Wearing a back-support exoskeleton alters lower-limb joint kinetics during single-step recovery following a forward loss of balance.

We assessed the effects of a passive, back-support exoskeleton (BSE) on lower-limb joint kinetics during the initiation and swing phases of recovery from a forward loss of balance. Sixteen (8M, 8F) young, healthy participants were released from static forward-leaning postures and attempted to recover their balance with a single-step while wearing a BSE (backXTM) with different levels of support torque and in a control condition. The BSE provided âˆ¼ 15-20 Nm of external hip extension torque on the stepping leg at the end of initiation and beginning of swing phases. Participants were unable to generate sufficient hip flexion torque, power, and work to counteract this external torque, although they sustained hip flexion torque for a more prolonged period, resulting in slightly increased hip contribution to positive leg work (compared to control). However, net positive leg work, and the net contribution of hip joint (human + BSE) to total leg work decreased with BSE use. While all participants had changes in hip joint kinetics, a significant compensatory increase in ankle contribution to positive leg work was observed only among females. Our results suggest that BSE use adversely affects reactive stepping by decreasing the stepping leg kinetic energy for forward propulsion, and that the relative contributions of lower-limb joints to total mechanical work done during balance recovery are altered by BSE use. BSEs may thus need to be implemented with caution for dynamic tasks in occupational settings, as they may impair balance recovery following a forward loss of balance.

Assessing the role of ankle and hip joint proprioceptive information in balance recovery using vibratory stimulation.

Background: Previous work suggests that proprioceptive information from ankle and hip are crucial in maintaining balance during upright standing; however, the contribution of these proprioceptive information during stepping balance recovery in not clear. The goal of the current study was to assess the role of ankle and hip proprioceptive information on balance recovery performance by manipulating type 1a afferent in muscle spindles using vibratory stimulation. Methods: Twenty healthy young participants were recruited (age = 22.2 ± 2.7 years) and were randomly assigned to balance recovery sessions with either ankle or hip stimulation. Trip-like perturbations were imposed using a modified treadmill setup with a protecting harness. Vibratory stimulation was imposed bilaterally on ankle and hip muscles to expose participants to three condition of no-vibration, 40Hz vibration, and 80Hz vibration. Kinematics of the trunk and lower-extremities were measured using wearable sensors to characterize balance recovery performance. Outcomes were response time, recovery step length, trunk angle during toe-off and heel-strike of recovery stepping, and required time for full recovery. Findings: Ankle vibratory stimulation elicited main effects on reaction time and recovery step length (p < 0.002); reaction time and recovery step length increased by 23.0% and 21.2%, respectively, on average across the conditions. Hip vibratory stimulation elicited significant increase in the full recovery time (p = 0.019), with 55.3% increase on average across the conditions. Interpretation: Current findings provided evidence that vibratory stimulation can affect the balance recovery performance, causing a delayed recovery initiation and an impaired balance refinement after the recovery stepping when applied to ankle and hip muscles, respectively.

Trunk postural control during unstable sitting among individuals with and without low back pain: A systematic review with an individual participant data meta-analysis.

