Can treadmill-slip perturbation training reduce immediate risk of over-ground-slip induced fall among community-dwelling older adults?

Combined musculoskeletal finite element modeling of femur stress during reactive balance training

The purpose of this study was to determine the material stresses experienced in the femoral neck during the stepping phase of recovery from a forward loss of balance achieved both using release from a static forward lean and rapid treadmill accelerations in 8 older adults. A scalable musculoskeletal model with 23 degrees of freedom and 92 force actuators was used to calculate joint reaction forces. A finite element model of the femur used joint reaction forces calculated by the musculoskeletal model to calculate the material stresses during stepping. Balance recovery from a static forward lean angle had a greater joint contact force and greater maximum tensile stress than a recovery from treadmill induced perturbations both before and after a training session. Hip joint contact loads were found to be large in magnitude, however, all stresses experienced by the bone are less than critical yield stresses for trabecular bone. We suggest that stepping balance recovery is safe for older adults with no obvious loss of bone density or strength and that analyses such as finite element analysis are necessary to understand stresses in the material at the joint level.

Functional electrical stimulation to enhance reactive balance among people with hemiparetic stroke

BACKGROUND

Individuals with stroke demonstrate a twofold higher fall incidence compared to healthy counterparts, potentially associated with deficits in reactive balance control, which is crucial for regaining balance from unpredictable perturbations to the body. Moreover, people with higher stroke-related motor impairment exhibit greater falls and cannot recover balance during higher perturbation intensities. Thus, they might need supplemental agents for fall prevention or even to be included in a perturbation-based protocol. Functional electrical stimulation is a widely used clinical modality for improving gait performance; however, it remains unknown whether it can enhance or interfere with reactive balance control.

METHODS

We recruited twelve ambulatory participants with hemiparetic stroke (61.48 ± 6.77 years) and moderate-to-high motor impairment (Chedoke-McMaster Stroke Leg Assessment ≤ 4/7). Each participant experienced 4 unpredicted paretic gait-slips, with and without functional electrical stimulation (provided 50-500 ms after perturbation) in random order. The paretic quadriceps muscle group was chosen to receive electrical stimulation, considering the role of support limb knee extensors for preventing limb-collapse. Outcomes including primary (laboratory falls), secondary (reactive stability, vertical limb support) and tertiary (compensatory step length, step initiation, execution time) measures were compared between the two conditions.

RESULTS

Participants demonstrated fewer falls, higher reactive stability, and higher vertical limb support (p < 0.05) following gait-slips with functional electrical stimulation compared to those without. This was accompanied by reduced step initiation time and a longer compensatory step (p < 0.05).

CONCLUSION

The application of functional electrical stimulation to paretic quadriceps following gait-slips reduced laboratory fall incidence with enhanced reactive balance outcomes among people with higher stroke-related motor impairment. Our results lay the preliminary groundwork for understanding the instantaneous neuromodulatory effect of functional electrical stimulation in preventing gait-slip falls, future studies could test its therapeutic effect on reactive balance. Clinical registry number: NCT04957355.

Effects of Perturbation-Based Treadmill Training on Balance Performance, Daily Life Gait, and Falls in Older Adults: REACT Randomized Controlled Trial

OBJECTIVE

The aim of this study was to evaluate the effect of perturbation-based treadmill training on gait quality in daily life, a predictor of fall risk that was used as the primary outcome. An additional aim was to evaluate the effects on secondary outcomes, including balance, gait performance, self-efficacy, daily life physical activity, and falls.

METHODS

Seventy community-dwelling older adults (mean age = 74.73 [SD = 5.69] years; 46 women) at risk of falling were randomized and received 4 weeks of dual-task treadmill training, either with or without treadmill perturbations. Balance, gait performance, self-efficacy, and daily life trunk accelerometry at baseline, after intervention, and at a 6-month follow-up were assessed and compared within group over time and between groups for each time point, and their change rates between groups over time were also assessed.

RESULTS

Both groups improved in their balance, gait performance, and self-efficacy; the experimental group showed a significantly larger decrease in concern of falling and an increase in physical performance than the controls. These training effects did not translate into significant improvements in daily life gait quality or physical activity. However, the number of daily life falls and the percentage of fallers decreased significantly more in the experimental group.

CONCLUSION

A 4-week perturbation-based dual-task treadmill training program can improve self-efficacy, balance, and gait performance in a controlled setting and reduce daily life falls, although not through changes in quantity or quality of daily life gait.

