific training can improve CSR kinematics in women with knee OA. It is important to determine, the effectiveness of trip-specific training in decreasing trip-specific fall-rate by women with knee OA. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:663-669, 2020.

A single session of trip-specific training modifies trunk control following treadmill induced balance perturbations in stroke survivors.

BACKGROUND: Individuals with stroke are at significant risk of falling. Trip-specific training is a targeted training approach that has been shown to reduce falls in older adults and amputees by enhancing the compensatory stepping response required to prevent a fall. Still, individuals with stroke have unique deficits (e.g. spasticity) which draws into question if this type of training will be effective for this population. OBJECTIVE: Evaluate if a single session of trip-specific training can modify the compensatory stepping response (trunk movement, step length/duration, reaction time) of individuals with chronic stroke. METHODS: Sixteen individuals with unilateral chronic stroke participated in a single session of trip-specific training consisting of 15 treadmill perturbations. A falls assessment consisting of 3 perturbations was completed before and after training. Recovery step kinematics measured during the pre- and post-test were compared using a repeated measures design. Furthermore, Fallers (those who experienced at least one fall during the pre- or post-test) were compared to Non-fallers. RESULTS: Trip-specific training decreased trunk movement post perturbation. Specifically following training, Trunk flexion was 48 and 19 percent smaller on the small and medium perturbations at the end of the first compensatory step. Fallers (9 out of 16 subjects) post-training resembled Non-Fallers pre-training. Specifically, Trunk flexion at the completion of the first step during small and medium perturbations was not different between Fallers post-training and Non-Fallers pre-training. Still enthusiasm was tempered because Trunk flexion at the largest perturbation (where most falls occurred) was not changed and therefore total falls were not reduced as a result of this training. SIGNIFICANCE: Our results indicate that trip-specific training modifies the dynamic falls response immediately following trip-like treadmill perturbations. However, the incidence of falls was not reduced with a single training session. Further study of the implications and length of the observed intervention effect are warranted.

Ensuring accurate estimates of step width variability during treadmill walking requires more than 400 consecutive steps.

Falls to the side are associated with significant morbidity, including increased risk of hip and radius fracture. Although step width variability, as measured by standard deviation, has been hypothesized to be associated with falls to the side, there is little supporting evidence. The extent to which such a relationship could be reliably established, however, is dependent on the accuracy with which step width, and thus step width variability, is measured. It has been reported that 400 consecutive steps are required to accurately estimate step width of young adults during treadmill walking. The degree to which this requirement generalizes to other populations has not been determined. Here, a secondary analysis of step width time series data from 19 middle-age women during treadmill walking revealed that 400 steps were insufficient to accurately estimate step width or step width variability for the majority of the women sampled. Patterns observed in the data suggest the potential influence of confounding factors including acclimatization to the task and fatigue during the protocol. The results suggest that the minimum number of steps previously reported as necessary to accurately assess step width and step width variability of young adults during treadmill walking is not valid for middle-age women. Furthermore, the results point to the potential value of reproducing and/or extending the original experiment that established 400 consecutive steps as necessary to accurately estimate step kinematics among young adults.

Modifiable performance domain risk-factors associated with slip-related falls.

Falls are a major source of injury in older adults. Many falls occur after slipping. This study determined performance-related factors that both contribute to slip-related falls and that may be effectively and efficiently modified through targeted intervention. Thirty-five young adults and 21 healthy older adults (age: 70.9+/-5.1 years) were slipped in a laboratory using a slippery surface. The biomechanics of the 18 older adults who fell and the 30 younger adults who recovered following slips were analyzed. A set of potentially modifiable variables, initially based on significant between-groups differences, was further analyzed using stepwise discriminant analysis and logistic regression. The discriminant analysis correctly categorized 93.8% of the falls and recoveries based on two variables; the velocity of the slipping foot relative to the velocity of the whole body center of mass (COM), and the lateral placement of the recovery foot relative to the COM. The logistic regression determined the expected change in the odds of a recovery following a slip given a hypothesized intervention-induced improvement of these variables. Decreased velocity of the slipping foot relative to the COM, or decreased lateral placement of the recovery foot relative to the COM to zero, increased the odds of recovery by 17% and 27%, respectively. This suggests that intervention targeted at improving these specific lower extremity control variables following the onset of a slip has the potential to significantly decrease slip-related fall risk.

Trunk kinematics and fall risk of older adults: translating biomechanical results to the clinic.

This paper reviews some of our experiences over nearly 15 years of trying to determine modifiable factors that contribute to the high incidence of fall by older adults. As part of our approach, we have subjected healthy young and older adults to very large postural disturbances during locomotion, in the form of trips and slips, to which rapid compensatory responses have been necessary to avoid falling. For both trips and slips, the ability to limit trunk motion has consistently discriminated older adults who fall from both younger adults and older adults who have been able to avoid falling. We have shown that the ability to limit trunk motion can be rapidly acquired, or learned, by older adults as a result of task-specific training. The learned motor skill has demonstrated short-term retention and has been shown to effectively decrease fall-risk due to trips. Collectively, we believe the works strongly suggests that the traditional exercise-based fall-prevention and whole-body, task-specific training can synergize to reduce falls and fall-related injury in older adults.

Effects of an attention demanding task on dynamic stability during treadmill walking.

BACKGROUND: People exhibit increased difficulty balancing when they perform secondary attention-distracting tasks while walking. However, a previous study by Grabiner and Troy (J. Neuroengineering Rehabil., 2005) found that young healthy subjects performing a concurrent Stroop task while walking on a motorized treadmill exhibited decreased step width variability. However, measures of variability do not directly quantify how a system responds to perturbations. This study re-analyzed data from Grabiner and Troy 2005 to determine if performing the concurrent Stroop task directly affected the dynamic stability of walking in these same subjects. METHODS: Thirteen healthy volunteers walked on a motorized treadmill at their self-selected constant speed for 10 minutes both while performing the Stroop test and during undisturbed walking. This Stroop test consisted of projecting images of the name of one color, printed in text of a different color, onto a wall and asking subjects to verbally identify the color of the text. Three-dimensional motions of a marker attached to the base of the neck (C5/T1) were recorded. Marker velocities were calculated over 3 equal intervals of 200 sec each in each direction. Mean variability was calculated for each time series as the average standard deviation across all strides. Both "local" and "orbital" dynamic stability were quantified for each time series using previously established methods. These measures directly quantify how quickly small perturbations grow or decay, either continuously in real time (local) or discretely from one cycle to the next (orbital). Differences between Stroop and Control trials were evaluated using a 2-factor repeated measures ANOVA. RESULTS: Mean variability of trunk movements was significantly reduced during the Stroop tests compared to normal walking. Conversely, local and orbital stability results were mixed: some measures showed slight increases, while others showed slight decreases. In many cases, different subjects responded differently to the Stroop test. While some of our comparisons reached statistical significance, many did not. In general, measures of variability and dynamic stability reflected different properties of walking dynamics, consistent with previous findings. CONCLUSION: These findings demonstrate that the decreased movement variability associated with the Stroop task did not translate to greater dynamic stability.