INTRODUCTION: Sitting on an unstable surface is a common paradigm to investigate trunk postural control among individuals with low back pain (LBP), by minimizing the influence lower extremities on balance control. Outcomes of many small studies are inconsistent (e.g., some find differences between groups while others do not), potentially due to confounding factors such as age, sex, body mass index [BMI], or clinical presentations. We conducted a systematic review with an individual participant data (IPD) meta-analysis to investigate whether trunk postural control differs between those with and without LBP, and whether the difference between groups is impacted by vision and potential confounding factors. METHODS: We completed this review according to PRISMA-IPD guidelines. The literature was screened (up to 7th September 2023) from five electronic databases: MEDLINE, CINAHL, Embase, Scopus, and Web of Science Core Collection. Outcome measures were extracted that describe unstable seat movements, specifically centre of pressure or seat angle. Our main analyses included: 1) a two-stage IPD meta-analysis to assess the difference between groups and their interaction with age, sex, BMI, and vision on trunk postural control; 2) and a two-stage IPD meta-regression to determine the effects of LBP clinical features (pain intensity, disability, pain catastrophizing, and fear-avoidance beliefs) on trunk postural control. RESULTS: Forty studies (1,821 participants) were included for the descriptive analysis and 24 studies (1,050 participants) were included for the IPD analysis. IPD meta-analyses revealed three main findings: (a) trunk postural control was worse (higher root mean square displacement [RMSdispl], range, and long-term diffusion; lower mean power frequency) among individuals with than without LBP; (b) trunk postural control deteriorated more (higher RMSdispl, short- and long-term diffusion) among individuals with than without LBP when vision was removed; and (c) older age and higher BMI had greater adverse impacts on trunk postural control (higher short-term diffusion; longer time and distance coordinates of the critical point) among individuals with than without LBP. IPD meta-regressions indicated no associations between the limited LBP clinical features that could be considered and trunk postural control. CONCLUSION: Trunk postural control appears to be inferior among individuals with LBP, which was indicated by increased seat movements and some evidence of trunk stiffening. These findings are likely explained by delayed or less accurate corrective responses. SYSTEMATIC REVIEW REGISTRATION: This review has been registered in PROSPERO (registration number: CRD42021124658).

Transient use of hemolymph for hydraulic wing expansion in cicadas.

Insect wings must be flexible, light, and strong to allow dynamic behaviors such as flying, mating, and feeding. When winged insects eclose into adults, their wings unfold, actuated hydraulically by hemolymph. Flowing hemolymph in the wing is necessary for functioning and healthy wings, both as the wing forms and as an adult. Because this process recruits the circulatory system, we asked, how much hemolymph is pumped into wings, and what happens to the hemolymph afterwards? Using Brood X cicadas (Magicicada septendecim), we collected 200 cicada nymphs, observing wing transformation over 2 h. Using dissection, weighing, and imaging of wings at set time intervals, we found that within 40 min after emergence, wing pads morphed into adult wings and total wing mass increased to ~ 16% of body mass. Thus, a significant amount of hemolymph is diverted from body to wings to effectuate expansion. After full expansion, in the ~ 80 min after, the mass of the wings decreased precipitously. In fact, the final adult wing is lighter than the initial folded wing pad, a surprising result. These results demonstrate that cicadas not only pump hemolymph into the wings, they then pump it out, producing a strong yet lightweight wing.

A passive leg-support exoskeleton adversely affects reactive balance after simulated slips and trips on a treadmill.

Occupational exoskeletons have become more prevalent as an ergonomic control to reduce the physical demands of workers. While beneficial effects have been reported, there is relatively little evidence regarding potential adverse effects of exoskeletons on fall risk. The purpose of this study was to investigate the effects of a leg-support exoskeleton on reactive balance after simulated slips and trips. Six participants (three females) used a passive, leg-support exoskeleton that provided chair-like support in three experimental conditions (no exoskeleton, low-seat setting, high-seat setting). In each of these conditions, participants were exposed to 28 treadmill perturbations from an upright standing posture simulating a backward slip (0.4-1.6 m/s) or a forward trip (0.75-2.25 m/s). The exoskeleton increased the probability of a failed recovery, and adversely affected reactive balance kinematics, after simulated slips and trips. After simulated slips, the exoskeleton decreased initial step length 0.039 m, decreased mean step speed 0.12 m/s, anteriorly displaced touchdown position of the initial recovery step by 0.045 m, and decreased PSIS height at initial step touchdown by 1.7 % sof its standing height. After simulated trips, the exoskeleton increased trunk angle at step 2.4 degrees, and decreased initial step length 0.033 m. These effects appeared to result from the exoskeleton inhibiting regular stepping motion due to its posterior placement on the lower limbs, added mass, and mechanical constraints on participant movement. Our results suggest care may be needed among leg-support exoskeleton users when at risk of slips or trips and motivate potential exoskeleton design modifications to reduce fall risk.

