A systematic review of gait perturbation paradigms for improving reactive stepping responses and falls risk among healthy older adults

Effect of Multisession Progressive Gait-Slip Training on Fall-Resisting Skills of People with Chronic Stroke: Examining Motor Adaptation in Reactive Stability

Background: This study examined whether a multisession gait-slip training could enhance reactive balance control and fall-resisting skills of people with chronic stroke (PwCS). Methods: A total of 11 PwCS underwent a four-week treadmill-based gait-slip training (four sessions). Pre- and post-training assessment was performed on six intensities of gait-slips (levels 1–6). Training consisted of 10 blocks of each progressively increasing intensity (four trials per block) until participants fell at >2 trials per block (fall threshold). In the next session, training began at a sub-fall threshold and progressed further. Fall outcome and threshold, number of compensatory steps, multiple stepping threshold, progression to higher intensities, pre- and post-slip center of mass (CoM), state stability, clinical measures, and treadmill walking speed were analyzed. Results: Post-training, PwCS demonstrated a reduction in falls and compensatory steps on levels 5 and 6 (p < 0.05) compared to pre-training. While an increase in pre-slip stability was limited to level 6 (p < 0.05), improvement in post-slip stability at lift-off was noted on levels 2, 3, and 5 (p < 0.05) along with improved post-slip minimum stability on levels 5 and 6 (p < 0.05). Post-training demonstrated improved fall (p < 0.05) and multiple stepping thresholds (p = 0.05). While most participants could progress to level 4 between the first and last training sessions, more participants progressed to level 6 (p < 0.05). Participants’ treadmill walking speed increased (p < 0.05); however, clinical measures remained unchanged (p > 0.05). Conclusions: Multisession, progressively increasing intensity of treadmill-based gait-slip training appears to induce significant adaptive improvement in falls, compensatory stepping, and postural stability among PwCS.

Unconstrained slip mechanics and stepping reactions depend on slip onset timing

Slips can occur at any time during stance. Accordingly, time-dependent tangential ground reaction forces likely produce a diverse range of slipping foot mechanics when traction is lost, thus requiring flexible recovery strategies to prevent falls. However, previous research has focused on slip onset in early stance, often with experimental anteroposterior constraints on the slipping foot, despite the diversity of environmental slips and falls. This study aimed to determine the effects of slip onset time on slip direction, severity (distance and velocity), and compensatory stepping responses. Ten young adults received slipping perturbations at different times during the stance phase of walking via a wearable device that reduces available friction while allowing the slipping foot to slide freely within the horizontal plane. Slip direction, distance, and peak velocity, compensatory step direction and distance, and upper body angular momentum magnitude and plane of rotation were derived from kinematic data. All outcome measurements significantly correlated with the time of slip onset. Slip direction and the plane of rotation of angular momentum deviated widely from the sagittal plane, exhibiting laterally-directed components exceeding those in the anteroposterior direction. As slip onset occurred later in stance, slip severity decreased while compensatory steps became longer and progressed from a posterior to anterior placement. These results provide insight into critical times within stance when slips are most severe, and into the diversity of slipping mechanics caused by changes in slip onset time.

Margin of Stability May Be Larger and Less Variable during Treadmill Walking Versus Overground

Margin of stability (MOS) is considered a measure of mechanical gait stability. Due to broad application of treadmills in gait assessment experiments, we aimed to determine if walking on a treadmill vs. overground would affect MOS during three speed-matched conditions. Eight healthy young participants walked on a treadmill and overground at Slow, Preferred, and Fast speed-matched conditions. The mean and variability (standard deviation) of the MOS in anterior-posterior and mediolateral directions at heel contact were calculated. Anterior-posterior and mediolateral mean MOS values decreased with increased speed for both overground and treadmill; although mediolateral mean MOS was always wider on the treadmill compared to overground. Due to lack of optic flow and different proprioceptive inputs during treadmill walking, subjects may employ strategies to increase their lateral stability on treadmill compared to overground. Anterior-posterior MOS variability increased with speed overground, while it did not change on treadmill, which might be due to the fixed speed of treadmill. Whereas, lateral variability on both treadmill and overground was U-shaped. Walking at preferred speed was less variable (may be interpreted as more stable) laterally, compared to fast and slow speeds. Caution should be given when interpreting MOS between modes and speeds of walking. As sagittal plane walking is functionally unstable, this raises the consideration as to the meaningfulness of using MOS as a global measure of gait stability in this direction.

Neural Control of Human Locomotor Adaptation: Lessons about Changes with Aging

Walking patterns are adaptable in response to different environmental demands, which requires neural input from spinal and supraspinal structures. With an increase in age, there are changes in walking adaptation and in the neural control of locomotion, but the age-related changes in the neural control of locomotor adaptation is unclear. The purpose of this narrative review is to establish a framework where the age-related changes of neural control of human locomotor adaptation can be understood in terms of reactive feedback and predictive feedforward control driven by sensory feedback during locomotion. We parse out the effects of aging on (a) reactive adaptation to split-belt walking, (b) predictive adaptation to split-belt walking, (c) reactive visuomotor adaptation, and (d) predictive visuomotor adaptation, and hypothesize that specific neural circuits are influenced differentially with age, which influence locomotor adaptation. The differences observed in the age-related changes in walking adaptation across different locomotor adaptation paradigms will be discussed in light of the age-related changes in the neural mechanisms underlying locomotion.

Adaptability to Balance Perturbations During Walking as a Potential Marker of Falls History in Older Adults

Given that falls most commonly occur during walking due to unexpected balance perturbations like trips and slips, walking-based balance assessment including walking stability and adaptability to such perturbations could be beneficial for fall risk assessment in older adults. This cross-sectional study reanalyzed data from two larger studies conducted with the same walking protocol. Participants completed unperturbed walking trials at speeds of 0.4 m/s up to 1.8 m/s in 0.2 m/s steps. Ten unannounced treadmill belt acceleration perturbations were then applied while participants walked at equivalent stability, assessed using the margins of stability. Retrospective (12 months) falls incidence was collected to divide participants into people with and without a history of falls. Twenty older adults (mean age 70.2 ± 2.9 years) were included in this analysis; eight people with one or more recent falls and 12 people without, closely matched by sex, age and height. No significant differences were found in unperturbed walking parameters or their variability. Overall perturbation-recovery step behavior differed slightly (not statistically significant) between the groups after the first perturbation and differences became more pronounced and significant after repetition of perturbations. The No-Falls group significantly reduced the number of recovery steps needed across the trials, whereas the Falls group did not show these improvements. People with a previous fall tended to have slightly delayed and more variable recovery responses after perturbation compared to non-fallers. Non-fallers demonstrate more signs of adaptability to repeated perturbations. Adaptability may give a broader indication of the ability of the locomotor system to respond and improve responses to sudden walking perturbations than unperturbed walking variability or recovery to a single novel perturbation. Adaptability may thus be a more useful marker of falls history in older adults and should be considered in further research.

Patterns of whole-body muscle activations following vertical perturbations during standing and walking

BACKGROUND

Falls commonly occur due to losses of balance associated with vertical body movements (e.g. reacting to uneven ground, street curbs). Research, however, has focused on horizontal perturbations, such as forward and backward translations of the standing surface. This study describes and compares muscle activation patterns following vertical and horizontal perturbations during standing and walking, and investigates the role of vision during standing postural responses.

METHODS

Fourteen healthy participants (ten males; 27±4 years-old) responded to downward, upward, forward, and backward perturbations while standing and walking in a virtual reality (VR) facility containing a moveable platform with an embedded treadmill; participants were also exposed to visual perturbations in which only the virtual scenery moved. We collected bilateral surface electromyography (EMG) signals from 8 muscles (tibialis anterior, rectus femoris, rectus abdominis, external oblique, gastrocnemius, biceps femoris, paraspinals, deltoids). Parameters included onset latency, duration of activation, and activation magnitude. Standing perturbations comprised dynamic-camera (congruent), static-camera (incongruent) and eyes-closed sensory conditions. ANOVAs were used to compare the effects of perturbation direction and sensory condition across muscles.