IMPACT

Perturbation-based treadmill training is a safe and efficient way to train older adults' balance recovery and gait performance, increase self-efficacy, and prevent falls.

A neuromusculoskeletal modelling approach to bilateral hip mechanics due to unexpected lateral perturbations during overground walking

BACKGROUND

Current studies on how external perturbations impact gait dynamics have primarily focused on the changes in the body's center of mass (CoM) during treadmill walking. The biomechanical responses, in particular to the multi-planar hip joint coordination, following perturbations in overground walking conditions are not completely known.

METHODS

In this study, a customized gait-perturbing device was designed to impose controlled lateral forces onto the subject's pelvis during overground walking. The biomechanical responses of bilateral hips were simulated by subject-specific neuromusculoskeletal models (NMS) driven by in-vivo motion data, which were further evaluated by statistical parameter mapping (SPM) and muscle coactivation index (CI) analysis. The validity of the subject-specific NMS was confirmed through comparison with measured surface electromyographic signals.

RESULTS

Following perturbations, the sagittal-plane hip motions were reduced for the leading leg by 18.39° and for the trailing leg by 8.23°, while motions in the frontal and transverse plane were increased, with increased hip abduction for the leading leg by 10.71° and external rotation by 9.06°, respectively. For the hip kinetics, both the bilateral hip joints showed increased abductor moments during midstance (20%-30% gait cycle) and decreased values during terminal stance (38%-48%). Muscle CI in both sagittal and frontal planes was significantly decreased for perturbed walking (p < 0.05), except for the leading leg in the sagittal plane.

CONCLUSION

The distinctive phase-dependent biomechanical response of the hip demonstrated its coordinated control strategy for balance recovery due to gait perturbations. And the changes in muscle CI suggested a potential mechanism for rapid and precise control of foot placement through modulation of joint stiffness properties. These findings obtained during actual overground perturbation conditions could have implications for the improved design of wearable robotic devices for balance assistance.

Fall prevention by reactive balance training on a perturbation treadmill: is it feasible for prefrail and frail geriatric patients? A pilot study

PURPOSE

Prefrail and frail geriatric patients are at high risk of falling. Perturbation-based balance training on a treadmill appears to be highly effective, but there are no studies in prefrail and frail geriatric hospital patients. The aim of the work is to characterize the study population in whom reactive balance training on a perturbation treadmill was feasible.

METHODS

The study is recruiting patients with at least one fall event in the past year (age ≥ 70). The patients complete a minimum of 60-min treadmill training with/without perturbations on at least 4 occasions.

RESULTS

Until now, 80 patients (mean age 80 ± 5) took part in the study. More than half of the participants had some cognitive impairment with < 24 pts. (median MoCA 21 pts.), 35% were prefrail and 61% were frail. The drop-out rate was initially 31% and was reduced to 12% after adding a short pre-test on the treadmill.

CONCLUSION

Reactive balance training on a perturbation treadmill is feasible for prefrail and frail geriatric patients. Its effectiveness in fall prevention in this population needs to be proven.

TRIAL REGISTRATION

German Clinical trial register (DRKS-ID: DRKS00024637 on 24.02.2021).

The effect of perturbation-based balance training on balance control and fear of falling in older adults: a single-blind randomised controlled trial

BACKGROUND

Perturbation-based balance training (PBT) is an emerging intervention shown to improve balance recovery responses and reduce falls in everyday life in older adults. However, perturbation interventions were heterogeneous in nature and need improvement. This study aims to investigate the effects of a PBT protocol that was designed to address previously identified challenges of PBT, in addition to usual care, on balance control and fear of falling in older adults at increased risk of falling.

METHODS

Community-dwelling older adults (age ≥ 65 years) who visited the hospital outpatient clinic due to a fall incident were included. Participants received PBT in addition to usual care (referral to a physiotherapist) versus usual care alone. PBT consisted of three 30-minute sessions in three weeks. Unilateral treadmill belt accelerations and decelerations and platform perturbations (shifts and tilts) were applied during standing and walking on the Computer Assisted Rehabilitation Environment (CAREN, Motek Medical BV). This dual-belt treadmill embedded in a motion platform with 6 degrees of freedom is surrounded by a 180° screen on which virtual reality environments are projected. Duration and contents of the training were standardised, while training progression was individualised. Fear of falling (FES-I) and balance control (Mini-BESTest) were assessed at baseline and one week post-intervention. Primary analysis compared changes in outcome measures between groups using Mann-Whitney U tests.