Approximate Bayesian Techniques for Statistical Model Selection and Quantifying Model Uncertainty-Application to a Gait Study.

Frequently, biomedical researchers need to choose between multiple candidate statistical models. Several techniques exist to facilitate statistical model selection including adjusted R2, hypothesis testing and p-values, and information criteria among others. One particularly useful approach that has been slow to permeate the biomedical literature is the notion of posterior model probabilities. A major advantage of posterior model probabilities is that they quantify uncertainty in model selection by providing a direct, probabilistic comparison among competing models as to which is the "true" model that generated the observed data. Additionally, posterior model probabilities can be used to compute posterior inclusion probabilities which quantify the probability that individual predictors in a model are associated with the outcome in the context of all models considered given the observed data. Posterior model probabilities are typically derived from Bayesian statistical approaches which require specialized training to implement, but in this paper we describe an easy-to-compute version of posterior model probabilities and inclusion probabilities that rely on the readily-available Bayesian information criterion. We illustrate the utility of posterior model probabilities and inclusion probabilities by re-analyzing data from a published gait study investigating factors that predict required coefficient of friction between the shoe sole and floor while walking.

A proposed methodology for trip recovery training without a specialized treadmill.

Falls are the leading cause of accidental injuries among adults aged 65 years and older. Perturbation-based balance training is a novel exercise-based fall prevention intervention that has shown promise in reducing falls. Trip recovery training is a form of perturbation-based balance training that targets trip-induced falls. Trip recovery training typically requires the use of a specialized treadmill, the cost of which may present a barrier for use in some settings. The goal of this paper is to present a methodology for trip recovery training that does not require a specialized treadmill. A trial is planned in the near future to evaluate its effectiveness. If effective, non-treadmill trip recovery training could provide a lower cost method of perturbation-based balance training, and facilitate greater implementation outside of the research environment.

Wearing a back-support exoskeleton impairs single-step balance recovery performance following a forward loss of balance - An exploratory study.

Back-support exoskeletons (BSEs) are a promising ergonomic intervention for reducing physical demands on the low-back, but little is known regarding whether BSE use alters balance recovery following external perturbations. Hence, we investigated the effects of wearing a BSE on single-step balance recovery following a forward loss of balance. Sixteen (8 M, 8F) young, healthy participants were released from static forward-leaning postures and attempted to recover their balance with a single step while wearing a BSE (backXTM) with three different levels of support torque (i.e., no torque, low, and high) and in a control condition (no exoskeleton). Lean angle was increased until they failed in two consecutive trials to recover their balance with a single step. The maximum lean angle from which individuals could successfully recover was not significantly altered when wearing the BSE. However, wearing the BSE under all torque conditions increased reaction times. The BSE also impeded hip flexion (i.e., decrease in both peak hip flexion angle and angular velocity), resulting in decreased peak knee flexion velocity, knee range of motion, and step length. Measures of the margin of stability decreased significantly in the high-torque BSE condition. Overall, our results suggest that use of a BSE that provides external hip extension torque impairs balance recovery responses. Future work extending kinetic analyses to recovery responses, as well as a study of recovery when responding to slips and trips while walking, would offer a more complete picture of how a BSE may impact balance recovery following a loss of balance.

Fall impacts from standing show equivalence between experts in stage combat landing strategy and naïve participants after training.