RESULTS

Vertical perturbations induced longer onset latencies and shorter durations of activation with lower activation magnitudes in comparison to horizontal perturbations (p<0.0001). Downward perturbations while standing generated earlier activation of anterior muscles to facilitate flexion (for example, p=0.0005 and p=0.0021 when comparing the early activators, rectus femoris and tibialis anterior, to a late activator, the paraspinals), whereas upward perturbations generated earlier activation of posterior muscles to facilitate extension (for example, p<0.0001 and p=0.0004, when comparing the early activators, biceps femoris and gastrocnemius, to a late activator, the rectus abdominis). Static-camera conditions induced longer onset latencies (p=0.0085 and p<0.0001 compared to eyes-closed and dynamic-camera conditions, respectively), whereas eyes-closed conditions induced longer durations of activation (p=0.0001 and p=0.0008 compared to static-camera and dynamic-camera, respectively) and larger activation magnitudes. During walking, downward perturbations promptly activated contralateral trunk and deltoid muscles (e.g., p=0.0036 for contralateral deltoid versus a late activator, the ipsilateral tibialis anterior), and upward perturbations triggered early activation of trunk flexors (e.g., p=0.0308 for contralateral rectus abdominis versus a late activator, the ipsilateral gastrocnemius). Visual perturbations elicited muscle activation in 67.7% of trials.

CONCLUSION

Our results demonstrate that vertical (vs. horizontal) perturbations generate unique balance-correcting muscle activations, which were consistent with counteracting vertical body extension induced by downward perturbations and vertical body flexion induced by upward perturbations. Availability of visual input appears to affect response efficiency, and incongruent visual input can adversely affect response triggering. Our findings have clinical implications for the design of robotic exoskeletons (to ensure user safety in dynamic balance environments) and for perturbation-based balance and gait rehabilitation.

Temporal accuracy of gait after metronome practice

Humans readily entrain their movements to a beat, including matching their gait to a prescribed tempo. Rhythmic auditory cueing tasks have been used to enhance stepping behavior in a variety of clinical populations. However, there is limited understanding of how temporal accuracy of gait changes over practice in healthy young adults. In this study, we examined how inter-step interval and cadence deviated from slow, medium, and fast tempos across steps within trials, across trials within blocks, and across two blocks that bookended a period of practice of walking to each tempo. Participants were accurate in matching the tempo at the slow and medium tempos, while they tended to lag behind the beat at the fast tempo. We also found that participants showed no substantial improvement across steps and trials, nor across blocks, suggesting that participants had a robust ability to entrain their gait to the specified metronome tempo. However, we did find that participants habituated to the prescribed tempo, showing self-paced gait that was faster than self-paced baseline gait after the fast tempo, and slower than self-paced baseline gait after the slow tempo. These findings might represent an "after-effect" in the temporal domain, akin to after-effects consistently shown in other sensorimotor tasks. This knowledge of how healthy participants entrain their gait to temporal cues may have important implications in understanding how clinical populations acquire and modify their gait in rhythmic auditory cueing tasks.

Promoting Generalized Learning in Balance Recovery Interventions

Recent studies have shown balance recovery can be enhanced via task-specific training, referred to as perturbation-based balance training (PBT). These interventions rely on principles of motor learning where repeated exposure to task-relevant postural perturbations results in more effective compensatory balance responses. Evidence indicates that compensatory responses trained using PBT can be retained for many months and can lead to a reduction in falls in community-dwelling older adults. A notable shortcoming with PBT is that it does not transfer well to similar but contextually different scenarios (e.g., falling sideways versus a forward trip). Given that it is not feasible to train all conditions in which someone could fall, this limited transfer presents a conundrum; namely, how do we best use PBT to appropriately equip people to deal with the enormous variety of fall-inducing scenarios encountered in daily life? In this perspective article, we draw from fields of research that explore how general learning can be promoted. From this, we propose a series of methods, gleaned from parallel streams of research, to inform and hopefully optimize this emerging field where people receive training to specifically improve their balance reactions.

Acceleration Gait Measures as Proxies for Motor Skill of Walking: A Narrative Review

In adults 65 years or older, falls or other neuromotor dysfunctions are often framed as walking-related declines in motor skill; the frequent occurrence of such decline in walking-related motor skill motivates the need for an improved understanding of the motor skill of walking. Simple gait measurements, such as speed, do not provide adequate information about the quality of the body motion's translation during walking. Gait measures from accelerometers can enrich measurements of walking and motor performance. This review article will categorize the aspects of the motor skill of walking and review how trunk-acceleration gait measures during walking can be mapped to motor skill aspects, satisfying a clinical need to understand how well accelerometer measures assess gait. We will clarify how to leverage more complicated acceleration measures to make accurate motor skill decline predictions, thus furthering fall research in older adults.

The balance function is associated with frailty in community-dwelling older women

Conditions underlying balance impairment should be identified to improve knowledge regarding clinical interventions for frail older adults. This study aims to explore the relationship between balance functions and frailty by using the brief balance evaluation systems test (BESTest), which can assess biomechanical constraints, stability limits/verticality, anticipatory postural adjustments (APAs), reactive postural responses, sensory orientation and stability in gait. A total of 75 community-dwelling older women were included in this cross-sectional study. We evaluated frailty by using the Kihon checklist and assessed the participants' balance functions by using the Brief BESTest. We performed the Mann-Whitney U test and receiver operating characteristic curve analysis to compare each balance function between frail and nonfrail participants. Twenty-two of the 75 (29.3%) participants were included in the frailty group. We noted significant differences between the frailty and nonfrailty groups with regard to stability limit, APAs, sensory orientation, and stability in gait (P = 0.010, 0.001, 0.008 and <0.001, respectively). In terms of determining frailty and nonfrailty, APAs and stability in gait were moderately accurate (the area under the curve = 0.730 and 0.713, respectively). APAs showed the highest sensitivity (0.864), whereas stability limits, sensory orientation, and stability in gait showed the highest specificity (0.943, 0.849 and 0.868, respectively). Thus, frail and nonfrail older adults showed significantly different balance functions, such as stability limits, APAs, sensory orientation and stability in gait. The Brief BESTest is useful for evaluating balance functions in relation to frailty.

Examining Different Motor Learning Paradigms for Improving Balance Recovery Abilities Among Older Adults, Random vs. Block Training-Study Protocol of a Randomized Non-inferiority Controlled Trial

Introduction: Falls are the leading cause of fatal and nonfatal injuries among older adults. Studies showed that older adults can reduce the risk of falls after participation in an unexpected perturbation-based balance training (PBBT), a relatively novel approach that challenged reactive balance control. This study aims to investigate the effect of the practice schedule (i.e., contextual interference) on reactive balance function and its transfer to proactive balance function (i.e., voluntary step execution test and Berg balance test). Our primary hypothesis is that improvements in reactive balance control following block PBBT will be not inferior to the improvements following random PBBT.

Methods and Analysis: This is a double-blind randomized controlled trial. Fifty community-dwelling older adults (over 70 years) will be recruited and randomly allocated to a random PBBT group (n = 25) or a block PBBT group (n = 25). The random PBBT group will receive eight training sessions over 4 weeks that include unexpected machine-induced perturbations of balance during hands-free treadmill walking. The block PBBT group will be trained by the same perturbation treadmill system, but only one direction will be trained in each training session, and the direction of the external perturbations will be announced. Both PBBT groups (random PBBT and block PBBT) will receive a similar perturbation intensity during training (which will be customized to participant’s abilities), the same training period, and the same concurrent cognitive tasks during training. The generalization and transfer of learning effects will be measured by assessing the reactive and proactive balance control during standing and walking before and after 1 month of PBBT, for example, step and multiple steps and fall thresholds, Berg balance test, and fear of falls. The dependent variable will be rank transformed prior to conducting the analysis of covariance (ANCOVA) to allow for nonparametric analysis.

Discussion: This research will explore which of the balance retraining paradigms is more effective to improve reactive balance and proactive balance control in older adults (random PBBT vs. block PBBT) over 1 month. The research will address key issues concerning balance retraining: older adults’ neuromotor capacities to optimize training responses and their applicability to real-life challenges.

Clinical Trial Registration: Helsinki research ethics approval has been received (Soroka Medical Center approval #0396-16-SOR; MOH_2018-07-22_003536; www.ClinicalTrials.gov, NCT04455607).