RESULTS

Eighty-two participants were included (PBT group n = 39), with a median age of 73 years (IQR 8 years). Median Mini-BESTest scores did not clinically relevantly improve and were not significantly different between groups post-intervention (p = 0.87). FES-I scores did not change in either group.

CONCLUSIONS

Participation in a PBT program including multiple perturbation types and directions did not lead to different effects than usual care on clinical measures of balance control or fear of falling in community-dwelling older adults with a recent history of falls. More research is needed to explore how to modulate PBT training dose, and which clinical outcomes are most suitable to measure training effects on balance control.

TRIAL REGISTRATION

Nederlands Trial Register NL7680. Registered 17-04-2019 - retrospectively registered. https://www.trialregister.nl/trial/7680 .

Provoking Artificial Slips and Trips towards Perturbation-Based Balance Training: A Narrative Review

Humans' balance recovery responses to gait perturbations are negatively impacted with ageing. Slip and trip events, the main causes preceding falls during walking, are likely to produce severe injuries in older adults. While traditional exercise-based interventions produce inconsistent results in reducing patients' fall rates, perturbation-based balance training (PBT) emerges as a promising task-specific solution towards fall prevention. PBT improves patients' reactive stability and fall-resisting skills through the delivery of unexpected balance perturbations. The adopted perturbation conditions play an important role towards PBT's effectiveness and the acquisition of meaningful sensor data for studying human biomechanical reactions to loss of balance (LOB) events. Hence, this narrative review aims to survey the different methods employed in the scientific literature to provoke artificial slips and trips in healthy adults during treadmill and overground walking. For each type of perturbation, a comprehensive analysis was conducted to identify trends regarding the most adopted perturbation methods, gait phase perturbed, gait speed, perturbed leg, and sensor systems used for data collection. The reliable application of artificial perturbations to mimic real-life LOB events may reduce the gap between laboratory and real-life falls and potentially lead to fall-rate reduction among the elderly community.

Perturbation-based balance training: Principles, mechanisms and implementation in clinical practice

Since the mid-2000s, perturbation-based balance training has been gaining interest as an efficient and effective way to prevent falls in older adults. It has been suggested that this task-specific training approach may present a paradigm shift in fall prevention. In this review, we discuss key concepts and common issues and questions regarding perturbation-based balance training. In doing so, we aim to provide a comprehensive synthesis of the current evidence on the mechanisms, feasibility and efficacy of perturbation-based balance training for researchers and practitioners. We address this in two sections: "Principles and Mechanisms" and "Implementation in Practice." In the first section, definitions, task-specificity, adaptation and retention mechanisms and the dose-response relationship are discussed. In the second section, issues related to safety, anxiety, evidence in clinical populations (e.g., Parkinson's disease, stroke), technology and training devices are discussed. Perturbation-based balance training is a promising approach to fall prevention. However, several fundamental and applied aspects of the approach need to be further investigated before it can be widely implemented in clinical practice.

Can a single session of treadmill-based slip training reduce daily life falls in community-dwelling older adults? A randomized controlled trial

BACKGROUND

Task-specific training with single-session overground slip simulation has shown to reduce real-life falls in older adults.

AIMS

The purpose of this study was to determine if fall-resisting behavior acquired from a single-session treadmill-based gait slip training could be retained to reduce older adults' falls in everyday living over a 6-month follow-up period.

METHODS

143 community-dwelling older adults (≥ 65 years old) were randomly assigned to either the treadmill-based gait slip training group (N = 73), in which participants were exposed to 40 unpredictable treadmill slips, or the control group (N = 70), in which participants walked on a treadmill at their comfortable speed. Participants reported their falls from the preceding year (through self-report history) and over the following 6 months (through fall diaries and monitored with phone calls).

RESULTS

There was no main effect of time (retrospective vs. prospective fall) and training (treadmill training vs. control) on fall reduction (p > 0.05 for both). The survival distributions of event of all-cause falls or slip falls were comparable between groups (p > 0.05 for both).

DISCUSSION

Unlike overground slip training where a single training session could significantly reduce everyday falls in a 6-month follow-up period, the results indicated that one treadmill-based gait slip training session by itself was unable to produce similar effects.

CONCLUSION

Further modification of the training protocol by increasing training dosage (e.g., number of sessions or perturbation intensity) may be necessary to enhance transfer to daily living. This study (NCT02126488) was registered on April 30, 2014.

