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Wearable sensors are increasingly popular in concussion research because of their objective quantification of subtle balance deficits. However, normative data and minimal detectable change (MDC) values are necessary to serve as references for diagnostic use and tracking longitudinal recovery. To identify normative and MDC values for instrumented static- and reactive-balance tests, an instrumented static mediolateral (ML) root mean square (RMS) sway standing balance assessment and the instrumented, modified push and release (I-mP&R), respectively. Cross-sectional study. Clinical setting. Normative static ML RMS sway and I-mP&R data were collected on 377 (n = 184 female) healthy National Collegiate Athletic Association Division I athletes at the beginning of their competitive seasons. Test-retest data were collected in 36 healthy control athletes based on standard recovery timelines after concussion. Descriptive statistics, intraclass correlation coefficients (ICCs), and MDC values were calculated for primary outcomes of ML RMS sway in a static double-limb stance on firm ground and a foam block, and time to stability and latency from the I-mP&R in single- and dual-task conditions. Normative outcomes across static ML RMS sway and I-mP&R were sensitive to sex and type of footwear. Mediolateral RMS sway demonstrated moderate reliability in the firm condition (ICC = 0.73; MDC = 2.7 cm/s2) but poor reliability in the foam condition (ICC = 0.43; MDC = 11.1 cm/s2). Single- and dual-task times to stability from the I-mP&R exhibited good reliability (ICC = 0.84 and 0.80, respectively; MDC = 0.25 and 0.29 seconds, respectively). Latency from the I-mP&R had poor to moderate reliability (ICC = 0.38 and 0.55; MDC = 107 and 105 milliseconds). Sex-matched references should be used for instrumented static- and reactive-balance assessments. Footwear may explain variability in static ML RMS sway and time to stability of the I-mP&R. Moderate-to-good reliability suggests time to stability from the I-mP&R and ML RMS static sway on firm ground can be used for longitudinal assessments. [ABSTRACT FROM AUTHOR]

This systematic review examined available findings on spatial and temporal characteristics of cortical activity in response to unpredicted mechanical perturbations. Secondly, this review investigated associations between cortical activity and behavioral/biomechanical measures. Databases were searched from 1980–2021 and a total of 35 cross-sectional studies (31 EEG and 4 fNIRS) were included. Majority of EEG studies assessed perturbation-evoked potentials (PEPs), whereas other studies assessed changes in cortical frequencies. Further, fNIRS studies assessed hemodynamic changes. The PEP-N1, commonly identified at sensorimotor areas, was most examined and was influenced by context prediction, perturbation magnitude, motor adaptation and age. Other PEPs were identified at frontal, parietal and sensorimotor areas and were influenced by task position. Further, changes in cortical frequencies were observed at prefrontal, sensorimotor and parietal areas and were influenced by task difficulty. Lastly, hemodynamic changes were observed at prefrontal and frontal areas and were influenced by task prediction. Limited studies reported associations between cortical and behavioral outcomes. This review provided evidence regarding the involvement of cerebral cortex for sensory processing of unpredicted perturbations, error-detection of expected versus actual postural state, and planning and execution of compensatory stepping responses. There is still limited evidence examining cortical activity during reactive balance tasks in populations with high fall-risk. [ABSTRACT FROM AUTHOR]