Repeated exposure to tripping like perturbations elicits more precise control and lower toe clearance of the swinging foot during steady walking

Controlling minimum toe clearance (MTC) is considered an important factor in preventing tripping. In the current study, we investigated modifications of neuro-muscular control underlying toe clearance during steady locomotion induced by repeated exposure to tripping-like perturbations of the right swing foot. Fourteen healthy young adults (mean age 26.4 ± 3.1 years) participated in the study. The experimental protocol consisted of three identical trials, each involving three phases: steady walking (baseline), perturbation, and steady walking (post-perturbation). During the perturbation, participants experienced 30 tripping-like perturbations at unexpected timing delivered by a custom-made mechatronic perturbation device. The temporal parameters (cadence and stance phase_%), mean, and standard deviation of MTC were computed across approximately 90 strides collected during both baseline and post-perturbation phases, for all trials. The effects of trial (three levels), phase (two levels: baseline and post-perturbation) and foot (two levels: right and left) on the outcome variables were analyzed using a three-way repeated measures analysis of variance. The results revealed that exposure to repeated trip-like perturbations modified MTC toward more precise control and lower toe clearance of the swinging foot, which appeared to reflect both the expectation of potential forthcoming perturbations and a quicker compensatory response in cases of a lack of balance. Moreover, locomotion control enabled subjects to maintain symmetric rhythmic features during post-perturbation steady walking. Finally, the effects of exposure to perturbation quickly disappeared among consecutive trials.

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.

Development and piloting of a perturbation stationary bicycle robotic system that provides unexpected lateral perturbations during bicycling (the PerStBiRo system)

Background

Balance control, and specifically balance reactive responses that contribute to maintaining balance when balance is lost unexpectedly, is impaired in older people. This leads to an increased fall risk and injurious falls. Improving balance reactive responses is one of the goals in fall-prevention training programs. Perturbation training during standing or treadmill walking that specifically challenges the balance reactive responses has shown very promising results; however, only older people who are able to perform treadmill walking can participate in these training regimes. Thus, we aimed to develop, build, and pilot a mechatronic Perturbation Stationary Bicycle Robotic system (i.e., PerStBiRo) that can challenge balance while sitting on a stationary bicycle, with the aim of improving balance proactive and reactive control.

Methods

This paper describes the development, and building of the PerStBiRo using stationary bicycles. In addition, we conducted a pilot randomized control trial (RCT) with 13 older people who were allocated to PerStBiRo training (N = 7) versus a control group, riding stationary bicycles (N = 6). The Postural Sway Test, Berg Balance Test (BBS), and 6-min Walk Test were measured before and after 3 months i.e., 20 training sessions.

Results

The PerStBiRo System provides programmed controlled unannounced lateral balance perturbations during stationary bicycling. Its software is able to identify a trainee’s proactive and reactive balance responses using the Microsoft Kinect™ system. After a perturbation, when identifying a trainee’s trunk and arm reactive balance response, the software controls the motor of the PerStBiRo system to stop the perturbation. The pilot RCT shows that, older people who participated in the PerStBiRo training significantly improved the BBS (54 to 56, p = 0.026) and Postural Sway velocity (20.3 m/s to 18.3 m/s, p = 0.018), while control group subject did not (51.0 vs. 50.5, p = 0.581 and 15 m/s vs. 13.8 m/s, p = 0.893, respectively), 6MWT tended to improve in both groups.

Conclusions

Our participants were able to perform correct balance proactive and reactive responses, indicating that older people are able to learn balance trunk and arm reactive responses during stationary bicycling. The pilot study shows that these improvements in balance proactive and reactive responses are generalized to performance-based measures of balance (BBS and Postural Sway measures).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-021-02015-1.

The Effects of Bicycle Simulator Training on Anticipatory and Compensatory Postural Control in Older Adults: Study Protocol for a Single-Blind Randomized Controlled Trial

Background: Falls are the leading cause of fatal and non-fatal injuries among older adults. Perturbation-Based-Balance Training (PBBT) is a promising approach to reduce fall rates by improving reactive balance responses. PBBT programs are designed for older adults who are able to stand and walk on a motorized treadmill independently. However, frail older adults, whose fall rates are higher, may not have this ability and they cannot participate. Thus, there is a critical need for innovative perturbation exercise programs to improve reactive balance and reduce the fall risks among older adults in a wider range of functioning. Trunk and arms are highly involved in reactive balance reactions. We aim to investigate whether an alternative PBBT program that provides perturbations during hands-free bicycling in a sitting position, geared to improve trunk and arm reactive responses, can be transferred to reduce fall risks and improve balance function among pre-frail older adults.

Methods: In a single-blinded randomized-controlled trial, 68 community-dwelling pre-frail older adults are randomly allocated into two intervention groups. The experimental group receives 24-PBBT sessions over 12-weeks that include self-induced internal and machine-induced external unannounced perturbations of balance during hands-free pedaling on a bicycle-simulator system, in combination with cognitive dual-tasks. The control group receives 24 pedaling sessions over 12-weeks by the same bicycle-simulator system under the same cognitive dual-tasks, but without balance perturbations. Participants' reactive and proactive balance functions and gait function are assessed before and after the 12-week intervention period (e.g., balance reactive responses and strategies, voluntary step execution test, postural stability in upright standing, Berg Balance Test, Six-meter walk test, as well as late life function and fear of falling questionnaires).

Discussion: This research addresses two key issues in relation to balance re-training: (1) generalization of balance skills acquired through exposure to postural perturbations in a sitting position investigating the ability of pre-frail older adults to improve reactive and proactive balance responses in standing and walking, and (2) the individualization of perturbation training to older adults' neuromotor capacities in order to optimize training responses and their applicability to real-life challenges.

Clinical Trial Registration:www.clinicaltrials.gov, NCT03636672 / BARZI0104; Registered: July 22, 2018; Enrolment of the first participant March: 1, 2019. See Supplementary File.

Objective falls-risk prediction using wearable technologies amongst patients with and without neurogenic gait alterations: a narrative review of clinical feasibility

OBJECTIVES

The present narrative review aims to collate the literature regarding the current use of wearable gait measurement devices for falls-risk assessment in neurological and non-neurological populations. Thereby, this review seeks to determine the extent to which the aforementioned barriers inhibit clinical use.

BACKGROUND

Falls contribute a significant disease burden in most western countries, resulting in increased morbidity and mortality with substantial therapeutic costs. The recent development of gait analysis sensor technologies has enabled quantitative measurement of several gait features related to falls risk. However, three main barriers to implementation exist: accurately measuring gait-features associated with falls, differentiating between fallers and non-fallers using these gait features, and the accuracy of falls predictive algorithms developed using these gait measurements.

METHODS

Searches of Medline, PubMed, Embase and Scopus were screened to identify 46 articles relevant to the present study. Studies performing gait assessment using any wearable gait assessment device and analysing correlation with the occurrence of falls during a retrospective or prospective study period were included. Risk of Bias was assessed using the Centre for Evidence Based Medicine (CEBM) Criteria.

CONCLUSIONS

Falls prediction algorithms based entirely, or in-part, on gait data have shown comparable or greater success of predicting falls than existing stratification scoring systems such as the 10-meter walk test or timed-up-and-go. However, data is lacking regarding their accuracy in neurological patient populations. Inertial measurement units (IMU) have displayed competency in obtaining and interpreting gait metrics relevant to falls risk. They have the potential to enhance the accuracy and efficiency of falls risk assessment in inpatient and outpatient setting.

Comparison of a Deep Learning-Based Pose Estimation System to Marker-Based and Kinect Systems in Exergaming for Balance Training

Using standard digital cameras in combination with deep learning (DL) for pose estimation is promising for the in-home and independent use of exercise games (exergames). We need to investigate to what extent such DL-based systems can provide satisfying accuracy on exergame relevant measures. Our study assesses temporal variation (i.e., variability) in body segment lengths, while using a Deep Learning image processing tool (DeepLabCut, DLC) on two-dimensional (2D) video. This variability is then compared with a gold-standard, marker-based three-dimensional Motion Capturing system (3DMoCap, Qualisys AB), and a 3D RGB-depth camera system (Kinect V2, Microsoft Inc). Simultaneous data were collected from all three systems, while participants (N = 12) played a custom balance training exergame. The pose estimation DLC-model is pre-trained on a large-scale dataset (ImageNet) and optimized with context-specific pose annotated images. Wilcoxon's signed-rank test was performed in order to assess the statistical significance of the differences in variability between systems. The results showed that the DLC method performs comparably to the Kinect and, in some segments, even to the 3DMoCap gold standard system with regard to variability. These results are promising for making exergames more accessible and easier to use, thereby increasing their availability for in-home exercise.