BACKGROUND: Slips, trips, and falls are the second leading cause of non-fatal injuries in workplace in the United States. A stage combat landing strategy is used in the theatre arts to reduce the risk of fall-induced injury, and may be a viable approach among some working populations. OBJECTIVE: The goal of this study was to compare fall impact characteristics between experts in stage combat landing strategy and naïve participants after four training sessions of stage combat landing strategy training. METHODS: Forward and backward falls from standing were induced by releasing participants from static leans. Participants fell onto a foam mat, and impact force was measured using force platforms under the mat. A statistical equivalence test was used to determine if impact characteristics between groups were similar. RESULTS: Results indicated equivalence between groups in peak impact force during backward but not forward falls. Equivalence between groups in impact time suggested a mechanism by which equivalence in peak impact force as achieve. CONCLUSIONS: Four training sessions was sufficient for naïve participants to exhibit fall impact characteristics similar to experts in an anecdotally-effective landing strategy, and support further study. To our knowledge, this was the first study to investigate training for a landing strategy involving stepping after losses of balance from standing.

Exploring the Association Between Measures of Obesity and Measures of Trip-induced Fall Risk Among Older Adults.

OBJECTIVE: To explore the association between measures of obesity and measures of trip-induced fall risk among community-dwelling older adults. DESIGN: Case-control. SETTING: Gait laboratory. PARTICIPANTS: Voluntary sample of 55 community-dwelling older adults (aged ≥65y; N=55) with body mass index (BMI) of 18.84-44.68 kg/m2. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Measures of obesity included 6 anthropometry-based measures (BMI; thigh, hip and waist circumferences; ratio of waist-to-hip circumference; index of central obesity) and 4 dual-energy x-ray absorptiometry-based measures (percentage trunk, leg, and total fat; fat mass index). Measures of risk of tripping during overground walking included median and interquartile range of toe clearance and area under the swing phase toe trajectory. Measures of trip recovery after a laboratory-induced trip included trunk angle and angular velocity at ground contact of the first recovery step, anteroposterior distance from stepping foot to center of mass at the same instant, and step time of the first recovery step. RESULTS: Risk of tripping was associated with waist-to-hip ratio and thigh circumference. After grouping participants by waist-to-hip ratio, those with high ratios (≥0.9 cm for men and ≥0.85 cm for women) exhibited significantly greater variability in toe clearance. Trip recovery was associated with hip circumference, thigh circumference, fat mass index, and total fat. After grouping participants by fat mass index, those with high indices (>9 kg/m2 for men and >13 kg/m2 for women) exhibited less favorable trunk kinematics after a laboratory-induced trip (Cohen d=0.84). CONCLUSIONS: Waist-to-hip ratio and fat mass index may more closely relate to trip-induced fall risk than BMI among community-dwelling older adults.

RELIABILITY OF CENTER OF PRESSURE-BASED MEASURES DURING DUAL-TASK POSTURAL CONTROL TESTING IN A YOUTH POPULATION.

BACKGROUND: Dual-task assessments can identify changes in postural control during recovery from a concussion. However, developing postural control in children presents a challenge when using adult balance assessments to examine children. PURPOSE: The purpose of this study was to investigate the reliability of a cognitive dual-task postural control testing protocol among a youth sample with no history of concussion or exposure to head impacts. STUDY DESIGN: Reliability pilot study. METHODS: Testing comprised nine 120 second trials of standing on a force plate collecting data at 250 Hz. Test conditions included no dual-task, counting backwards by 2, counting backwards by 3, listening, and the Stroop test. Subjects completed each test with open and closed eyes, except for the Stroop test. The force plate was used to measure the subjects' center of pressure (COP) trajectory. RESULTS: Nine healthy, youth subjects (average age: 11.6 ± 0.5 years) with no history of concussion or exposure to head impacts participated. Reliability was good (>0.6) or excellent (>0.75) for COP speed, sway, and sample entropy measures for several test conditions. The eyes open, no task condition produced the lowest COP measures. No differences were observed between the other dual-task conditions. CONCLUSION: Given its high measures of reliability, this dual-task protocol might be able to detect postural control changes in concussed youth athletes. EVIDENCE LEVEL: 2.

Improvement in trunk kinematics after treadmill-based reactive balance training among older adults is strongly associated with trunk kinematics before training.

