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Reactive steps are rapid responses after balance challenges. People with Parkinson's Disease (PwPD) demonstrate impaired reactive stepping, increasing fall-risk. Although PwPD can improve steps through practice, the neural mechanisms contributing to improved reactive stepping are poorly understood. This study investigated white-matter correlates of responsiveness to reactive step training in PwPD. In an eighteen-week multiple-baseline study, participants (n = 22) underwent baseline assessments (B1 and B2 two-weeks apart), a two-week training protocol, and post-training assessments immediately (P1) and two-months (P2) post-training. Assessments involved three backward reactive step trials, measuring anterior-posterior margin of stability (AP MOS), step length, and step latency. Tract-Based Spatial Statistics correlated white-matter integrity (fractional anisotropy (FA) and radial diffusivity (RD)) with retained (P2-B2) and immediate improvements (P1-B2) in stepping. Significant and sustained improvements in step length and AP MOS were observed. Greater retention of step length improvement correlated with increased FA in the left anterior thalamic radiation (ATR), left posterior thalamic radiation (PTR), left superior longitudinal fasciculus (SLF), and right inferior longitudinal fasciculus (ILF). Step latency retention was associated with lower RD in the left posterior corona radiata and left PTR. Immediate improvements in AP MOS correlated with increased FA of the right ILF, right SLF, and right corticospinal tract. Immediate step length improvements were associated with increased FA in right and left ATR and right SLF. These findings highlight the importance of white-matter microstructural integrity in motor learning and retention processes in PD and could aid in identifying individuals with PD who would benefit most from balance rehabilitation., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Background and Purpose: Reactive balance training improves reactive postural control in people with Parkinson disease (PwPD). However, the extent to which reactive balance training generalizes to a novel, unpracticed reactive balance task is unknown. This study aimed to determine whether reactive training stepping through support surface translations can be generalized to an unpracticed, instrumented tether-release task., Methods: Twenty-five PwPD (70.52 years ± 7.15; Hoehn and Yahr range 1-3) completed a multiple baseline, open-label, uncontrolled pre-post intervention study. Stepping was trained through a 2-week (6-session) intervention with repeated support surface translations. Performance on an untrained tether-release task (generalization task) was measured at 2 baseline assessments (B1 and B2, 2 weeks apart), immediately after the intervention (P1), and 2 months after training (P2). The tether-release task outcomes were the anterior-posterior margin of stability (MOS), step length, and step latency during backward and forward steps., Results: After support surface translation practice, tether-release stepping performance improved in MOS, step length, and step latency for both backward and forward steps compared to baseline ( P < 0.05). Improvements in MOS and step length during backward and forward steps in the tether-release task, respectively, were related to stepping changes in the practiced task. However, the improvements in the generalization task were not retained for 2 months., Discussion and Conclusions: These findings support short-term generalization from trained balance tasks to novel, untrained tasks. These findings contribute to our understanding of the effects and generalization of reactive step training in PwPD., Video Abstract Available: for more insights from the authors (see the Video, Supplemental Digital Content available at http://links.lww.com/JNPT/A465 )., Competing Interests: The authors declare no conflict of interest., (Copyright © 2024 Academy of Neurologic Physical Therapy, APTA.)

Objective: To develop a multiple sclerosis (MS)-specific model of balance and examine differences between (1) MS and neurotypical controls and (2) people with MS (PwMS) with (MS-F) and without a fall history (MS-NF)., Design and Setting: A cross-sectional study was conducted at the Gait and Balance Laboratory at the University of Kansas Medical Center. Balance was measured from the instrumented sway system (ISway) assessment., Participants: In total, 118 people with relapsing-remitting MS (MS-F=39; MS-NF=79) and 46 age-matched neurotypical controls., Intervention: Not applicable., Outcome Measures: A total of 22 sway measures obtained from the ISway were entered into an exploratory factor analysis to identify underlying balance domains. The model-derived balance domains were compared between (1) PwMS and age-matched, neurotypical controls and (2) MS-F and MS-NF., Results: Three distinct balance domains were identified: (1) sway amplitude and velocity, (2) sway frequency and jerk mediolateral, and (3) sway frequency and jerk anteroposterior, explaining 81.66% of balance variance. PwMS exhibited worse performance (ie, greater amplitude and velocity of sway) in the sway velocity and amplitude domain compared to age-matched neurotypical controls (P=.003). MS-F also exhibited worse performance in the sway velocity and amplitude domain compared to MS-NF (P=.046). The anteroposterior and mediolateral sway frequency and jerk domains were not different between PwMS and neurotypical controls nor between MS-F and MS-NF., Conclusions: This study identified a 3-factor, MS-specific balance model, demonstrating that PwMS, particularly those with a fall history, exhibit disproportionate impairments in sway amplitude and velocity. Identifying postural stability outcomes and domains that are altered in PwMS and clinically relevant (eg, related to falls) would help isolate potential treatment targets., (Published by Elsevier Inc.)