Deep Neural Network for Slip Detection on Ice Surface

Slip-induced falls are among the most common causes of major occupational injuries and economic loss in Canada. Identifying the risk factors associated with slip events is key to developing preventive solutions to reduce falls. One factor is the slip-resistance quality of footwear, which is fundamental to reducing the number of falls. Measuring footwear slip resistance with the recently developed Maximum Achievable Angle (MAA) test requires a trained researcher to identify slip events in a simulated winter environment. The human capacity for information processing is limited and human error is natural, especially in a cold environment. Therefore, to remove conflicts associated with human errors, in this paper a deep three-dimensional convolutional neural network is proposed to detect the slips in real-time. The model has been trained by a new dataset that includes data from 18 different participants with various clothing, footwear, walking directions, inclined angles, and surface types. The model was evaluated on three types of slips: Maxi-slip, midi-slip, and mini-slip. This classification is based on the slip perception and recovery of the participants. The model was evaluated based on both 5-fold and Leave-One-Subject-Out (LOSO) cross validation. The best accuracy of 97% was achieved when identifying the maxi-slips. The minimum accuracy of 77% was achieved when classifying the no-slip and mini-slip trials. The overall slip detection accuracy was 86% with sensitivity and specificity of 81% and 91%, respectively. The overall accuracy dropped by about 2% in LOSO cross validation. The proposed slip detection algorithm is not only beneficial for footwear manufactures to improve their footwear slip resistance quality, but it also has other potential applications, such as improving the slip resistance properties of flooring in healthcare facilities, commercial kitchens, and oil drilling platforms.

Age-related differences in gait adaptations during overground walking with and without visual perturbations using a virtual reality headset

Older adults have difficulty adapting to new visual information, posing a challenge to maintain balance during walking. Virtual reality can be used to study gait adaptability in response to discordant sensorimotor stimulations. This study aimed to investigate age-related modifications and propensity for visuomotor adaptations due to continuous visual perturbations during overground walking in a virtual reality headset. Twenty old and twelve young subjects walked on an instrumented walkway in real and virtual environments while reacting to antero-posterior and medio-lateral oscillations of the visual field. Mean and variability of spatiotemporal gait parameters were calculated during the first and fifth minutes of walking. A 3-way mixed-design ANOVA was performed to determine the main and interaction effects of group, condition and time. Both groups modified gait similarly, but older adults walked with shorter and slower strides and did not reduce stride velocity or increase stride width variability during medio-lateral perturbations. This may be related to a more conservative and anticipatory strategy as well as a reduced perception of the optic flow. Over time, participants adapted similarly to the perturbations but only younger participants reduced their stride velocity variability. Results provide novel evidence of age- and context-dependent visuomotor adaptations in response to visual perturbations during overground walking and may help to establish new methods for early identification and remediation of gait deficits.

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.

Adaptation of balancing behaviour during continuous perturbations of stance. Supra-postural visual tasks and platform translation frequency modulate adaptation rate

When humans are administered continuous and predictable perturbations of stance, an adaptation period precedes the steady state of balancing behaviour. Little information is available on the modulation of adaptation by vision and perturbation frequency. Moreover, performance of supra-postural tasks may modulate adaptation in as yet unidentified ways. Our purpose was to identify differences in adaptation associated to distinct visual tasks and perturbation frequencies. Twenty non-disabled adult volunteers stood on a platform translating 10 cm in antero-posterior (AP) direction at low (LF, 0.18 Hz) and high frequency (HF, 0.56 Hz) with eyes open (EO) and closed (EC). Additional conditions were reading a text fixed to platform (EO-TP) and reading a text stationary on ground (EO-TG). Peak-to-peak (PP) displacement amplitude and AP position of head and pelvis markers were computed for each of 27 continuous perturbation cycles. The time constant and extent of head and pelvis adaptation and the cross-correlation coefficients between head and pelvis were compared across visual conditions and frequencies. Head and pelvis mean positions in space varied little across conditions and perturbation cycles but the mean head PP displacements changed over time. On average, at LF, the PP displacement of the head and pelvis increased progressively. Adaptation was rapid or ineffective with EO, but slower with EO-TG, EO-TP, EC. At HF, the head PP displacement amplitude decreased progressively with fast adaptation rates, while the pelvis adaptation was not apparent. The results show that visual tasks can modulate the adaptation rate, highlight the effect of the perturbation frequency on adaptation and provide evidence of priority assigned to pelvis stabilization over visual tasks at HF. The effects of perturbation frequency and optic flow and their interaction with other sensory inputs and cognitive tasks on the adaptation strategies should be investigated in impaired individuals and considered in the design of rehabilitation protocols.

Intense and unpredictable perturbations during gait training improve dynamic balance abilities in chronic hemiparetic individuals: a randomized controlled pilot trial

Background

Previous studies have assessed the effects of perturbation training on balance after stroke. However, the perturbations were either applied while standing or were small in amplitude during gait, which is not representative of the most common fall conditions. The perturbations were also combined with other challenges such as progressive increases in treadmill speed.

Objective

To determine the benefit of treadmill training with intense and unpredictable perturbations compared to treadmill walking-only training for dynamic balance and gait post-stroke.

Methods

Twenty-one individuals post-stroke with reduced dynamic balance abilities, with or without a history of fall and ability to walk on a treadmill without external support or a walking aid for at least 1 min were allocated to either an unpredictable gait perturbation (Perturb) group or a walking-only (NonPerturb) group through covariate adaptive randomization. Nine training sessions were conducted over 3 weeks. NonPerturb participants only walked on the treadmill but were offered perturbation training after the control intervention. Pre- and post-training evaluations included balance and gait abilities, maximal knee strength, balance confidence and community integration. Six-week phone follow-ups were conducted for balance confidence and community integration. Satisfaction with perturbation training was also assessed.

Results

With no baseline differences between groups (p > 0.075), perturbation training yielded large improvements in most variables in the Perturb (p < 0.05, Effect Size: ES > .46) group (n = 10) and the NonPerturb (p ≤ .089, ES > .45) group (n = 7 post-crossing), except for maximal strength (p > .23) in the NonPerturb group. Walking-only training in the NonPerturb group (n = 8, pre-crossing) mostly had no effect (p > .292, ES < .26), except on balance confidence (p = .063, ES = .46). The effects of the gait training were still present on balance confidence and community integration at follow-up. Satisfaction with the training program was high.

Conclusion

Intense and unpredictable gait perturbations have the potential to be an efficient component of training to improve balance abilities and community integration in individuals with chronic stroke. Retrospective registration: ClinicalTrials.gov. March 18th, 2020. Identifier: NCT04314830.

Effect of Reactive Balance Training Involving Repeated Slips and Trips on Balance Recovery Among Older Adults: A Blinded Randomized Controlled Trial

BACKGROUND

This study examined whether reactive balance training (exposures to slips and trips) could improve balance recovery and reduce perturbation-induced falls among older adults.

METHODS

Forty-four community-dwelling older adults participated in a parallel, blinded randomized controlled trial conducted in a research institute in Sydney, Australia in 2017-2018 (ACTRN12617000564358). The intervention group (n = 22) underwent three 40 minutes sessions (total 120 minutes) that exposed them to (1) 20 trips, (2) 20 slips, and (3) 10 trips and 10 slips in mixed order, over 2 days. The control group (n = 22) received one 40 minutes session of sham training. The primary outcome was falls (>30% body weight in harness) when exposed to trips and slips at post-assessment.