BackgroundEffective training of the backward step response could be beneficial to improve postural stability and prevent falls. Unpredicted perturbation-based balance training (PBT), widely known as compensatory-step training, may enhance the fear of falling and the patterns of postural muscle co-contraction. Contrastingly, PBT with predictable direction or both direction and timing would suppress the fear and the co-contraction patterns during training, but the efficacy of predictable PBT for unpredictable perturbations is still unknown.ObjectiveTo compare the adaptation effects of compensatory-step training with and without predictable perturbations on backward stepping against unpredictable perturbations.MethodsThirty-three healthy young adults were randomly assigned to one of the following step training groups: Unpredicted, Predicted, and Self-initiated. In training sessions, participants were perturbed to induce a compensatory step with (Predicted group) or without (Unpredicted group) knowledge of the perturbation’s direction or while knowing both the direction and timing of the perturbation (Self-initiated group). In test sessions (pre- and post-training), participants were instructed to recover their postural stability in response to an unpredicted perturbation. The margin of stability (MOS), center of mass (COM) shift, and step characteristics were measured during a backward step in both test and training sessions.ResultsAll three groups showed a significant increase in the step length and velocity in the post-training sessions compared to those in the pre-training sessions. Moreover, in the Unpredicted and Predicted groups, but not in the Self-initiated group, the MOS at step contact was significantly increased following the training session. In addition, the Self-initiated group showed a significant increase in COM shift at 50 ms after slip onset during training compared to the Unpredicted and Predicted groups.ConclusionUnpredicted and predicted PBT improve step characteristics during backward stepping against unpredictable perturbations. Moreover, the unpredictable PBT and PBT with direction-predictable perturbations enhance the feedback postural control reflected as the postural stability at step contact.

Background: Effective training of the backward step response could be beneficial to improve postural stability and prevent falls. Unpredicted perturbation-based balance training (PBT), widely known as compensatory-step training, may enhance the fear of falling and the patterns of postural muscle co-contraction. Contrastingly, PBT with predictable direction or both direction and timing would suppress the fear and the co-contraction patterns during training, but the efficacy of predictable PBT for unpredictable perturbations is still unknown. Objective: To compare the adaptation effects of compensatory-step training with and without predictable perturbations on backward stepping against unpredictable perturbations. Methods: Thirty-three healthy young adults were randomly assigned to one of the following step training groups: Unpredicted, Predicted, and Self-initiated. In training sessions, participants were perturbed to induce a compensatory step with (Predicted group) or without (Unpredicted group) knowledge of the perturbation's direction or while knowing both the direction and timing of the perturbation (Self-initiated group). In test sessions (pre- and post-training), participants were instructed to recover their postural stability in response to an unpredicted perturbation. The margin of stability (MOS), center of mass (COM) shift, and step characteristics were measured during a backward step in both test and training sessions. Results: All three groups showed a significant increase in the step length and velocity in the post-training sessions compared to those in the pre-training sessions. Moreover, in the Unpredicted and Predicted groups, but not in the Self-initiated group, the MOS at step contact was significantly increased following the training session. In addition, the Self-initiated group showed a significant increase in COM shift at 50 ms after slip onset during training compared to the Unpredicted and Predicted groups. Conclusion: Unpredicted and predicted PBT improve step characteristics during backward stepping against unpredictable perturbations. Moreover, the unpredictable PBT and PBT with direction-predictable perturbations enhance the feedback postural control reflected as the postural stability at step contact. [ABSTRACT FROM AUTHOR]

Background: Deficits in neuromuscular control are widely reported after mild traumatic brain injury (mTBI). These deficits are speculated to contribute to the increased rate of musculoskeletal injuries after mTBI. However, a concrete mechanistic connection between post-mTBI deficits and musculoskeletal injuries has yet to be established. While impairments in some domains of balance control have been linked to musculoskeletal injuries, reactive balance control has received little attention in the mTBI literature, despite the inherent demand of balance recovery in athletics. Our central hypothesis is that the high rate of musculoskeletal injuries after mTBI is in part due to impaired reactive balance control necessary for balance recovery. The purpose of this study is to (1) characterize reactive postural responses to recover balance in athletes with recent mTBI compared to healthy control subjects, (2) determine the extent to which reactive postural responses remain impaired in athletes with recent mTBI who have been cleared to return to play, and (3) determine the relationship between reactive postural responses and acute lower extremity musculoskeletal injuries in a general sample of healthy collegiate athletes.Methods: This two-phase study will take place at the University of Utah in coordination with the University of Utah Athletics Department. Phase 1 will evaluate student-athletes who have sustained mTBI and teammate-matched controls who meet all the inclusion criteria. The participants will be assessed at multiple time points along the return-to-play progress of the athlete with mTBI. The primary outcome will be measures of reactive postural response derived from wearable sensors during the Push and Release (P&R) test. In phase 2, student-athletes will undergo a baseline assessment of postural responses. Acute lower extremity musculoskeletal injuries for each participant will be prospectively tracked for 1 year from the date of first team activity. The primary outcomes will be the measures of reactive postural responses and the time from first team activity to lower extremity injury.Discussion: Results from this study will further our understanding of changes in balance control, across all domains, after mTBI and identify the extent to which postural responses can be used to assess injury risk in collegiate athletes.