Objective: Reactive stepping is critical for preventing falls and is impaired in people with multiple sclerosis (PwMS); however, which aspects of stepping relate to falls remains poorly understood. Identifying outcomes most related to falls is a first step toward improving rehabilitation for fall prevention. The purpose of this study was to assess whether reactive step latency or length during forward and backward losses of balance were related to a history of falls in PwMS., Methods: Of the 111 PwMS who participated in this study, 76 reported no falls in the previous 6 months, whereas 36 reported 1 or more falls. Participants completed 3 forward and 3 backward treadmill-induced reactive steps from stance. Step length (centimeters) and step latency (milliseconds) were measured using motion capture and analyzed via MATLAB., Results: Participants with a history of falls had significantly slower step latencies during backward stepping, but not forward stepping, than those without a history of falls. Step length did not differ between groups. Slower step latencies during backward stepping significantly increased the odds of having experienced a fall (β = .908, SE = 0.403, odds ratio = 2.479, 95% CI = 1.125 to 5.464)., Conclusion: PwMS and a history of falling show delayed step onsets during backward reactive stepping. Specifically, for every 10-millisecond increase in step latency, PwMS were 2.5 times more likely to have a fall history. Although clinical trials are necessary to determine whether interventions targeting reactive stepping reduce falls in PwMS, the current work indicates that the latency of steps may be a relevant target for this work., Impact: Subsequent fall prevention clinical trials should consider targeting backward reactive step latency to further assess its relevance for rehabilitation in PwMS., Lay Summary: If you have MS and a history of falls, you may be more likely to have delayed reactive step latencies., (© The Author(s) 2022. Published by Oxford University Press on behalf of the American Physical Therapy Association. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Quick responses to a loss of balance or "automatic postural responses" (APRs) are critical for fall prevention. The addition of a distracting task- dual-tasking (DT), typically worsens performance on mobility tasks. However, the effect of DT on APRs is unclear. We conducted a systematic review and meta-analyses to examine the effects of DT on spatial, temporal, and neuromuscular components of APRs and the effect of DT on cognitive performance. A Meta-analysis of 19 cohorts (n = 329) showed significant worsening in spatial kinematic features of APRs under DT conditions (P = 0.01), and a meta-analysis of 9 cohorts (n = 123) demonstrated later muscle onset during DT (P = 0.003). No significant DT effect was observed for temporal kinematic outcomes in 18 cohorts (n = 328; P = 0.47). Finally, significant declines in cognitive performance were evident in 20 cohorts (n = 400; P = 0.002). These results indicate that, despite the somewhat reactive nature of APRs, the addition of a secondary task negatively impacts some aspects of the response. These findings underscore the importance of cortical structures in APR generation. Given the importance of APRs for falls, identifying aspects of APRs that are altered under DT may inform fall-prevention treatment approaches., (Published by Elsevier Inc.)

This perspective article provides a brief review of our understanding of how center of pressure (CoP) and center of mass (CoM) are traditionally utilized to measure quiet standing and how technological advancements are allowing for measurements to be derived outside the confines of a laboratory setting. Furthermore, this viewpoint provides descriptions of what CoP and CoM outcomes may reflect, a discussion of recent developments in selected balance outcomes, the importance of measuring instantaneous balance outcomes, and directions for future questions/research. Considering the enormous number and cost of falls annually, conclusions drawn from this perspective underscore the need for more cohesive efforts to advance our understanding of balance performance. As we refine the technology and algorithms used to portably assess postural stability, the question of which measurement (i.e. CoP or CoM) to utilize seems to be highly dependent on the question being asked. Further, the complexity of the question appears to span multiple disciplines and cultivate exploration of the intrinsic mechanisms of stability. Recently developed multi-dimensional methods for assessing balance performance may provide additional insight into balance, improving our ability to predict balance impairments and falls outside the laboratory and in the clinic. However, additional work will be necessary to understand the clinical significance and predictive capacity of these outcomes in various fall-prone populations., (Published by Elsevier Ltd.)