RESULTS

At post-assessment, a total of 51 falls (23 and 27 falls from induced slips and trips, respectively) were recorded in the laboratory. Relative to the control group, the intervention group experienced fewer total falls (rate ratio [RR] = 0.40, 95% confidence interval [CI] = 0.22-0.76), slip falls (RR = 0.33, 95% CI = 0.12-0.90) and trip falls (RR = 0.49, 95% CI = 0.21-1.12). Eight participants reported adverse events (5 in the intervention group and 3 in the control group) which were related mainly to discomfort caused by a suboptimal harness used in the initial stages of the trial.

CONCLUSIONS

The reactive balance training reduced perturbation-induced falls by 60% indicating improved balance recovery from trips and slips. A comfortable safety harness system is essential to prevent discomfort. Reactive balance training may complement traditional exercise programs in fall prevention interventions.

Perturbation-based gait training to improve daily life gait stability in older adults at risk of falling: protocol for the REACT randomized controlled trial

Background

The European population is rapidly ageing. There is an urgent need for innovative solutions to reduce fall risk in older adults. Perturbation-based gait training is a promising new method to improve reactive balance responses. Whereas positive effects on task-specific dynamic balance recovery during gait have been shown in clinical or laboratory settings, translation of these effects to daily life gait function and fall risk is limited. We aim to evaluate the effect of a 4-week perturbation-based treadmill training on daily-life dynamic gait stability, assessed with inertial sensor data. Secondary outcomes are balance recovery performance, clinical balance and gait assessment scores, the amount of physical activity in daily life and falls incidence during 6 months follow-up.

Methods

The study is a monocenter assessor-blinded randomized controlled trial. The target study sample consists of 70 older adults of 65 years and older, living in the community and with an elevated risk of falling. A block-randomization to avoid seasonal effects will be used to allocate the participants into two groups. The experimental group receives a 4-week, two times per week perturbation-based gait training programme on a treadmill, with simulated slips and trips, in combination with cognitive dual tasks. The control group receives a 4-week, two times per week treadmill training programme under cognitive dual-task conditions without perturbations. Participants will be assessed at baseline and after the 4-weeks intervention period on their daily-life gait stability by wearing an inertial sensor on the lower back for seven consecutive days. In addition, clinical balance and gait assessments as well as questionnaires on falls- and gait-efficacy will be taken. Daily life falls will be followed up over 6 months by a fall calendar.

Discussion

Whereas perturbation-based training has shown positive effects in improving balance recovery strategies and in reducing laboratory falls, this study will contribute to investigate the translation of perturbation-based treadmill training effects in a clinical setting towards improving daily life gait stability and reducing fall risk and falls.

Trial registration

NTR7703 / NL66322.028.18, Registered: January 8, 2019; Enrolment of the first participant April 8, 2019.

Transfer and retention effects of gait training with anterior-posterior perturbations to postural responses after medio-lateral gait perturbations in older adults

BACKGROUND

Gait perturbations, occurring in any direction in daily life, may result in a fall. In fall prevention, gait perturbation training is a promising approach. Treadmill perturbations in anterior-posterior direction can easily be applied by accelerations or decelerations of the belt, but it is unknown whether training effects transfer to reactive recovery in medio-lateral direction. We aimed to evaluate the transfer and retention effects of gait training with treadmill perturbations in anterior-posterior direction to medio-lateral reactive recovery.

METHODS

30 community dwelling older adults (>65 years) participated in this study. They were randomly assigned to a treadmill training session either with 16 anterior-posterior perturbations or with treadmill walking. The assessments contained a walking trial with 4 anterior-posterior and 4 medio-lateral perturbations. Deviations in trunk velocity from unperturbed walking were summed over the first three strides after perturbation as a measure of recovery.

FINDINGS

An exposure to gait perturbations during the baseline assessment led to significant improvement of recovery responses. For anterior-posterior perturbations, both groups showed better recovery immediately and 1-week post-intervention, and no group x time interaction was found.. For medio-lateral perturbations, both groups showed better recovery immediately and 1-week post-intervention, and again no group × time interaction.

INTERPRETATION

Baseline assessment with perturbations in anterior-posterior and medio-lateral directions caused significant improvements that were retained. Short-term training can be effective in dynamic stabilization of one's trunk, but our findings do not exclude that multi-directional perturbations may be needed.

Perturbation-Based Balance Training in Postoperative Individuals With Degenerative Cervical Myelopathy

Degenerative cervical myelopathy (DCM) is a common aging condition caused by spinal cord compression. Individuals with DCM often presented with residual balance and functional impairments postoperatively. Perturbation-based balance training (PBT) has been shown to have positive effects on populations with neurological disorders but has yet to be investigated in DCM. The objective of this study was therefore to evaluate the effects of PBT on balance and functional performance in postoperative individuals with DCM. Fifteen postoperative individuals with DCM (DCM group) and 14 healthy adults (healthy control group) were recruited. The DCM group received a 4-weeks PBT using a perturbation treadmill. The outcome measures included mean velocity of center of pressure (COP) during quiet standing; center of mass (COM) variance and reaction time to balance perturbation during standing with forward and backward perturbation; gait speed during level ground walking; Timed Up and Go Test (TUG) and disability questionnaire scores including Visual Analog Scale, Neck Disability Index, and Lower Extremity Function of Japanese Orthopaedic Association Cervical Myelopathy Evaluation Questionnaire. The assessments were conducted pre- and post-training postoperatively for the DCM group but only once for the healthy control group. Significant improvements were observed in the mean velocity of COP, COM variance, reaction time, gait speed, and TUG in the DCM group. Disability questionnaire scores were not significantly different after training in DCM group. For between-group comparisons, significant differences that were observed pre-training were not observed post-training. The 4-weeks PBT is a potential rehabilitation strategy for addressing balance and functional impairment in postoperative individuals with DCM. In addition, the post-training performance in the DCM group exhibited trends comparable to those of age-matched healthy controls. Furthermore, the training regimens offer a practical reference for future studies on populations with balance disorders. Future studies complemented with neurophysiological assessments could reveal more information of the underlying mechanisms of PBT.

Surface Perturbation Training to Prevent Falls in Older Adults: A Highly Pragmatic, Randomized Controlled Trial

BACKGROUND

Falls are the leading cause of injuries among older adults, and trips and slips are major contributors to falls.

OBJECTIVE

The authors sought to compare the effectiveness of adding a component of surface perturbation training to usual gait/balance training for reducing falls and fall-related injury in high-risk older adults referred to physical therapy.

DESIGN

This was a multi-center, pragmatic, randomized, comparative effectiveness trial.

SETTING

Treatment took place within 8 outpatient physical therapy clinics.

PATIENTS

This study included 506 patients 65+ years of age at high fall risk referred for gait/balance training.

INTERVENTION

This trial evaluated surface perturbation treadmill training integrated into usual multimodal exercise-based balance training at the therapist's discretion versus usual multimodal exercise-based balance training alone.

MEASUREMENTS

Falls and injurious falls were assessed with a prospective daily fall diary, which was reviewed via telephone interview every 3 months for 1 year.A total of 211/253 (83%) patients randomized to perturbation training and 210/253 (83%) randomized to usual treatment provided data at 3-month follow-up. At 3 months, the perturbation training group had a significantly reduced chance of fall-related injury (5.7% versus 13.3%; relative risk 0.43) but no significant reduction in the risk of any fall (28% versus 37%, relative risk 0.78) compared with usual treatment. Time to first injurious fall showed reduced hazard in the first 3 months but no significant reduction when viewed over the entire first year.

LIMITATIONS

The limitations of this trial included lack of blinding and variable application of interventions across patients based on pragmatic study design.

CONCLUSION

The addition of some surface perturbation training to usual physical therapy significantly reduced injurious falls up to 3 months posttreatment. Further study is warranted to determine the optimal frequency, dose, progression, and duration of surface perturbation aimed at training postural responses for this population.

Electrocortical activity changes in response to unpredictable trip perturbations induced by a split-belt treadmill

This study explored the contributions of cortical activity in the primary sensorimotor cortex (SMC) and the posterior parietal cortex (PPC) to recovery responses following unpredictable trip perturbations. A technology platform equipped with a programmable split-belt treadmill induced unpredictable trip perturbations while walking. 128-channel non-invasive electroencephalography (EEG) signals were collected. Power spectral analysis was performed to quantify the electrocortical activity of two clusters in the SMC and PPC during quiet standing, steady state walking, and recovery periods. Alpha (8-13 Hz) power of the SMC and PPC was significantly suppressed during the recovery period compared to the standing and walking periods. The main finding of this study could inform the future development gait perturbation paradigms that facilitate the recovery responses in different populations, based on motor learning by repetition.