Key points: It is unclear whether the visual input that accompanies a perturbation of a standing person can affect whether a recovery step is taken.Visual motion speeds were manipulated during unexpected forward and backward shoulder pulls.Visual motion that appeared slower than actual body motion reduced the initial in‐place resistance to the perturbation.As a result of the modulation of the in‐place response, less pull force was needed to trigger a step when visual velocity appeared slower than normal.The visuomotor postural response occurred earlier and was larger when the full‐field visual input was paired with a mechanical perturbation. The present study aimed to determine how visual motion evoked by an upper body perturbation during standing affects compensatory postural responses. This was investigated by rotating the visual field forwards or backwards about the ankle, time‐locked to a forwards or backwards shoulder pull. Kinematic, kinetic and electromyographic responses were recorded to a range of pull forces over 160 trials in 12 healthy adults (mean ± SD = 31 ± 5.8 years). Stepping threshold forces and in‐place postural responses were compared between conditions. When the visual field moved in the same direction as the pull, so that the apparent velocity of the body was reduced (SLOW condition), the pull‐force required to induce a step was less than when the visual field either rotated in the opposite direction (FAST) or was unaltered (NATURAL). For in‐place responses, the body was displaced further in the direction of the pull in the SLOW condition. This was the result of a reduction in the resistive force from lower leg muscles 130 ms after the visual motion onset. In trials with no pull, the visual motion induced postural responses that were later (290 ms) and had smaller amplitudes compared to when visual motion is paired with an unexpected perturbation of the body. The results suggest that the apparent speed of the visual environment during a perturbation does influence whether a compensatory step is taken, not via a direct effect on the decision to step but by modulating the initial in‐place response. Key points: It is unclear whether the visual input that accompanies a perturbation of a standing person can affect whether a recovery step is taken.Visual motion speeds were manipulated during unexpected forward and backward shoulder pulls.Visual motion that appeared slower than actual body motion reduced the initial in‐place resistance to the perturbation.As a result of the modulation of the in‐place response, less pull force was needed to trigger a step when visual velocity appeared slower than normal.The visuomotor postural response occurred earlier and was larger when the full‐field visual input was paired with a mechanical perturbation. [ABSTRACT FROM AUTHOR]

Introduction: Asymmetrical sensorimotor function after stroke creates unique challenges for bipedal tasks such as walking or perturbation-induced reactive stepping. Preference for initiating steps with the less-involved (preferred) leg after a perturbation has been reported with limited information on the stepping response of the more-involved (non-preferred) leg. Understanding the capacity of both legs to respond to a perturbation would enhance the design of future treatment approaches. This pilot study investigated the difference in perturbation-induced stepping between legs in stroke participant and non-impaired controls. We hypothesized that stepping performance will be different between groups as well as between legs for post-stroke participants.Methods: Thirty-six participants (20 persons post-stroke, 16 age matched controls) were given an anterior perturbation from three stance positions: symmetrical (SS), preferred asymmetrical (PAS−70% body weight on the preferred leg), and non-preferred asymmetrical (N-PAS−70% body weight on the non-preferred leg). Kinematic and kinetic data were collected to measure anticipatory postural adjustment (APA), characteristics of the first step (onset, length, height, duration), number of steps, and velocity of the body at heel strike. Group differences were tested using the Mann-Whitney U-test and differences between legs tested using the Wilcoxon signed-rank test with an alpha level of 0.05.Results: Stepping with the more-involved leg increased from 11.5% of trials in SS and N-PAS up to 46% in PAS stance position for participants post-stroke. Post-stroke participants had an earlier APA and always took more steps than controls to regain balance. However, differences between post-stroke and control participants were mainly found when stance position was modified. Compare to controls, steps with the preferred leg (N-PAS) were earlier and shorter (in time and length), whereas steps with the non-preferred leg (PAS) were also shorter but took longer. For post-stroke participants, step duration was longer and utilized more steps when stepping with the more-involved leg compared to the less-involved leg.Conclusions: Stepping with the more-involved leg can be facilitated by unweighting the leg. The differences between groups, and legs in post-stroke participants illustrate the simultaneous bipedal role (support and stepping) both legs have in reactive stepping and should be considered for reactive balance training.