Differences in muscle synergies among recovery responses limit inter-task generalisation of stability performance

Generalisation of adaptations is key to effective stability control facing variety of postural threats during daily life activity. However, in a previous study we could demonstrate that adaptations to stability control do not necessarily transfer to an untrained motor task. Here, we examined the dynamic stability and modular organisation of motor responses to different perturbations (i.e. unpredictable gait-trip perturbations and subsequent loss of anterior stability in a lean-and-release protocol) in a group of young and middle-aged adults (n = 57; age range 19-53 years) to detect potential neuromotor factors limiting transfer of adaptations within the stability control system. We hypothesized that the motor system uses different modular organisation in recovery responses to tripping and lean-and-release, which may explain lack in positive transfer of adaptations in stability control. After eight trip-perturbations participants increased their dynamic stability during the first recovery step (p < 0.001), yet they showed no significant improvement to the untrained lean-and-release transfer task compared to controls who did not undergo the perturbation exposure (p = 0.44). Regarding the neuromuscular control of responses, lower number of synergies (3 vs. 4) was found for the lean-and-release compared to the gait-trip perturbation task, revealing profound differences in both the timing and function of the recruited muscles to match the biomechanical specificity of different perturbations. Our results provide indirect evidence that the motor system uses different modular organisation in diverse perturbation responses, what possibly inhibits inter-task generalisation of adaptations in stability control.

Which Exercise Interventions Can Most Effectively Improve Reactive Balance in Older Adults? A Systematic Review and Network Meta-Analysis

Background

Reactive balance is the last line of defense to prevent a fall when the body loses stability, and beneficial effects of various exercise-based interventions on reactive balance in older adults have been reported. However, their pooled evidence on the relative effects has yet to be described.

Objective

To review and evaluate the comparative effectiveness of various exercise-based interventions on reactive balance in older adults.

Methods

Nine electronic databases and reference lists were searched from inception to August 2021. Eligibility criteria according to PICOS criteria were as follows: (1) population: older adults with the mean age of 65 years or above; (2) intervention and comparison: at least two distinct exercise interventions or one exercise intervention with a no-exercise controlled intervention (NE) compared in each trial; (3) outcome: at least one measure of reactive balance; (4) study: randomized controlled trial. The main network meta-analysis was performed on data from the entire older adult population, involving all clinical conditions as well as healthy older adults. Subgroup analyses stratified by characteristics of participants (healthy only) and reactive balance outcomes (simulated slip or trip while walking, simulated forward falls, being pushed or pulled, and movable platform) were also conducted.

Results

Thirty-nine RCTs (n = 1388) investigating 17 different types of exercise interventions were included in the network meta-analysis. Reactive balance training as a single intervention presented the highest probability (surface under the cumulative ranking (SUCRA) score) of being the best intervention for improving reactive balance and the greatest relative effects vs. NE in the entire sample involving all clinical conditions [SUCRA = 0.9; mean difference (95% Credible Interval): 2.7 (1.0 to 4.3)]. The results were not affected by characteristics of participants (i.e., healthy older adults only) or reactive balance outcomes.

Summary/Conclusion

The findings from the NMA suggest that a task-specific reactive balance exercise could be the optimal intervention for improving reactive balance in older adults, and power training can be considered as a secondary training exercise.

Proactive Modulation in the Spatiotemporal Structure of Muscle Synergies Minimizes Reactive Responses in Perturbed Landings

Stability training in the presence of perturbations is an effective means of increasing muscle strength, improving reactive balance performance, and reducing fall risk. We investigated the effects of perturbations induced by an unstable surface during single-leg landings on the mechanical loading and modular organization of the leg muscles. We hypothesized a modulation of neuromotor control when landing on the unstable surface, resulting in an increase of leg muscle loading. Fourteen healthy adults performed 50 single-leg landings from a 30 cm height onto two ground configurations: stable solid ground (SG) and unstable foam pads (UG). Ground reaction force, joint kinematics, and electromyographic activity of 13 muscles of the landing leg were measured. Resultant joint moments were calculated using inverse dynamics and muscle synergies with their time-dependent (motor primitives) and time-independent (motor modules) components were extracted via non-negative matrix factorization. Three synergies related to the touchdown, weight acceptance, and stabilization phase of landing were found for both SG and UG. When compared with SG, the motor primitive of the touchdown synergy was wider in UG (p < 0.001). Furthermore, in UG the contribution of gluteus medius increased (p = 0.015) and of gastrocnemius lateralis decreased (p < 0.001) in the touchdown synergy. Weight acceptance and stabilization did not show any statistically significant differences between the two landing conditions. The maximum ankle and hip joint moment as well as the rate of ankle, knee, and hip joint moment development were significantly lower (p < 0.05) in the UG condition. The spatiotemporal modifications of the touchdown synergy in the UG condition highlight proactive adjustments in the neuromotor control of landings, which preserve reactive adjustments during the weight acceptance and stabilization synergies. Furthermore, the performed proactive control in combination with the viscoelastic properties of the soft surface resulted in a reduction of the mechanical loading in the lower leg muscles. We conclude that the use of unstable surfaces does not necessarily challenge reactive motor control nor increase muscle loading per se. Thus, the characteristics of the unstable surface and the dynamics of the target task must be considered when designing perturbation-based interventions.