Human Balance in Response to Continuous, Predictable Translations of the Support Base: Integration of Sensory Information, Adaptation to Perturbations, and the Effect of Age, Neuropathy and Parkinson’s Disease

This short narrative review article moves from early papers that described the behaviour of healthy subjects balancing on a motorized platform continuously translating in the antero-posterior direction. Research from the laboratories of two of the authors and related investigations on dynamic balancing behaviour are briefly summarized. More recent findings challenging time-honoured views are considered, such as the statement that vision plays a head-in-space stabilizing role. The time interval to integrate vision or its withdrawal in the balancing pattern is mentioned as well. Similarities and differences between ageing subjects and patients with peripheral or central disorders are concisely reported. The muscle activities recorded during the translation cycles suggest that vision and amplitude changes of the anticipatory postural activities play a predominant role in controlling dynamic balance during prolonged administration of the predictable perturbation. The potential of this paradigm for rehabilitation of balance problems is discussed.

Older adults demonstrate interlimb transfer of reactive gait adaptations to repeated unpredictable gait perturbations

The ability to rapidly adjust gait to cope with unexpected mechanical perturbations declines with ageing. Previous studies, however, have not ensured that gait stability pre-perturbation was equivalent across participants or age groups which may have influenced the outcomes. In this study, we investigate if age-related differences in stability following gait perturbations remain when all participants walk with equivalent stability. We also examine if interlimb transfer of gait adaptations are observed in healthy older adults, by examining if adaptation to repeated perturbations of one leg can benefit stability recovery when the other leg is perturbed. During walking at their stability-normalised walking speeds (young: 1.32 ± 0.07 m/s; older: 1.31 ± 0.13 m/s; normalised to an average margin of stability of 0.05 m), 30 young and 28 older healthy adults experienced ten unpredictable treadmill belt accelerations (the first and last applied to the right leg, the others to the left leg). Using kinematic data, we assessed the margins of stability during unperturbed walking and the first eight post-perturbation recovery steps. Older adults required three more steps to recover during the first perturbation to each leg than the young adults. Yet, after repeated perturbations of the left leg, older adults required only one more step to recover. Interestingly, for the untrained right leg, the older adults could regain stability with three fewer steps, indicating interlimb transfer of the improvements. Age differences in reactive gait stability remain even when participants’ walk with equivalent stability. Furthermore, we show that healthy older adults can transfer improvements in balance recovery made during repeated perturbations to one limb to their recovery following a perturbation to the untrained limb.

Improvements in balance reaction impairments following reactive balance training in individuals with sub-acute stroke: A prospective cohort study with historical control

Background: Reactive balance training (RBT) has been previously found to reduce fall risk in individuals with sub-acute stroke; however, our understanding of the effects of RBT on specific balance impairments is lacking.Objective: To quantify changes in common balance reaction impairments in individuals with sub-acute stroke resulting from RBT, relative to traditional balance training, using a prospective cohort study design with a historical control group.Methods: Individuals with sub-acute stroke completed either RBT or traditional balance training as part of their routine care during physiotherapy in inpatient rehabilitation. Reactive balance control was assessed using lean-and-release perturbations pre-intervention, post-intervention, and 6-months post-intervention (follow-up). Individuals with impaired balance reactions (delayed foot-off times, slide steps, and/or a preference for stepping with the preferred limb) at the pre-intervention assessment were identified using video and force plate data. Outcome measures (foot-off times, frequency of trials with slide steps, and stepping with the preferred limb) from the RBT participants with impaired reactions were compared for each of the three assessments to the mean values for the participants with impaired reactions in the historical control group.Results: Improvements were observed in all outcome measures for the RBT participants between pre-intervention and post-intervention, and/or between post-intervention and follow-up. These improvements were generally equivalent to, if not better than, the improvements demonstrated by the historical control group.Conclusions: Findings further support the use of RBT for post-stroke inpatient rehabilitation, and provide insight into specific balance reaction impairments that are improved by RBT.

A novel wearable device to deliver unconstrained, unpredictable slip perturbations during gait

Background

Task-specific perturbation training is a widely studied means of fall prevention, utilizing techniques that induce slips or slip-like perturbations during gait. Though effective, these methods only simulate narrow ranges within the larger space of possible slipping conditions encountered in daily life. Here we describe and test a novel, wearable apparatus designed to address these limitations and simulate a diverse range of slipping disturbances.

Methods

The device consists of wireless triggering and detachable outsole components that provide adequate friction with the floor when secured to the wearer’s foot, but suddenly create a low-friction surface underfoot upon release. “Benchtop” tests were carried out to quantify device triggering characteristics (i.e. cutting temperature, release delay) and the resulting friction reduction. The device was also tested on six healthy young adults (3 female, age 23 ± 2.4 years), who walked with and without the device to observe how gait kinematics and spatiotemporal parameters were influenced, then performed 12 walking trials ending with a slip delivered by the device. Each participant also completed a survey to obtain opinions on device safety, device comfort, slip realism, and slip difficulty. A linear mixed effects analysis was employed to compare subject spatiotemporal parameters with and without the apparatus, as well as correlation coefficients and root mean square errors (RMSE) to assess the impact of the device on lower limb gait kinematics. Slip onset phases, distances, directions, velocities, and recovery step locations were also calculated.

Results

This device rapidly diminishes available friction from static coefficients of 0.48 to 0.07, albeit after a substantial delay (0.482 ± 0.181 s) between signal reception and outsole release. Strong correlations (R > 0.93) and small RMSE between gait kinematics with and without the device indicate minimal effects on natural gait patterns, however some spatiotemporal parameters were significantly impacted. A diverse range of slip perturbations and recovery steps were successfully elicited by the device.

Conclusions

Our results highlight the efficacy and utility of a wearable slipping device to deliver diverse slip conditions. Such an apparatus enables the study of unconstrained slips administered across the gait cycle, as well as during different locomotor behaviors like turning, negotiating slopes, and level changes.

Reactive gait and postural adjustments following the first exposures to (un)expected stepdown

This study evaluated the reactive biomechanical strategies associated with both upper- and lower-body (lead and trail limbs) following the first exposures to (un)expected stepdown at comfortable (1.22 ± 0.08 m/s) and fast (1.71 ± 0.11 m/s) walking velocities. Eleven healthy adults completed 34 trails per walking velocity over an 8-m, custom-built track with two forceplates embedded in its center. For the expected stepdown, the track was lowered by 0-, -10- and -20-cm from the site of the second forceplate, whereas the unexpected stepdown was created by camouflaging the second forceplate (-10-cm). Two-way repeated-measurement ANOVAs detected no velocity-related effects of stepdown on kinematic and kinetic parameters during lead limb stance-phase, and on the trail limb stepping kinematics. However, analyses of significant interactions revealed greater peak flexion angles across the trunk and the trail limb joints (hip, knee and ankle) in unexpected versus expected stepdown conditions at a faster walking velocity. The -10-cm unexpected stepdown (main effect) had a greater influence on locomotor behavior compared to expected conditions due mainly to the absence of predictive adjustments, reflected by a significant decrease in peak knee flexion, contact time and vertical impulse during stance-phase. Walking faster (main effect) was associated with an increase in hip peak flexion and net anteroposterior impulse, and a decrease in contact time and vertical impulse during stepdown. The trail limb, in response, swung forward faster, generating a larger and faster recovery step. However, such reactive stepping following unexpected stepdown was yet a sparse compensation for an unstable body configuration, assessed by significantly smaller step width and anteroposterior margin-of-stability at foot-contact in the first-recovery-step compared with expected conditions. These findings depict the impact of the expectedness of stepdown onset on modulation of global dynamic postural control for a successful accommodation of (un)expected surface elevation changes in young, healthy adults.