Reactive balance training (RBT) is an emerging fall prevention exercise intervention for older adults. To better understand factors that influence improvements after RBT, the goal of this study was to identify key factors that strongly associate with training-induced improvements in reactive balance. This study is a secondary analysis of data from a prior study. Twenty-eight residents of senior housing facilities participated, including 14 RBT participants and 14 Tai Chi participants (controls). Before and one week after training, participants completed balance and mobility tests and a reactive balance test. Reactive balance was operationalized as the maximum trunk angle in response to standardized trip-like perturbations on a treadmill. Bivariate (Pearson) correlation was used to identify participant characteristics before RBT and measures of performance during RBT that associated with training-induced changes in maximum trunk angle. Maximum trunk angle before reactive balance training exhibited the strongest association with training-induced changes in maximum trunk angle among RBT participants (r2 = 0.84; p < .001), but not among Tai Chi participants (r2 = 0.17; p = .138). Measures of performance during RBT, based upon perturbation speed, also associated with RBT-induced improvements in maximum trunk angle. These results help clarify the characteristics of individuals who can benefit from RBT, and support the use of treadmill perturbation speed as a surrogate measure of training-induced improvements in trunk kinematics.

Effects of Manual Material Handling Workload on Measures of Fall Risk.

OCCUPATIONAL APPLICATIONS We found, contrary to expectations, that performing a fatiguing simulated heavy manual material handling (MMH) task did not adversely affect the risk of trip-induced falls when compared to a less-fatiguing light MMH task. However, when considering these MMH tasks together rather than in comparison, our results provide evidence for adverse effects of fatigue on both gait and the ability to recover balance after tripping. The current results provide additional evidence that physical fatigue increases fall risk, start to clarify the mechanisms by which this increase occurs, and can help in developing and evaluating fall prevention strategies targeting these mechanisms.

TECHNICAL ABSTRACT Background Falls are a leading cause of occupational injuries, and the incidence of occupational falls may be exacerbated by physical fatigue resulting from physically-demanding work. Purpose: The goal of this study was to evaluate the effects of occupationally-relevant physical fatigue on the risk of trip-induced falls. Methods: Thirty-six healthy young adults performed two-hours of a simulated heavy manual material handling (MMH) task (experimental group) or a light MMH task (control group). Risks of tripping and slipping were evaluated before and after completing the task, and one laboratory-induced trip while walking was induced after completing the MMH task. Results: Compared to the light MMH task, the heavy MMH task did not adversely affect the risk of tripping or slipping during gait, reactive balance after tripping, or fall rate after tripping. These results may have been due to an insufficient difference in fatigue level between groups. When both groups were considered together, however, the MMH tasks resulted in an unsteady gait, an increased risk of slipping while walking and carrying a load, and a fall rate that was substantially higher than reported in other studies. Conclusions: Although the effects of the heavy and light MMH tasks did not differ, changes in fall risk measures when considering both MMH tasks as one provide evidence for the biomechanical mechanisms by which physical fatigue may increase the risk of occupational falls.

Perturbation-based balance training targeting both slip- and trip-induced falls among older adults: a randomized controlled trial.