Balance Recoverability and Control of Bipedal Walkers with Foot Slip

Low-friction foot/ground contacts present a particular challenge for stable bipedal walkers. The slippage of the stance foot introduces complexity in robot dynamics and the general locomotion stability results cannot be applied directly. We relax the commonly used assumption of non-slip contact between the walker foot and the ground and examine bipedal dynamics under foot slip. Using a two-mass linear inverted pendulum model, we introduce the concept of balance recoverability and use it to quantify the balanced or fall-prone walking gaits. Balance recoverability also serves as the basis for the design of the balance recovery controller. We design the within- or multi-step recovery controller to assist the walker to avoid fall. The controller performance is validated through simulation results and robustness is demonstrated in the presence of measurement noises as well as variations of foot/ground friction conditions. In addition, the proposed methods and models are used to analyze the data from human walking experiments. The multiple subject experiments validate and illustrate the balance recoverability concept and analyses.

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.

Application of neuromuscular electrical stimulation on the support limb during reactive balance control in persons with stroke: a pilot study

The aim of the present study was to investigate the effect of the application of neuromuscular electrical stimulation to the quadriceps muscle of the paretic limb during externally induced stance perturbations on reactive balance control and on fall outcomes in people with chronic stroke. Ten participants experienced 12 stance treadmill perturbation trails, 6 forward balance perturbation trials and 6 backward balance perturbation trials. For each perturbation condition, three perturbation trials were delivered synchronized with neuromuscular electrical stimulation applied to the quadriceps of the paretic limb and three perturbation trials were delivered without stimulation. Behavioral outcome measures, such as incidence of laboratory falls and number of compensatory steps, kinematic outcome measures, such as margin of stability and minimum hip high values after the perturbation, step initiation time, step execution time and step length of the stepping leg were analyzed. The application of neuromuscular electrical stimulation on the paretic quadriceps between the range of 50 and 500 ms after stance forward and backward perturbations reduced the laboratory falls incidence (p < 0.05), improved stability values (p < 0.05) and reduced the hip height descent (p < 0.05) compared to the experimental condition in which participants were exposed to stance perturbations without neuromuscular electrical stimulation. Additionally, step initiation time of the recovery step was lower in neuromuscular electrical stimulation condition during the forward balance perturbation protocol. Our results showed that the application of neuromuscular electrical stimulation on the knee extensor muscles of the paretic limb reduces the incidence of laboratory falls, enhances reactive stability control and reduces vertical limb collapse after stance forward and backward perturbations in people with chronic stroke.

Perturbation-Based Balance Training Using Repeated Trips on a Walkway vs. Belt Accelerations on a Treadmill: A Cross-Over Randomised Controlled Trial in Community-Dwelling Older Adults

Background: Walkway and treadmill induced trips have contrasting advantages, for instance walkway trips have high-ecological validity whereas belt accelerations on a treadmill have high-clinical feasibility for perturbation-based balance training (PBT). This study aimed to (i) compare adaptations to repeated overground trips with repeated treadmill belt accelerations in older adults and (ii) determine if adaptations to repeated treadmill belt accelerations can transfer to an actual trip on the walkway.

Method: Thirty-eight healthy community-dwelling older adults underwent one session each of walkway and treadmill PBT in a randomised crossover design on a single day. For both conditions, 11 trips were induced to either leg in pseudo-random locations interspersed with 20 normal walking trials. Dynamic balance (e.g., margin of stability) and gait (e.g., step length) parameters from 3D motion capture were used to examine adaptations in the walkway and treadmill PBT and transfer of adaptation from treadmill PBT to a walkway trip.