A survey of Canadian healthcare professionals' practices regarding reactive balance training

Background: Perturbation-based balance training (PBT) is a relatively new type of balance training that aims to improve control of reactions to a loss of balance. This study aimed to determine the prevalence of use of PBT in clinical practice, and the most significant barriers and facilitators to implementing PBT in practice.Methods: Health-care professionals across Canada (primarily physiotherapists and kinesiologists) who provide balance training to individuals with balance impairments and/or increased fall risk completed a questionnaire that asked about knowledge and use of PBT in practice.Results: Overall, 76.3% of participants (299/392) reported that they had used PBT in their practices, with 22.4% (88/392) reporting regular PBT use. Lack of knowledge of PBT appeared to be the most significant barrier for those not currently using PBT in their practices, whereas individuals who were familiar with PBT and open to using it in practice experienced barriers related to training, knowledge, human resources, client characteristics, and the practice setting. More than 90% of respondents were interested in learning more about almost all aspects of PBT.Conclusions: These findings could be used to inform development of future educational strategies to increase uptake of PBT in rehabilitation practice.

A pilot study of reactive balance training using trips and slips with increasing unpredictability in young and older adults: Biomechanical mechanisms, falls and clinical feasibility

BACKGROUND

Exposure to unpredictable trips and slips can improve balance recovery responses but it was not known if older adults can tolerate such high intensity training. The study aim was to determine if reactive balance in both young and older adults could be trained in a single day through exposure to slip and trip hazards hidden in unpredictable walkway locations.

METHODS

Ten young (20-40 yr) and ten older adults (65 + yr) completed 32 trials on a 10-meter trip and slip walkway; 14 slip trials, 14 trip trials and 4 no-perturbation trials presented in a pseudo-random order. Participant usual gait speed was regulated using a metronome and stepping tiles at fixed distances. Gait kinematics (Vicon motion capture), falls (> 30% body weight into the harness), anxiety and confidence to avoid falling were assessed.

FINDINGS

Margin of stability for balance recovery after slips substantially improved at training completion for older adults (effect size = 1.13, P = 0.019). Falls from slips also decreased: 44.4% to 0% in the young adults; and 28.6% to 14.3% in the older adults. Although confidence to avoid falling did not change, anxiety increased during training with one young and three older participants withdrawing during training.

INTERPRETATIONS

The findings indicate exposure to unpredictable perturbations improves reactive balance in young and older adults. However, improvements of balance recovery from trips were not significant. Elevated anxiety levels and a high dropout rate suggest the need for more individualised training over multiple days.

The Body's Compensatory Responses to Unpredictable Trip and Slip Perturbations Induced by a Programmable Split-Belt Treadmill

This paper investigates the influence of two types of gait perturbation (i.e., trip and slip) induced by a programmable split-belt treadmill on the body's compensatory responses. Our fall-inducing technology equipped with a commercially available programmable split-belt treadmill provides unpredictable trip and slip perturbations during walking. Two force plates beneath the split-belt treadmill and a motion capture system quantify the body's kinetic and kinematic behaviors, and a wireless surface electromyography (EMG) system evaluates the lower limb muscle activity. Twenty healthy young adults participated. The perturbations (i.e., trip and slip) were applied randomly to the participant's left foot between the 31st and 40th steps. The kinetic and kinematic behaviors and lower limb muscle activity were assessed during the standing, walking, and recovery periods. Compared with trip perturbations, stepping responses to slip perturbations were quicker and trunk, shoulder, and whole body center of mass movements after slip perturbations were higher; the EMG results showed that tibialis anterior, gastrocnemius, rectus femoris, and biceps femoris activities were also higher. The two common types of gait perturbation (i.e., trip and slip) induced by a commercially available programmable split-belt treadmill influenced the body's compensatory responses.

The effect of the most common gait perturbations on the compensatory limb's ankle, knee, and hip moments during the first stepping response

BACKGROUND

Trips and slips, the two most common gait perturbations, often cause falls. Multiple studies have focused mainly on the kinematics of multiple body segments in response to an unexpected trip or slip induced by mechanical obstacles, cables, treadmills, and slippery agents or contaminants on a floor. Few studies have examined the joint moments of the compensatory limb following an unexpected trip on an obstacle.

RESEARCH QUESTION

This proof-of-concept study sought to assess the ankle, knee, and hip moments of the compensatory limb during normal walking and the first stepping response following the two most common gait perturbations.

METHODS

Eighteen healthy young adults completed 4 trials (2 trials with a random trip perturbation and 2 trials with a random slip perturbation) while walking on a split-belt treadmill. In each trial, the motorized treadmill induced either an unexpected trip or slip perturbation to the left foot between the 31 st and 40th step randomly. A motion capture system recorded the positions of body segments, the joint moments (i.e., ankle, knee, and hip moments) of the compensatory limb were quantified, and the maximum joint moments were assessed during normal walking and the first stepping response.

RESULTS

Compensatory limb's ankle plantarflexion, knee flexion, hip flexion, and hip extension moments were significantly higher for a slip perturbation than for a trip perturbation during the first stepping response. Compensatory limb's knee flexion, hip flexion, and hip extension moments were also significantly higher during the first stepping response to a slip perturbation compared to normal walking.

SIGNIFICANCE

This proof-of-concept study is the first to investigate the ankle, knee, and hip moments of the compensatory limb during the first stepping response following unexpected gait perturbations induced by a split-belt treadmill. The findings are expected to improve the gait perturbation paradigms developed for training balance-impaired individuals.

Fear of Falling Contributing to Cautious Gait Pattern in Women Exposed to a Fictional Disturbing Factor: A Non-randomized Clinical Trial

Objective: This study aimed to investigate the gait pattern of elderly women with and without fall-history, with high and low fear of falling, when exposed to a disturbing factor. Materials and Methods: Forty-nine elderly women without cognitive impairment agreed to participate. Participants were divided into four groups, considering the history of falls and fear of falling. Three-dimensional gait analysis was performed to assess gait kinematics before and after exposure to the fictional disturbing factor (psychological and non-motor agent). Results: After being exposed to the perturbation, all showed shorter step length, stride length and slower walking speed. Those without fall-history and with high fear of falling showed greater changes and lower Gait Profile Score. Conclusion: The gait changes shown in the presence of a fear-of-falling causing agent led to a cautious gait pattern in an attempt to increase protection. However, those changes increased fall-risk, boosted by fear of falling. Clinical Trial Registration: www.residentialclinics.gov.br, identifier: RBR-35xhj5.

Effects of Pulmonary Rehabilitation on Gait Characteristics in Patients with COPD

Pulmonary rehabilitation (PR) improves lower-limb muscle function in patients with chronic obstructive pulmonary disease (COPD). However, it remains unclear whether patients improve gait characteristics, in particular stride-to-stride fluctuations that are associated with fall risks. This study aims to identify whether, and to what extent, PR affects positively gait characteristics in COPD. In this prospective observational study, 44 COPD patients (aged: 62 ± 7 years; Forced expiratory volume in 1 s 56 ± 20% predicted) performed self-paced, treadmill 6-min-walk tests (Gait Real-time Analysis Interactive Lab) before and after PR, while spatiotemporal parameters and center of mass position were recorded (100 Hz, Vicon Nexus). Standard deviation, coefficient of variation, predictability (sample entropy), and consistency in organization (local divergence exponent) were calculated. Sub-analysis was performed to identify gait differences between good and poor responders (<30 m change in a 6-min-walk distance). Patients demonstrated shorter stride times (p = 0.001) and improved lower-limb muscle function (p < 0.001) following PR. The good responders had a greater increase in stride length (p < 0.001) and a greater decrease in stride time (p < 0.001) compared to the poor responders. Current PR improved stride time in patients, while movement patterns within stride-to-stride fluctuations did not change. Training programs specifically targeting balance issues and gait function may be beneficial in improving gait characteristics in COPD.

The Effect of Active Physical Training Interventions on Reactive Postural Responses in Older Adults: A Systematic Review

BACKGROUND

A variety of physical interventions have been used to improve reactive balance in older adults.

PURPOSE

To summarize the effectiveness of active treatment approaches to improve reactive postural responses in community-dwelling older adults.

DESIGN

Systematic review guided by PRISMA guidelines.

STUDY SELECTION

A literature search included the databases PubMed, OVID, CINAHL, ClinicalTrials.gov, OTseeker, and PEDro up to December 2017. Randomized controlled trials that evaluated quantitative measures of reactive postural responses in healthy adults following participation in an active physical training program were included.