Background: The specific mechanisms responsible for age-related decline in forward stability control remain unclear. Previous work has suggested reactive control of net ground reaction force (GRFnet) eccentricity may be responsible for age-related challenges in mediolateral stability control during the restabilisation phase of forward compensatory stepping responses.Research Questions: Does reactive control of GRFnet eccentricity play a role in managing forward stability control during the restabilisation phase of a forward stepping response to external balance perturbation?Methods: Healthy younger (YA) (n = 20) and older adults (OA) (n = 20) were tethered to a rigid frame, via adjustable cable. Participants were released from a standardised initial forward lean and regained their balance using a single step. Whole-body motion analysis and four force platforms were utilised for data acquisition. Forward instability was quantified as centre of mass (COM) incongruity - the difference between the first local peak and final stable anterior COM positions. The extent of GRFnet eccentricity was quantified as the sagittal-plane angle of divergence of the line of action of the GRFnet relative to the COM. Two discrete points during restabilisation were examined (P1 and P2), which have been suggested to be indicative of proactive and reactive COM control, respectively. Age-related differences in magnitude, timing and trial-to-trial variability of kinematic and kinetic outcome variables were analysed using two-factor ANOVAs with repeated-measures.Results: OA exhibited greater COM incongruity magnitude and variability - both were reduced with trial-repetition. There were no age-related differences in the magnitude or timing of P2. Instead, OA exhibited a reduced magnitude of GRFnet eccentricity at P1. There was a positive correlation between AP COM incongruity magnitude and P1 magnitude.Significance: Different from mediolateral stability control, the present results suggest that OA may experience forward stability control challenges as a function of insufficient preparatory lower limb muscle activation prior to foot-contact. [ABSTRACT FROM AUTHOR]

Introduction: Asymmetrical sensorimotor function after stroke creates unique challenges for bipedal tasks such as walking or perturbation-induced reactive stepping. Preference for initiating steps with the less-involved (preferred) leg after a perturbation has been reported with limited information on the stepping response of the more-involved (non-preferred) leg. Understanding the capacity of both legs to respond to a perturbation would enhance the design of future treatment approaches. This pilot study investigated the difference in perturbation-induced stepping between legs in stroke participant and non-impaired controls. We hypothesized that stepping performance will be different between groups as well as between legs for post-stroke participants. Methods: Thirty-six participants (20 persons post-stroke, 16 age matched controls) were given an anterior perturbation from three stance positions: symmetrical (SS), preferred asymmetrical (PAS−70% body weight on the preferred leg), and non-preferred asymmetrical (N-PAS−70% body weight on the non-preferred leg). Kinematic and kinetic data were collected to measure anticipatory postural adjustment (APA), characteristics of the first step (onset, length, height, duration), number of steps, and velocity of the body at heel strike. Group differences were tested using the Mann-Whitney U -test and differences between legs tested using the Wilcoxon signed-rank test with an alpha level of 0.05. Results: Stepping with the more-involved leg increased from 11.5% of trials in SS and N-PAS up to 46% in PAS stance position for participants post-stroke. Post-stroke participants had an earlier APA and always took more steps than controls to regain balance. However, differences between post-stroke and control participants were mainly found when stance position was modified. Compare to controls, steps with the preferred leg (N-PAS) were earlier and shorter (in time and length), whereas steps with the non-preferred leg (PAS) were also shorter but took longer. For post-stroke participants, step duration was longer and utilized more steps when stepping with the more-involved leg compared to the less-involved leg. Conclusions: Stepping with the more-involved leg can be facilitated by unweighting the leg. The differences between groups, and legs in post-stroke participants illustrate the simultaneous bipedal role (support and stepping) both legs have in reactive stepping and should be considered for reactive balance training. [ABSTRACT FROM AUTHOR]