Results: No changes were observed in normal (no-trip) gait parameters in both training conditions, except for a small (0.9 cm) increase in minimum toe elevation during walkway walks (P < 0.01). An increase in the margin of stability and recovery step length was observed during walkway PBT (P < 0.05). During treadmill PBT, an increased MoS, step length and decreased trunk sway range were observed (P < 0.05). These adaptations to treadmill PBT did not transfer to a walkway trip.

Conclusions: This study demonstrated that older adults could learn to improve dynamic stability by repeated exposure to walkway trips as well as treadmill belt accelerations. However, the adaptations to treadmill belt accelerations did not transfer to an actual trip. To enhance the utility of treadmill PBT for overground trip recovery performance, further development of treadmill PBT protocols is recommended to improve ecological authenticity.

Comparison of Lateral Perturbation-Induced Step Training and Hip Muscle Strengthening Exercise on Balance and Falls in Community-Dwelling Older Adults: A Blinded Randomized Controlled Trial

BACKGROUND

This factorial, assessor-blinded, randomized, and controlled study compared the effects of perturbation-induced step training (lateral waist-pulls), hip muscle strengthening, and their combination, on balance performance, muscle strength, and prospective falls among older adults.

METHODS

Community-dwelling older adults were randomized to 4 training groups. Induced step training (IST, n = 25) involved 43 progressive perturbations. Hip abduction strengthening (HST, n = 25) utilized progressive resistance exercises. Combined training (CMB, n = 25) included IST and HST, and the control performed seated flexibility/relaxation exercises (SFR, n = 27). The training involved 36 sessions for a period of 12 weeks. The primary outcomes were the number of recovery steps and first step length, and maximum hip abduction torque. Fall frequency during 12 months after training was determined.

RESULTS

Overall, the number of recovery steps was reduced by 31% and depended upon the first step type. IST and CMB increased the rate of more stable single lateral steps pre- and post-training than HST and SFR who used more multiple crossover and sequential steps. The improved rate of lateral steps for CMB exceeded the control (CMB/SFR rate ratio 2.68). First step length was unchanged, and HST alone increased hip torque by 25%. Relative to SFR, the fall rate ratios (falls/person/year) [95% confidence interval] were CMB 0.26 [0.07-0.90], IST 0.44 [0.18-1.08], and HST 0.30 (0.10-0.91).

CONCLUSIONS

Balance performance through stepping was best improved by combining perturbation and strength training and not strengthening alone. The interventions reduced future falls by 56%-74% over the control. Lateral balance perturbation training may enhance traditional programs for fall prevention.

Can Smartphone-Derived Step Data Predict Laboratory-Induced Real-Life Like Fall-Risk in Community- Dwelling Older Adults?

Background: As age progresses, decline in physical function predisposes older adults to high fall-risk, especially on exposure to environmental perturbations such as slips and trips. However, there is limited evidence of association between daily community ambulation, an easily modifiable factor of physical activity (PA), and fall-risk. Smartphones, equipped with accelerometers, can quantify, and display daily ambulation-related PA simplistically in terms of number of steps. If any association between daily steps and fall-risks is established, smartphones due to its convenience and prevalence could provide health professionals with a meaningful outcome measure, in addition to existing clinical measurements, to identify older adults at high fall-risk. Objective: This study aimed to explore whether smartphone-derived step data during older adults' community ambulation alone or together with commonly used clinical fall-risk measurements could predict falls following laboratory-induced real-life like slips and trips. Relationship between step data and PA questionnaire and clinical fall-risk assessments were examined as well. Methods: Forty-nine community-dwelling older adults (age 60-90 years) completed Berg Balance Scale (BBS), Activities-specific Balance Confidence scale (ABC), Timed Up-and-Go (TUG), and Physical Activity Scale for the Elderly (PASE). One-week and 1-month smartphone steps data were retrieved. Participants' 1-year fall history was noted. All participants' fall outcomes to laboratory-induced slip-and-trip perturbations were recorded. Logistic regression was performed to identify a model that best predicts laboratory falls. Pearson correlations examined relationships between study variables. Results: A model including age, TUG, and fall history significantly predicted laboratory falls with a sensitivity of 94.3%, specificity of 58.3%, and an overall accuracy of 85.1%. Neither 1-week nor 1-month steps data could predict laboratory falls. One-month steps data significantly positively correlated with BBS (r = 0.386, p = 0.006) and ABC (r = 0.369, p = 0.012), and negatively correlated with fall history (r _p = -0.293, p = 0.041). Conclusion: Older participants with fall history and higher TUG scores were more likely to fall in the laboratory. No association between smartphone steps data and laboratory fall-risk was established in our study population of healthy community-dwelling older adults which calls for further studies on varied populations. Although modest, results do reveal a relationship between steps data and functional balance deficits and fear of falls.

