Erosion of Stumble Correction Evoked with Superficial Peroneal Nerve Stimulation in Older Adults during Walking.

In healthy young adults, electrical stimulation of the superficial peroneal cutaneous nerve (SPn) innervating the dorsum of the foot has been shown to elicit functionally relevant reflexes during walking that are similar to those evoked by mechanical perturbation to the dorsum of the foot during walking and are referred to as stumble corrective (obstacle avoidance) responses. Though age-related differences in reflexes induced by mechanical perturbation have been studied, toe clearance has not been measured. Further, age-related differences in reflexes evoked by electrical stimulation of SPn have yet to be determined. Thus, the purpose of this study was to characterize age-related differences between healthy young adults and older adults with no history of falls in stumble correction responses evoked by electrical stimulation of the SPn at the ankle during walking. Toe clearance relative to the walking surface along with joint displacement and angular velocity at the ankle and knee and EMG of the tibialis anterior, medial gastrocnemius, biceps femoris and vastus lateralis were measured. The combined background and reflex toe clearance was reduced in the older adults compared with the young in mid-early swing (p = 0.011). These age-related differences likely increase fall risk in the older adult cohort. Further, age-related changes were seen in joint kinematics and EMG in older adults compared with the young such as decreased amplitude of the plantarflexion reflex in early swing in older adults (p < 0.05). These altered reflexes reflect the degradation of the stumble corrective response in older adults.

Can minimum toe clearance predict community-based trips by older adults?

BACKGROUND: Tripping is the leading cause of falls by older adults. While tripping theoretically occurs when minimum toe clearance (MTC) is insufficient to avoid an unseen obstacle, the relationship between MTC and community-based trips is unknown. RESEARCH QUESTION: To what extent do MTC and its variability predict the number of community-based trips during gait by older adults? METHOD: 51 older adults with normal or obese body mass index walked across an 8 m walkway. For each step, we identified MTC as the local minimum of the vertical trajectory of a toe marker during the swing phase. We calculated the across-steps mean, median, interquartile range, and standard deviation for MTC, and skewness and kurtosis of the distribution of all MTC values for an individual. Every two weeks for one year, participants reported on community-based trips. A series of negative binomial regressions were used to predict the number of trips over obstacles (with or without a fall) based on MTC measures. RESULTS: 28 participants experienced at least one trip, with 14 experiencing two or more. In the absence of any covariates, only kurtosis and skewness significantly predicted the incidence rate of trips. However, neither remained significant after accounting for fall history. The model that included kurtosis and fall history predicted trips better than one with fall history alone, with the incidence rate of trips decreasing by 35% for every unit increase in kurtosis (incidence rate ratio of 0.64 with 95% confidence interval: 0.38 - 1.08; p = 0.09) SIGNIFICANCE: While MTC has the potential to provide insight into older adults more likely to trip over obstacles in the community, assessing MTC during level-ground walking within a lab environment may lack ecological validity to strongly describe the risk of community-based trips above and beyond fall history.

Efficacy of stumble recovery assistance in a knee exoskeleton for individuals with simulated mobility impairment: A pilot study.

Falls due to stumbles are a major cause of injury for many populations, and as such interventions to reduce fall risk have been a key focus of rehabilitation research. However, dedicated stumble recovery assistance in a powered lower-limb exoskeleton has yet to be explored as a fall mitigation intervention. Thus young, healthy adults () were recruited for a stumble recovery experiment to test the efficacy of knee exoskeleton stumble recovery assistance in improving an impaired stumble recovery response (i.e., the elevating strategy response). Leg weights were attached unilaterally to each participant's shank to simulate walking and stumble recovery impairment, and a unilateral powered knee exoskeleton was worn on the same leg for walking and stumble recovery assistance. Ultimately, knee exoskeleton stumble recovery assistance served to improve participants' elevating limb kinematics (i.e., increase thigh and knee motion) and reduce overall fall risk (i.e., reduce trunk motion and improve foot placement) during responses relative to their impaired response (i.e., with the leg weights and no assistance), and relative to their response while receiving only walking assistance. This initial exploration provides a first indication that knee exoskeleton stumble recovery assistance is a viable approach to improving an impaired stumble recovery response, which could serve two important use cases: (1) a safety mechanism for existing exoskeleton wearers, who may be less capable of recovering from stumbles due to the added weight or joint impedance of the device; (2) an external stumble recovery aid for fall-prone populations, such as the elderly or stroke survivors.

Factors leading to falls in transfemoral prosthesis users: a case series of sound-side stumble recovery responses.