DATA SYNTHESIS

Of 4,481 studies initially identified, 11 randomized controlled trials covering 313 participants were selected for analysis. Study designs were heterogeneous, preventing a quantitative analysis. Nine of the 11 studies reported improvements in reactive postural responses.

CONCLUSIONS

Several clinically feasible training methods have the potential to improve reactive postural responses in older adults; however, conclusions on the efficacy of treatment methods are limited because of numerous methodological issues and heterogeneity in outcomes and intervention procedures.

Characterizing slip-like responses during gait using an entire support surface perturbation: Comparisons to previously established slip methods

BACKGROUND

The characteristics of experimentally induced slips (low-friction surfaces and non-motorized platforms) in laboratory settings are influenced by participant gait velocity, contact surface area, and level of friction between the foot and surface. However, motorized platforms that could account for these factors during slip-like paradigms have not been extensively used.

RESEARCH QUESTION

How does slip-like perturbations evoked via a motorized platform change gait characteristics and postural stability during overground walking?

METHODS

Ten healthy young adults performed 4 overground, self-paced walking trials, with the 4^th trial including an unexpected forward support surface translation at heel-strike during steady state walking. Kinematic and kinetic data were collected, with step characteristics (time, distance, velocity) and postural stability calculated to compare between normal gait and slip-like trials. Slip foot characteristics were also determined.

RESULTS

Peak slipping foot velocity variability was considerably smaller compared to previously reported low-friction and non-motorized perturbations. The centre of mass was shifted more posteriorly (thus in a less stable location) by the end of the platform acceleration phase compared to the same time point post-heel strike during normal gait trials. Participants successfully responded to every slip-like perturbation by significantly increasing step time, decreasing step distance, and decreasing step velocity.

SIGNIFICANCE

Our results demonstrate the repeatability and consistency of a motorized support surface paradigm to induce slip-like perturbations. Furthermore, stability and step characteristic results confirm posterior shifts in stability and appropriate stepping responses, mimicking how participants would react if responding to a real world slip.

Stability-normalised walking speed: A new approach for human gait perturbation research

In gait stability research, neither self-selected walking speeds, nor the same prescribed walking speed for all participants, guarantee equivalent gait stability among participants. Furthermore, these options may differentially affect the response to different gait perturbations, which is problematic when comparing groups with different capacities. We present a method for decreasing inter-individual differences in gait stability by adjusting walking speed to equivalent margins of stability (MoS). Eighteen healthy adults walked on a split-belt treadmill for two-minute bouts at 0.4 m/s up to 1.8 m/s in 0.2 m/s intervals. The stability-normalised walking speed (MoS = 0.05 m) was calculated using the mean MoS at touchdown of the final 10 steps of each speed. Participants then walked for three minutes at this speed and were subsequently exposed to a treadmill belt acceleration perturbation. A further 12 healthy adults were exposed to the same perturbation while walking at 1.3 m/s: the average of the previous group. Large ranges in MoS were observed during the prescribed speeds (6-10 cm across speeds) and walking speed significantly (P < 0.001) affected MoS. The stability-normalised walking speeds resulted in MoS equal or very close to the desired 0.05 m and reduced between-participant variability in MoS. The second group of participants walking at 1.3 m/s had greater inter-individual variation in MoS during both unperturbed and perturbed walking compared to 12 sex, height and leg length-matched participants from the stability-normalised walking speed group. The current method decreases inter-individual differences in gait stability which may benefit gait perturbation and stability research, in particular studies on populations with different locomotor capacities. [Preprint: https://doi.org/10.1101/314757].

Effects of Perturbation-Based Balance Training in Subacute Persons With Stroke: A Randomized Controlled Trial

BACKGROUND

Reactive balance responses are critical for fall prevention. Perturbation-based balance training (PBBT) has shown a positive effect in reducing the risk of falls among older adults and persons with Parkinson's disease.

OBJECTIVE

To explore the effect of a short-term PBBT on reactive balance responses, performance-based measures of balance and gait and balance confidence.

METHODS

Thirty-four moderate-high functioning, subacute persons with stroke (PwS) (lower extremity Fugl-Meyer score 29.2 ± 4.3; Berg Balance Scale [BBS] score 43.8 ± 9.5, 42.0 ± 18.7 days after stroke onset) hospitalized in a rehabilitation setting were randomly allocated to PBBT (n = 18) and weight shifting and gait training (WS&GT) (n = 16). Both groups received 12 training sessions, 30 minutes each, for a period of 2.5 weeks. PBBT included unexpected balance perturbations during standing and treadmill walking, WS&GT included weight shifting in standing and treadmill walking without perturbations. The main outcome measures, that is, multiple step-threshold and fall-threshold were examined at baseline, immediately postintervention, and about 5 weeks postintervention. The secondary outcome measures, that is, BBS, 6-minute walk test (6MWT), 10-meter walk test (10MWT), and Activity-specific Balance Confidence (ABC) scale were examined at baseline and immediately postintervention.

RESULTS

Compared with the WS&GT group, immediately postintervention participants in the PBBT group showed higher multiple-step thresholds in response to forward and backward surface translations (effect size [ES] = 1.07 and ES = 1.10, respectively) and moderate ES in the ABC scale (ES = 0.74). No significant differences were found in fall-threshold, BBS, 6MWT, and 10MWT between the groups.

CONCLUSIONS

Inclusion of perturbation training during rehabilitation of PwS improved reactive balance and balance confidence.

Effects of Aging and Task Prioritization on Split-Belt Gait Adaptation

Background: Age-related changes in the sensorimotor system and cognition affect gait adaptation, especially when locomotion is combined with a cognitive task. Performing a dual-task can shift the focus of attention and thus require task prioritization, especially in older adults. To gain a better understanding of the age-related changes in the sensorimotor system, we examined how age and dual-tasking affect adaptive gait and task prioritization while walking on a split-belt treadmill.

Methods: Young (21.5 ± 1.0 years, n = 10) and older adults (67.8 ± 5.8 years, n = 12) walked on a split-belt treadmill with a 2:1 belt speed ratio, with and without a cognitive Auditory Stroop task. Symmetry in step length, limb excursion, and double support time, and strategy variables swing time and swing speed were compared between the tied-belt baseline (BL), early (EA) and late split-belt adaptation (LA), and early tied-belt post-adaptation (EP).

Results: Both age groups adapted to split-belt walking by re-establishing symmetry in step length and double support time. However, young and older adults differed on adaptation strategy. Older vs. young adults increased swing speed of the fast leg more during EA and LA (0.10–0.13 m/s), while young vs. older adults increased swing time of the fast leg more (2%). Dual-tasking affected limb excursion symmetry during EP. Cognitive task performance was 5–6% lower during EA compared to BL and LA in both age groups. Older vs. young adults had a lower cognitive task performance (max. 11% during EA).

Conclusion: Healthy older adults retain the ability to adapt to split-belt perturbations, but interestingly age affects adaptation strategy during split-belt walking. This age-related change in adaptation strategy possibly reflects a need to increase gait stability to prevent falling. The decline in cognitive task performance during early adaptation suggests task prioritization, especially in older adults. Thus, a challenging motor task, like split-belt adaptation, requires prioritization between the motor and cognitive task to prevent adverse outcomes. This suggests that task prioritization and adaptation strategy should be a focus in fall prevention interventions.

Retention, savings and interlimb transfer of reactive gait adaptations in humans following unexpected perturbations

Reactive locomotor adaptations are crucial for safe mobility, but remain relatively unexplored. Here we assess reactive gait adaptations, and their retention, savings and interlimb transfer. Using new methods to normalise walking speed and perturbation magnitude, we expose eighteen healthy adults to ten unexpected treadmill belt accelerations during walking (the first and last perturbing the right leg, the others perturbing the left leg) on two days, one month apart. Analysis of the margins of stability using kinematic data reveals that humans reactively adapt gait, improving stability and taking fewer recovery steps, and fully retain these adaptations over time. On re-exposure, retention and savings lead to further improvements in stability. Currently, the role of interlimb transfer is unclear. Our findings show that humans utilise retention and savings in reactive gait adaptations to benefit stability, but that interlimb transfer may not be exclusively responsible for improvements following perturbations to the untrained limb.