Can Treadmill Slip-Perturbation Training Reduce Longer-Term Fall Risk Upon Overground Slip Exposure?

The purpose was to examine and compare the longer-term generalization between 2 different practice dosages for a single-session treadmill slip-perturbation training when reexposed to an overground slip 6 months later. A total of 45 older adults were conveniently assigned to either 24 or 40 slip-like treadmill perturbation trials or a third control group. Overground slips were given immediately after initial training, and at 6 months after initial training in order to examine immediate and longer-term effects. The performance (center of mass stability and vertical limb support) and fall percentage from the laboratory-induced overground slips (at initial posttraining and at 6 mo) were measured and compared between groups. Both treadmill slip-perturbation groups showed immediate generalization at the initial posttraining test and longer-term generalization at the 6-month retest. The higher-practice-dosage group performed significantly better than the control group (P < .05), with no difference between the lower-practice-dosage and the control groups at the 6-month retest (P > .05). A single session of treadmill slip-perturbation training showed a positive effect for reducing older adults' fall risk for laboratory-induced overground slips. A higher-practice dosage of treadmill slip perturbations could be more beneficial for further reducing fall risk.

The retention of fall-resisting behavior derived from treadmill slip-perturbation training in community-dwelling older adults

The purpose of this study was to determine whether and to what extent the immediate generalization of treadmill slip-perturbation training could be retained over 6 months to resist overground slip-induced falls. Four protocols (Tc: treadmill control; Tt: treadmill slip-perturbation training; Oc: overground control; Ot: overground slip-perturbation training) from two randomized controlled trials were compared in which two training protocols were executed with single-session repeated slip-perturbation training on the treadmill or overground context, while two control protocols were executed without repeated training. A total of 152 community-dwelling older adults (≥ 65 years) who were trained by one of the four protocols and tested by an overground slip in the initial session attended a retest session 6 months later. Falls were detected by a load cell. Data collected from motion analysis system and force plates were used to calculate stability. Tt group had no significant change in fall incidence from initial post-training test to retest. Tt group had significantly lower fall incidence (p < 0.05) and higher reactive stability (p < 0.05) than Tc group in retest. Tt group had significantly higher fall incidence (p < 0.05) and lower reactive stability (p < 0.01) than Ot group. The generalization of a single session of treadmill slip-perturbation training to overground slip resulted in inferior outcomes compared with overground slip-perturbation training (absolute retention), although the training generalization could be retained over 6 months (relative retention). Thus, treadmill slip-perturbation training could be more convenient to use if future dose-response studies indicate better or equal efficacy to overground slip-perturbation training.

A Motor Learning Approach to Reducing Fall-Related Injuries

Falls are the leading cause of injury related death in older adults. In this piece, a motor learning lens is applied to falls, and falls are viewed as three interdependent phases: 1) destabilization, 2) descent, and 3) impact. This review examines how movements can be performed in the descent and impact phases to potentially reduce fall-related injuries. The evidence that movements performed during the descent and impact phases are voluntary motor skills that can be learned by older adults is reviewed. Data from young adult and older adult studies suggest that safe landing strategies can reduce impact force, are voluntary, and are learnable. In conclusion, safe landing strategies may provide a complimentary approach to reduce fall-related injuries.

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).

Retention and generalizability of balance recovery response adaptations from trip perturbations across the adult life span