BACKGROUND: Transfemoral prosthesis users' high fall rate is related to increased injury risk, medical costs, and fear of falling. Better understanding how stumble conditions (e.g., participant age, prosthesis type, side tripped, and swing phase of perturbation) affect transfemoral prosthesis users could provide insight into response deficiencies and inform fall prevention interventions. METHODS: Six unilateral transfemoral prosthesis users experienced obstacle perturbations to their sound limb in early, mid, and late swing phase. Fall outcome, recovery strategy, and kinematics of each response were recorded to characterize (1) recoveries versus falls for transfemoral prosthesis users and (2) prosthesis user recoveries versus healthy adult recoveries. RESULTS: Out of 26 stumbles, 15 resulted in falls with five of six transfemoral prosthesis users falling at least once. By contrast, in a previously published study of seven healthy adults comprising 214 stumbles using the same experimental apparatus, no participants fell. The two oldest prosthesis users fell after every stumble, stumbles in mid swing resulted in the most falls, and prosthesis type was not related to strategy/fall outcomes. Prosthesis users who recovered used the elevating strategy in early swing, lowering strategy in late swing, and elevating or lowering/delayed lowering with hopping in mid swing, but exhibited increased contralateral (prosthetic-side) thigh abduction and trunk flexion relative to healthy controls. Falls occurred if the tripped (sound) limb did not reach ample thigh/knee flexion to sufficiently clear the obstacle in the elevating step, or if the prosthetic limb did not facilitate a successful step response after the initial sound-side elevating or lowering step. Such responses generally led to smaller step lengths, less anterior foot positioning, and more forward trunk flexion/flexion velocity in the resulting foot-strikes. CONCLUSIONS: Introducing training (e.g., muscle strength or task-specific motor skill) and/or modifying assistive devices (e.g., lower-limb prostheses or exoskeletons) may improve responses for transfemoral prosthesis users. Specifically, training or exoskeleton assistance could help facilitate sufficient thigh/knee flexion for elevating; training or prosthesis assistance could provide support-limb counteracting torques to aid in elevating; and training or prosthesis assistance could help initiate and safely complete prosthetic swing.

A novel system for introducing precisely-controlled, unanticipated gait perturbations for the study of stumble recovery.

BACKGROUND: The experimental study of stumble recovery is essential to better understanding the reflexive mechanisms that help prevent falls as well as the deficiencies in fall-prone populations. This study would benefit from a system that can introduce perturbations that: 1) are realistic (e.g., obstacle disrupting the foot in swing phase), 2) are unanticipated by subjects, 3) are controllable in their timing, and 4) allow for kinematic and kinetic evaluation. METHODS: A stumble perturbation system was designed that consists of an obstacle delivery apparatus that releases an obstacle onto a force-instrumented treadmill and a predictive targeting algorithm which controls the timing of the perturbation to the foot during swing phase. Seven healthy subjects were recruited to take part in an experimental protocol for system validation, which consisted of two sub-experiments. First, a perception experiment determined whether subjects could perceive the obstacle as it slid onto the treadmill belt. Second, a perturbation experiment assessed the timing accuracy of perturbations relative to a target percent swing input by the experimenter. Data from this experiment were then used to demonstrate that joint kinematics and kinetics could be computed before and after the perturbation. RESULTS: Out of 168 perception trials (24 per subject), not a single obstacle was perceived entering the treadmill by the subjects. Out of 196 perturbation trials, 190 trials successfully induced a stumble event, with a mean targeting accuracy, relative to the desired percent swing, of 25 ms (6.2% of swing phase). Joint kinematic and kinetic results were then computed for three common stumble recovery strategies and shown to be qualitatively consistent with results from prior stumble studies conducted overground. CONCLUSIONS: The stumble perturbation system successfully introduced realistic obstacle perturbations that were unanticipated by subjects. The targeting accuracy substantially reduced mistrials (i.e., trials that did not elicit a stumble) compared to previous studies. This accuracy enables stumble recovery to be studied more systematically as a function of when the perturbation occurs during swing phase. Lastly, joint kinematic and kinetic estimates allow for a comprehensive analysis of stumble recovery biomechanics.

Should we consider steps with variable height for a safer stair negotiation in older adults?