The ability to respond quickly and accurately to an external perturbation with a stepping response is critical to avoid falls and this ability is impaired in older, compared to young adults. However, little is known about whether young and older adults improve compensatory stepping responses similarly with practice. This study compares the extent to which young and older adults can improve, retain, and generalize postural compensatory steps in response to external perturbations. Centre of mass displacement, step characteristics and lower leg muscle activation latencies were measured during one training session of compensatory stepping in response to large surface translations in 13 young and 12 older adults. Retention was tested 24 hours later. Older adults decreased their centre of mass displacements over repeated exposure to large surface translations in both the anterior and posterior directions and retained these improvements. In contrast, young adults only showed adaptation and retention of forward stepping responses. Neither group was able to generalize improvements in stepping responses across directions. These results suggest step training may be beneficial for older adults, however additional, multidirectional training may be necessary to facilitate generalization of postural stepping responses for any direction of a slip or trip.

Purpose:The purpose of this study is to characterize the base-width neutral step (BNS) as the first step in a compensatory step response in persons with moderate Parkinson's disease (PD), and its effect on balance recovery.Materials and Methods:Ten PD and 10 healthy controls (HCs) responded to a posterior waist pull. A BNS was defined if the first step was less than 50 mm. The length, height, duration and velocity of the BNS and its effect on balance recovery time and center of mass location at recovery were compared to the first step within other stepping strategies (single step (SS), multiple step (MS)). A linear mixed model was used to compare across strategies.Results:Six of ten persons with PD compared to zero HC used a BNS. The BNS was shorter in length and duration compared to MS responses in HC, and shorter in duration compared to MS responses in PD. The BNS was slower in velocity compared to every other strategy. BNS use resulted in a longer recovery time compared to all strategies in HC and SS responses in PD, and trended toward a longer recovery time compared to MS responses in PD.Conclusions:The BNS as the first step in a MS response may be an unreported strategy for compensatory stepping in PD. This study suggests that the cost of utilizing the BNS may be a longer time for recovery, but further work is necessary to understand the progression of the BNS as PD severity increases. [ABSTRACT FROM AUTHOR]

Age-related mediolateral instability during forward stepping reactions evoked by whole-body perturbation is believed to occur independent of the initial temporospatial parameters prior to step-contact. Recent research is beginning to explore the restabilisation phase, following step-contact, as the origin of such instability. This work sought to uncover potential mechanisms underlying age-related mediolateral instability during restabilisation by examining whole-body centre of mass (COM) kinematics and the orientation of the net ground reaction force relative to the COM. Healthy younger ( n =20) and older adults ( n =20) were anchored to a rigid frame, via adjustable cable. After establishing a standardised initial forward lean, cable release occurred with pseudorandom timing. Participants regained their balance using a single self-selected step. The potential for lateral instability was quantified by COM kinematics. The angle of divergence of the line of action of the net ground reaction force relative to the COM was quantified and examined at three discrete points during restabilisation, as indices of COM control. Age-related differences in magnitude and trial-to-trial variability were analysed. Older adults exhibited increased ML COM incongruity and trial-to-trial variability, which were reduced with trial repetition. Older adults required an increased time to reorient the net ground reaction force, which was correlated with the increased lateral COM displacement during restabilisation. The present results support the idea that age-related mediolateral instability occurs during restabilisation and may be linked to the reactive control of the orientation of the net ground reaction force with respect to the centre of mass. [ABSTRACT FROM AUTHOR]