For human locomotion, varying environments require adjustments of the motor system. We asked whether age affects gait balance recovery adaptation, its retention over months, and the transfer of adaptation to an untrained reactive balance task. Healthy adults (26 young, 27 middle-aged, and 25 older; average ages 24, 52, and 72 yr, respectively) completed two tasks. The primary task involved treadmill walking: either unperturbed (control; n = 39) or subject to unexpected trip perturbations (training; n = 39). A single trip perturbation was repeated after a 14-wk retention period. The secondary transfer task, before and after treadmill walking, involved sudden loss of balance in a lean-and-release protocol. For both tasks, the anteroposterior margin of stability (MoS) was calculated at foot touchdown. For the first (i.e., novel) trip, older adults required one more recovery step ( P = 0.03) to regain positive MoS compared with younger, but not middle-aged, adults. However, over several trip perturbations, all age groups increased their MoS for the first recovery step to a similar extent (up to 70%) and retained improvements over 14 wk, although a decay over time was found for older adults ( P = 0.002; middle-aged showing a tendency for decay: P = 0.076). Thus, although adaptability in reactive gait stability control remains effective across the adult life span, retention of adaptations over time appears diminished with aging. Despite these robust adaptations, the perturbation training group did not show superior improvements in the transfer task compared with age-matched controls (no differences in MoS changes), suggesting that generalizability of acquired fall-resisting skills from gait-perturbation training may be limited.

NEW & NOTEWORTHY The human neuromotor system preserves its adaptability across the adult life span. However, although adaptability in reactive gait stability control remains effective as age increases, retention of recovery response adaptations over time appears to be reduced with aging. Furthermore, acquired fall-resisting skills from single-session perturbation training seem task specific, which may limit the generalizability of such training to the variety of real-life falls.

Treadmill-gait slip training in community-dwelling older adults: mechanisms of immediate adaptation for a progressive ascending-mixed-intensity protocol

The study purpose was to investigate whether older adults could improve their stability against a backward loss of balance (BLOB) after receiving repeated treadmill slips during walking and to see how such adaptive changes would be affected by practice dosage (combination of slip intensity and the number of slips at each intensity). Twenty-five healthy community-dwelling older adults received forty treadmill slips given over eleven blocks at five intensities (P1-P1-P2-P3-P4-P5-P4-P5-P5-P3-P1, larger number indicating higher intensity). Center of mass (COM) stability was calculated as the shortest distance of the instantaneous COM position and velocity relative to the base of support (BOS) from a theoretical threshold for BLOB (larger stability value indicated a better stability against BLOB). Stability, step length, and trunk angle were measured before and after slip onset to reflect proactive and reactive control, respectively. The first slips at each intensity block (i.e., P1, P3, P4, and P5) were compared with the first slips in the last blocks at those intensities to examine main effects of training dosage (intensity and repetition). Improvements in proactive and reactive stability were more pronounced for receiving more slips at larger intensities than fewer slips at smaller intensities. Older adults only demonstrated partial positive scaling effects to proactively, not reactively, establish a more stable initial COM state. The improved proactive stability was associated with an anterior shift of COM position relative to the BOS, resulting from a shorter pre-slip step length. The improved reactive stability was associated with an anterior shift of COM position, resulting from a larger compensatory step length and a faster COM velocity relative to the BOS. Our findings indicated that treadmill-gait slip perturbations elicited similar proactive and reactive control to that from over-ground slip perturbations, but greater slip intensity and repetition might yield more immediate adaptive improvements.

Does severity of motor impairment affect reactive adaptation and fall-risk in chronic stroke survivors?

Background

A single-session of slip-perturbation training has shown to induce long-term fall risk reduction in older adults. Considering the spectrum of motor impairments and deficits in reactive balance after a cortical stroke, we aimed to determine if chronic stroke survivors could acquire and retain reactive adaptations to large slip-like perturbations and if these adaptations were dependent on severity of motor impairment.

Methods

Twenty-six chronic stroke participants were categorized into high and low-functioning groups based on their Chedoke-McMaster-Assessment scores. All participants received a pre-training, slip-like stance perturbation at level-III (highest intensity/acceleration) followed by 11 perturbations at a lower intensity (level-II). If in early phase, participants experienced > 3/5 falls, they were trained at a still lower intensity (level-I). Post-training, immediate scaling and short-term retention at 3 weeks post-training was examined. Perturbation outcome and post-slip center-of-mass (COM) stability was analyzed.

Results

On the pre-training trial, 60% of high and 100% of low-functioning participants fell. High-functioning group tolerated and adapted at training-intensity level-II but low-functioning group were trained at level-I (all had > 3 falls on level-II). At respective training intensities, both groups significantly lowered fall incidence from 1st through 11th trials, with improved post-slip stability and anterior shift in COM position, resulting from increased compensatory step length. Both groups demonstrated immediate scaling and short-term retention of the acquired stability control.

Conclusion

Chronic stroke survivors are able to acquire and retain adaptive reactive balance skills to reduce fall risk. Although similar adaptation was demonstrated by both groups, the low-functioning group might require greater dosage with gradual increment in training intensity.