BACKGROUND: Falls are the leading cause of injuries among older adults. Perturbation-based balance training (PBT) is an innovative approach to fall prevention that aims to improve the reactive balance response following perturbations such as slipping and tripping. Many of these PBT studies have targeted reactive balance after slipping or tripping, despite both contributing to a large proportion of older adult falls. The goal of this randomized controlled trial was to evaluate the effects of PBT targeting slipping and tripping on laboratory-induced slips and trips. To build upon prior work, the present study included: 1) a control group; 2) separate training and assessment sessions; 3) PBT methods potentially more amenable for use outside the lab compared to methods employed elsewhere, and 4) individualized training for older adult participants. METHODS: Thirty-four community-dwelling, healthy older adults (61-75 years) were assigned to PBT or a control intervention using minimization. Using a parallel design, reactive balance (primary outcome) and fall incidence were assessed before and after four sessions of BRT or a control intervention involving general balance exercises. Assessments involved exposing participants to an unexpected laboratory-induced slip or trip. Reactive balance and fall incidence were compared between three mutually-exclusive groups: 1) baseline participants who experienced a slip (or trip) before either intervention, 2) post-control participants who experienced a slip (or trip) after the control intervention, and 3) post-PBT participants who experienced a slip (or trip) after PBT. Neither the participants nor investigators were blinded to group assignment. RESULTS: All 34 participants completed all four sessions of their assigned intervention, and all 34 participants were analyzed. Regarding slips, several measures of reactive balance were improved among post-PBT participants when compared to baseline participants or post-control participants, and fall incidence among post-PBT participants (18%) was lower than among baseline participants (80%). Regarding trips, neither reactive balance nor fall incidence differed between groups. CONCLUSIONS: PBT targeting slipping and tripping improved reactive balance and fall incidence after laboratory-induced slips. Improvements were not observed after laboratory-induced trips. The disparity in efficacy between slips and trip may have resulted from differences in dosage and specificity between slip and trip training. TRIAL REGISTRATION: Name of Clinical Trial Registry: clinicaltrials.gov Trial Registration number: NCT04308239. Date of Registration: March 13, 2020 (retrospectively registered).

Risk Factors for Postural and Functional Balance Impairment in Patients with Chronic Obstructive Pulmonary Disease.

Reduced balance function has been observed during balance challenging conditions in the chronic obstructive pulmonary disease (COPD) population and is associated with an increased risk of falls. This study aimed to examine postural balance during quiet standing with eyes open and functional balance in a heterogeneous group of COPD and non-COPD (control) subjects, and to identify risk factors underlying balance impairment using a large panel of methods. In COPD and control subjects, who were mostly overweight and sedentary, postural and functional balance were assessed using center-of-pressure displacement in anterior-posterior (AP) and medio-lateral (ML) directions, and the Berg Balance Scale (BBS), respectively. COPD showed 23% greater AP sway velocity (p = 0.049). The presence of oxygen therapy, fat mass, reduced neurocognitive function, and the presence of (pre)diabetes explained 71% of the variation in postural balance in COPD. Transcutaneous oxygen saturation, a history of exacerbation, and gait speed explained 83% of the variation in functional balance in COPD. Neurocognitive dysfunction was the main risk factor for postural balance impairment in the control group. This suggests that specific phenotypes of COPD patients can be identified based on their type of balance impairment.

Potential Implementation of Reactive Balance Training within Continuing Care Retirement Communities.

PURPOSE: The purpose of the study was to evaluate the feasibility of implementing reactive balance training (RBT) in continuing care retirement communities, as a part of typical practice in these facilities. METHODS: RBT, a task-specific exercise program, consisted of repeatedly exposing participants to trip-like perturbations on a modified treadmill to improve reactive balance, and subsequently reduce fall risk. Semi-structured interviews were conducted with retirement community residents (RBT participants) and administrators, to assess the organizational context, perceptions of evidence for falls prevention, and facilitation strategies that could improve the likelihood of implementing RBT as a falls-prevention program. RESULTS: Contextual factors such as leadership support, culture of change, evaluation capabilities, and receptivity to RBT among administrators and health leaders at the participating retirement communities could facilitate future implementation. The cost associated with RBT (e.g. equipment and personnel), resident recruitment, and accessibility of RBT for many residents were identified as primary barriers related to the intervention. Participants perceived observable health benefits after completing RBT, had increased awareness toward tripping, and greater confidence with respect to mobility. Across interviewees potential barriers for implementation regarding facilitation revolved around the compatibility and customizability for different participant capabilities that would need to be considered before adopting RBT. CONCLUSION: RBT could fill a need in retirement communities and the findings provide areas of context, characteristics of the intervention, and facilitation approaches that could improve uptake.

Relative Effort while Walking Is Higher among Women Who Are Obese, and Older Women.