BACKGROUND: Effects of exercise on foot clearances are important. In older adults variations in foot clearances during walking may lead to a fall, but there is a lack of information concerning stair negotiation in older adults. Whether a condition of post exercise changes foot clearances between steps of a staircase in older adults still unknown. OBJECTIVE: To determine differences in clearances when older adults negotiate different steps of a staircase before and after a session of aerobic exercise. METHODS: Kinematics data from 30 older adults were acquired and the toe and heel clearances were determined for each step. Clearances were compared between the steps. RESULTS: Smaller clearances were found at the highest step during ascending and descending, which was not changed by exercise. Smaller clearances suggest higher risk of tripping at the top of the staircase, regardless of exercise. CONCLUSION: A smaller step at the top of a short flight of stairs could reduce chances of tripping in older adults. It suggests that steps with variable height could make stair negotiation safer in older adults. This hypothesis should be tested in further studies.

Variability and reliability of gait kinematic parameters after controlled tripping in older adults: a preliminary study / Variabilidade e confiabilidade dos parâmetros cinemáticos da marcha de idosos após um tropeço controlado: estudo preliminar

ABSTRACT Approximately 21% of the falls in older adults occur due to tripping, while walking. There is a paucity of information regarding the gait variability and reliability when a tripping is induced in different days mainly with elderly. It was aimed to analyze the variability and the reliability (intra- and inter-day) of spatiotemporal gait parameters and joint angles after controlled tripping in older adults. Eight healthy older women participated. The trip was induced during the early-mid swing phase on the transposing segment and the kinematic data was obtained from trials. The variability and reliability of spatiotemporal gait parameters and joint angles during the gait cycle were checked through the coefficient of variation (CV), the intraclass coefficient correlation (ICC) and the standard error of measurement (SEM). The variability of spatiotemporal and intra- and inter-day angular parameters was low for most variables, except for plantar flexion. The SEM was low for all parameters. Intra-day reliability was moderate to high for the spatiotemporal and angular parameters. Inter-day reliability was considered low to moderate for all parameters. The variables did not differ between instants and days. Experimental procedures demonstrate that the walking pattern did not change, but should be considered with caution in studies that include intervention, particularly for angular parameters during gait.

RESUMO Aproximadamente 21% das quedas em idosos ocorrem como consequência de tropeços ao caminhar. Há uma escassez de informações referentes à variabilidade e à confiabilidade dos parâmetros cinemáticos da marcha em diferentes dias de avaliação, sobretudo com idosos. Buscou-se analisar a variabilidade e a confiabilidade (intra e inter-dia) dos parâmetros espaço-temporais e angulares da marcha de idosos, após a indução de tropeço controlado. Oito idosas participaram do estudo. O tropeço foi induzido durante o início da fase de balanço da marcha. Foram analisados os dados cinemáticos das tentativas de marcha. A variabilidade e confiabilidade dos parâmetros espaço-temporais da marcha foram verificados através do coeficiente de variação (CV), do coeficiente de correlação intraclasse (ICC) e do erro padrão de medida (SEM). A variabilidade dos parâmetros espaço-temporais e angulares intra e inter-dia foi baixa para a maioria das variáveis, à exceção da flexão plantar. O SEM foi baixo para todos os parâmetros. A confiabilidade intra-dia foi moderada a alta para os parâmetros espaço-temporais e angulares; A confiabilidade inter-dia foi baixa a moderada para todos os parâmetros. As variáveis não diferiram entre instantes e dias. Apesar do padrão de marcha não ter alterado deve ser analisado com cautela em estudos que incluam intervenção, particularmente para os parâmetros angulares.

Phase resetting behavior in human gait is influenced by treadmill walking speed.

Gait is often modeled as a limit cycle oscillator. When perturbed, this type of system will reset its output in a stereotypical manner, which may be shifted in time with respect to its original trajectory. In contrast to other biological oscillators, relatively little is known regarding the phase resetting properties for human gait. Because humans must often reset their gait in response to perturbation, an improved understanding of this behavior may have implications for reducing the risk of fall. The purpose of this study was to further evaluate phase resetting behaviors in human gait with particular emphasis on (1) variance of the phase resetting response among healthy individuals and (2) the sensitivity of this response to walking speed. Seventeen healthy subjects walked on a treadmill at 2.0mph, 2.5mph, and 3.0mph while their right limb was perturbed randomly every 12-20 strides. Discrete, mechanical perturbations were applied by a rope that was attached to each subject's ankle and actuated by a motorized arm. Perturbations were applied once during a select stride, always at a different point in the swing phase, and the amount of phase shift that occurred on the subsequent stride was recorded. A subset of 8 subjects also walked at their preferred walking speed for 3 additional trials on a separate day in order to provide an estimate of within-subjects variability. The results suggested that phase resetting behavior is relatively consistent among subjects, but that minor variations in phase resetting behavior are attributable to walking at different treadmill speeds.

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.