The ability to respond quickly and accurately to an external perturbation with a stepping response is critical to avoid falls and this ability is impaired in older, compared to young adults. However, little is known about whether young and older adults improve compensatory stepping responses similarly with practice. This study compares the extent to which young and older adults can improve, retain, and generalize postural compensatory steps in response to external perturbations. Centre of mass displacement, step characteristics and lower leg muscle activation latencies were measured during one training session of compensatory stepping in response to large surface translations in 13 young and 12 older adults. Retention was tested 24 h later. Older adults decreased their center of mass displacements over repeated exposure to large surface translations in both the anterior and posterior directions and retained these improvements. In contrast, young adults only showed adaptation and retention of forward stepping responses. Neither group was able to generalize improvements in stepping responses across directions. These results suggest step training may be beneficial for older adults, however additional, multidirectional training may be necessary to facilitate generalization of postural stepping responses for any direction of a slip or trip. [ABSTRACT FROM AUTHOR]

The effects of deep brain stimulation (DBS) on balance in people with Parkinson's disease (PD) are not well established. This study examined whether DBS randomized to the subthalamic nucleus (STN; n = 11) or globus pallidus interna (GPi; n = 10) improved compensatory stepping to recover balance after a perturbation. The standing surface translated backward, forcing subjects to take compensatory steps forward. Kinematic and kinetic responses were recorded. PD-DBS subjects were tested off and on their levodopa medication before bilateral DBS surgery and retested 6 mo later off and on DBS, combined with off and on levodopa medication. Responses were compared with PD-control subjects (n 8) tested over the same timescale and 17 healthy control subjects. Neither DBS nor levodopa improved the stepping response. Compensatory stepping in the best-treated state after surgery (DBSDOPA) was similar to the best-treated state before surgery (DOPA) for the PD-GPi group and the PD-control group. For the PD-STN group, there were more lateral weight shifts, a delayed foot-off, and a greater number of steps required to recover balance in DBSDOPA after surgery compared with DOPA before surgery. Within the STN group five subjects who did not fall during the experiment before surgery fell at least once after surgery, whereas the number of falls in the GPi and PD-control groups were unchanged. DBS did not improve the compensatory step response needed to recover from balance perturbations in the GPi group and caused delays in the preparation phase of the step in the STN group. [ABSTRACT FROM AUTHOR]

We aimed to examine the trial-to-trial changes in the reactive balance response to large magnitude slip-like treadmill perturbations in stance and whether the acquired adaptive changes could be appropriately scaled to a higher intensity perturbation. Seventeen young adults experienced 15 slips for training on level I intensity. Pre- and post-training slips were delivered at a higher intensity (20% > level I). Pre- and post-slip onset stability (at liftoff and touchdown of stepping limb) was measured as the shortest distance of the center of mass ( COM) position (XCOM/BOS) and velocity (ẊCOM/BOS) relative to base of support ( BOS) from a predicted threshold for backward loss of balance. The number of steps to recover balance, compensatory step length and peak trunk angle were recorded. The post-slip onset stability (at liftoff and touchdown) significantly increased across the trials with no change in preslip stability. Improvement in stability at touchdown positively correlated with an anterior shift in XCOM/BOS but not with ẊCOM/BOS. Consequently, the number of steps required to recover balance declined. The adaptive change in XCOM/BOS resulted from an increase in compensatory step length and reduced trunk extension. Individuals also improved post-slip onset stability on a higher intensity perturbation post-training compared with the pre-training trial. The results support that the CNS adapts to fixed intensity slip-like perturbations primarily by improving the reactive stability via modulation in compensatory step length and trunk extension. Furthermore, based on prior experience from the training phase, the acquired adaptive response can be successfully calibrated to a higher intensity perturbation. [ABSTRACT FROM AUTHOR]

Highlights: [•] We studied balance recovery in healthy controls (HC) vs. patients with moderate PD. [•] Goal was to determine how parameters change in moderate PD. [•] Patients with moderate PD used more steps to regain balance than HC. [•] Weight shift time continues to be longer in moderate PD vs. HC, as in mild PD. [•] Weight shift time may be an early indicator of postural instability in PD. [Copyright &y& Elsevier]