PURPOSE: Individuals who are obese, and older individuals, exhibit gait alterations that may result, in part, from walking with greater effort relative to their maximum strength capacity. The goal of this study was to investigate obesity-related and age-related differences in relative effort during gait. METHODS: Four groups of women completed the study, including 10 younger healthy-weight, 10 younger obese, 10 older healthy-weight, and 9 older obese women. The protocol included strength measurements at the hip, knee, and ankle in both flexion and extension, and gait trials under self-selected and constrained (1.5 m·s gait speed and 0.65-m step length) conditions. Relative effort was calculated as the ratio of joint torques during gait, and strength from a subject-specific model that predicted strength as a function of joint angle. RESULTS: Relative effort during self-selected gait was higher among women who were obese in knee extension (P = 0.028) and ankle plantar flexion (P = 0.013). Although both joint torques and strength were higher among women who were obese, these increases in relative effort were attributed to greater obesity-related increases in joint torques than strength. Relative effort was also higher among older women in hip flexion (P < 0.001) and knee extension (P = 0.008), and attributed to age-related strength loss. Results were generally similar between self-selected and constrained gait, indicating the greater relative effort among women who were obese and older women was not attributed to differences in gait spatiotemporal characteristics. CONCLUSIONS: Women who were obese, as well as older women, walk with greater relative effort. These results may help explain the compromised walking ability among these individuals.

Comparison of Treadmill Trip-Like Training Versus Tai Chi to Improve Reactive Balance Among Independent Older Adult Residents of Senior Housing: A Pilot Controlled Trial.

BACKGROUND: There is growing interest in using perturbation-based balance training to improve the reactive response to common perturbations (eg, tripping and slipping). The goal of this study was to compare the efficacy of treadmill-based reactive balance training versus Tai Chi performed at, and among independent residents of, older adult senior housing. METHODS: Thirty-five residents from five senior housing facilities were allocated to either treadmill-based reactive balance training or Tai Chi training. Both interventions were performed three times per week for 4 weeks, with each session lasting approximately 30 minutes. A battery of balance tests was performed at baseline, and again 1 week, 1 month, 3 months, and 6 months post-training. The battery included six standard clinical tests of balance and mobility, and a test of reactive balance performance. RESULTS: At baseline, no significant between-group differences were found for any balance tests. After training, reactive balance training participants had better reactive balance than Tai Chi participants. Maximum trunk angle was 13.5° smaller among reactive balance training participants 1 week after training (p = .01), and a reactive balance rating was 24%-31% higher among reactive balance training participants 1 week to 6 months after training (p < .03). Clinical tests showed minimal differences between groups at any time point after training. CONCLUSION: Trip-like reactive balance training performed at senior housing facilities resulted in better rapid balance responses compared with Tai Chi training.

Age-related strength loss affects non-stepping balance recovery.

Aging is associated with a higher risk of falls, and an impaired ability to recover balance after a postural perturbation is an important contributing factor. In turn, this impaired recovery ability likely stems from age-related decrements in lower limb strength. The purpose of this study was to investigate the effects of age-related strength loss on non-stepping balance recovery capability after a perturbation while standing, without constraining movements to the ankle as in prior reports. Two experiments were conducted. In the first, five young adults (ages 20-30) and six community-dwelling older adults (ages 70-80) recovered their balance, without stepping, from a backward displacement of a support surface. Balance recovery capability was quantified as the maximal backward platform displacement that a subject could withstand without stepping. The maximal platform displacement was 27% smaller among the older group (11.8±2.1 cm) vs. the young group (16.2±2.6 cm). In the second experiment, forward dynamic simulations of a two-segment, rigid-body model were used to investigate the effects of manipulating strength in the hip extensors/flexors and ankle plantar flexors/dorsiflexors. In these, typical age-related reductions in strength were included. The model predicted lower maximal platform displacements with age-related reductions only in plantar flexion and hip flexion strength. These findings support the previously reported age-related loss of balance recovery ability, and an important role for plantar flexor strength in this ability.