Abstract: Experiments designed to assess balance recovery in older adults often involve exposing participants to repeated loss of balance. The purpose of this study was to investigate the adaptive balance recovery response exhibited by older adults following repeated exposure to forward loss of balance induced by releasing participants from a static forward lean angle. Fifty–eight healthy, community-dwelling older adults, aged 65–80 years, participated in the study. Participants were instructed to attempt to recover with a single step and performed four trials at each of three lean angles. Adaptive recovery responses at four events (cable release, toe-off of the stepping foot, foot contact and maximum knee flexion angle following landing in the stepping leg) were quantified for trials performed at the intermediate lean angle using the concept of margin of stability. The antero-posterior and medio-lateral margin of stability were computed as the difference between the velocity-adjusted position of the whole body centre of mass and the corresponding anterior or lateral boundary of the base of support. Across repeated trials adaptations in reactive stepping responses were detected that resulted in improved antero-posterior stability at foot contact and maximum knee flexion angle. Improved antero-posterior stability following repeated trials was explained by more effective control of the whole body centre of mass during the reactive stepping response and not by adjustments in step timing or base of support. The observed adaptations occurred within a single testing session and need to be considered in the design of balance recovery experiments. [Copyright &y& Elsevier]

Previous research on human balance recovery suggests that, prior to an externally triggered postural perturbation, healthy subjects can pre-select their postural response based on the environmental context, but it is unclear whether this pre-selection includes the selection of a stepping leg when performing compensatory steps. We sought to determine how pre-selecting a stepping limb affects the compensatory steps and stability of young, healthy subjects when responding to postural perturbations. Nine healthy subjects (24–37 years of age) stepped in response to backward translations of a platform under their feet when, prior to the perturbations, the subjects either knew whether they were to step with their left or right leg to a visual target (the Predictable condition) or did not know whether to step with their left or right leg until one of two targets appeared at perturbation onset (the Unpredictable condition). The Unpredictable condition also included randomly inserted trials of toes-up rotations and backward translations without targets (catch trials). The results showed that, in the Predictable condition, the subjects consistently exhibited one anticipatory postural adjustment (APA; a lateral weight shift toward the stance limb) before stepping accurately to the target with the correct leg. In the Unpredictable condition, the subjects either (1) exhibited multiple APAs, late step onsets, and forward center-of-mass (CoM) displacements that were farther beyond their base of support, or (2) exhibited an early step with only one APA and kept their CoM closer to the base of support, but also stepped more often with the incorrect leg. Thus, when the subjects had to select a stepping leg at perturbation onset, they either became more unstable and used multiple APAs to delay stepping in order to provide enough time to select the correct stepping leg, or they stepped earlier to remain stable but often stepped with the incorrect leg. In addition, responses to catch trials in the Unpredictable condition included distorted step placements that resembled steps to anticipated targets, despite allowing the subjects to step with a leg of their choice and to a location of their choice. Lastly, the subjects’ voluntary stepping latencies to visual targets presented without perturbations were twice as long as their stepping latencies to the backward platform translations. Therefore, healthy subjects appear to pre-select their stepping limb, even when the perturbation characteristics are unpredictable, because relying on visual input provided at perturbation onset requires a delayed response that leads to greater instability. [ABSTRACT FROM AUTHOR]

Abstract: An effective stepping response is often critical in avoiding a fall. Our objective was to study the effects of age and balance impairment on anterior and posterior compensatory stepping strategies in response to waist pull perturbations of 1–5% body weight (BW). Based on maximal unipedal stance time (UST), we tested 15 balance-impaired old (BI, UST<10s, mean age=76 years), 12 healthy old (O, UST>30s, mean age=71 years), and 13 healthy young women (Y, UST>30s, mean age=23 years). Randomized anterior and posterior pulls of 1–5% body weight (BW) were applied to the waist while kinematic and kinetic recovery responses were recorded. Results show that O and BI required 0.5 more steps than Y to recover balance for posterior pulls of 4–5% BW (P <0.01). For anterior pulls of 4–5% BW, only BI had a greater probability of step initiation (P ≤0.05 or <0.02) and mean number of steps required to recover balance (P <0.03). The Y used 93% greater torso extension and 24% greater torso flexion in responding to anterior and posterior pulls, respectively. In the posterior, but not anterior direction, O employed smaller (P <0.007), but more laterally-directed (P <0.03) steps than the Y. The BI were less able to attenuate their momentum during the step landing in both directions. We conclude that the additional steps required by the BI in both directions occurred because their initial step failed to properly arrest their momentum. Controlling torso inclination before step liftoff and linear momentum after step landing are critical components of successful compensatory stepping. [Copyright &y& Elsevier]

A compensatory stepping response is a commonly used strategy in recovering balance control after a postural perturbation. Unlike gait initiation, the compensatory stepping often occurs without an anticipatory postural adjustment (APA), in which body weight is shifted to the swing leg first and then back to the stance leg prior to foot lifting. In postural perturbation studies using a moving platforms stepping responses without an APA were found to have shorter latency to foot lifting than trials with an APA. We studied stepping responses of healthy young adults under postural perturbation of a pulling force impulse on the subject''s waist. In contrast to previous studies, the latency of foot lifting was found in the current study to be shorter in the trials with an APA than trials without an APA. Furthermore, greater amplitude of an APA was associated with a shorter latency of foot lifting. Response with an APA of large amplitude may indicate high level of determinant for foot lifting. A pause as to whether or not to initiate/complete a stepping response is suggested to be partially the cause of delayed foot lifting in trials without an APA or with small amplitude of the APA. [Copyright &y& Elsevier]

Background . Persons with stroke (PwS) are at increased risk of falls, especially toward the paretic side, increasing the probability of a hip fracture. The ability to recover from unexpected loss of balance is a critical factor in fall prevention. Objectives . We aimed to compare reactive balance capacity and step kinematics between PwS and healthy controls. Methods . Thirty subacute PwS and 15 healthy controls were exposed to forward, backward, right, and left unannounced surface translations in 6 increasing intensities while standing. Single step threshold, multiple step threshold, and fall threshold (ie, perturbation intensity leading to a fall into harness system) were recorded as well as reactive step initiation time, step length, and step velocity. Results . Twenty-five PwS fell into harness system during the experiment while healthy controls did not fall. Fourteen out of 31 falls occurred in response to surface translations toward the nonparetic side, that is, falling toward the paretic side. Compared with healthy controls, PwS demonstrated significantly lower fall threshold and multiple step threshold in response to forward, backward, and lateral surface translations. Impairments were more pronounced in response to forward surface translation and toward the nonparetic side (ie, loss of balance toward the paretic side). A trend toward significant shorter step length in response to lateral surface translations was found in PwS compared with healthy controls. Conclusions . Findings highlight the importance of assessing reactive balance capacity in response to perturbations in different directions and intensities in addition to the routine assessment in PwS.

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.

Background: Age-related difficulty in controlling lateral stability is of crucial importance because lateral falls increase risk of debilitating hip-fracture injury. This study examined whether a small increase in footwear sole width can improve ability of older adults to regain lateral stability subsequent to balance perturbation., Methods: The study involved sixteen healthy, ambulatory, community-dwelling older adults (aged 65-78). Widened base-of-support (WBOS) footwear was simulated by affixing polystyrene-foam blocks (20mm wide) on the medial and lateral sides of rubber overshoes; unaltered overshoes were worn in normal (NBOS) trials. Balance perturbations were applied using a motion platform., Results: Gait, mobility and agility tests revealed no adverse effects of wearing the WBOS footwear. Lateral-perturbation tests showed that the WBOS footwear improved ability to stabilize the body without stepping (p=0.002). Depending on the perturbation magnitude, the frequency of stepping was reduced by up to 25% (64% of NBOS trials vs 39% of WBOS trials). In addition, the WBOS footwear appeared to improve ability to maintain lateral stability during forward-step reactions, as evidenced by reduced incidence of additional lateral steps (p=0.04) after stepping over an obstacle in response to a forward-fall perturbation., Conclusions: A small increase in sole width can improve certain aspects of lateral stability in older adults, without compromising mobility and agility. This finding supports the viability of WBOS footwear as an intervention to improve balance. Further research is needed to test populations with more severe balance impairments, examine user compliance, and determine if WBOS footwear actually reduces falling risk in daily life.