Background: Automatic postural responses are critical to prevent falls after a loss of balance. Although responses have been shown to be delayed in people with multiple sclerosis (PwMS), the degree to which other aspects of these movements are impacted by MS remains unknown., Research Question: Do responses to in-place support-surface perturbations differ in PwMS compared to neurotypical adults? Are these responses related to a functional measure of postural response performance- center of mass (COM) displacement?., Method: 52 PwMS and 20 neurotypical, age-matched adults (NA) experienced backward support surface perturbations resulting in forward loss of balance and requiring an in-place response. Center of pressure (COP) and torque were calculated from force plates while center of mass (COM) approximations were collected via motion capture. Primary outcomes were maximal torque production at the foot and its timing, rate, and onset., Results: PwMS and NA demonstrated no differences in maximal torque production (p = 0.79), timing of maximal torque (p = 0.29), rate of torque development (p = 0.76), or the onset of AP COP movement (p = 0.44). There was a significant negative association between the rate of torque development and forward COM displacement in both groups (Control: r=-0.64, p = 0.002; MS: r=-0.35, p = 0.01). Larger maximal torque production was also associated with smaller COM displacement in PwMS (r=-0.33, p = 0.02)., Conclusion: Torque profiles in response to backward support surface translations resulting in feet in-place responses were similar in people with mild MS and neurotypical adults. The rate of development and maximal torque were however correlated to functional postural response outcomes. These findings suggest that while not worse in PwMS during in-place perturbations, force-responses seem to be important predictors of the effectiveness of reactive postural control responses., (Published by Elsevier B.V.)

Background: Multiple sclerosis (MS) is an autoimmune-based chronic inflammatory disease characterized by the neurodegeneration of the central nervous system and produces postural dysfunction. Quiet or static standing is a complex task carried out through afferent sensory inputs and efferent postural corrective outputs. Currently the mechanisms underlying these outputs remain largely unknown., Research Question: Assess the relationship between multi-dimensional measures of postural control and microstructural integrity of the cortical sensorimotor pathway (CSP) in persons with MS (PwMS) and neurotypical adults., Methods: Postural control performance was assessed by both overall and directional time-to-boundary measures across four manipulated sensory stance conditions (eyes open/closed; stance firm/foam) in twenty-nine neurotypical and twenty-seven PwMS. These postural outcomes were evaluated with mixed-model repeated measures analysis of variance across group (MS and control) and stance condition. Postural performance was also correlated with magnetic resonance imaging diffusion tensor-derived measures of microstructural integrity of the CSP., Results: PwMS displayed significantly (p =  0.026) worse anterior-posterior postural control compared to their neurotypical counterparts across sensory testing conditions and poorer CSP microstructural integrity in comparison to neurotypical adults (p =  0.008). Additionally, PwMS displayed a significant association (2D (rho = -0.384, p =  0.048), AP (rho = -0.355, p =  0.035), and ML (rho = -0.365, p =  0.030) between integrity of the CSP and postural control performance during proprioceptive-based balance, such that those with worse cortical structure had poorer balance control., Significance: This is the first study to establish connections between the microstructural integrity of the CSP and multi-dimensional postural control performance. Results indicate that a reduction in the CSP microstructural integrity is associated with poorer postural control in PwMS. These outcomes identify neural underpinnings of postural control dysfunction in PwMS and provide new avenues for evaluating the efficacy of postural rehabilitation strategies in PwMS that express proprioceptive-based postural deficits., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Background: People with PD who exhibit freezing of gait (FOG) also exhibit poor balance compared to those who do not freeze. However, balance is a broad construct that can be subdivided into subdomains that include dynamic balance (gait), anticipatory postural adjustments (APAs) & gait initiation, postural sway in stance, and automatic postural responses (e.g., reactive stepping). Few studies have provided a robust investigation on how each of these domains is impacted by FOG, and no studies have compared balance across groups while rigorously controlling for disease severity., Methods: Structural equation modeling was used to evaluate the relationships between FOG and balance domains constructed as latent variables and controlling for disease severity. Domains included: dynamic balance (gait), APAs, postural sway, and reactive stepping. Models were run relating domains to both the presence and severity of FOG., Results: Latent variables reflecting domains of Gait and APAs, but not postural sway or reactive stepping, were significantly related to the severity of FOG. Models for presence of FOG showed the same results, as Gait and APAs, but not postural sway or reactive stepping, were related to presence of FOG., Conclusion: These results are consistent with hypotheses that balance deficits in people with PD who freeze are most pronounced in gait and anticipatory postural adjustments. Reactive stepping and postural sway domains are less effected in PD patients who freeze compared to those who do not. These findings suggest that rehabilitative strategies focused on gait and APAs may be most effective for people with PD who freeze., (Published by Elsevier Ltd.)

Introduction . Reactive movements in response to a loss of balance are altered in people with Parkinson's disease (PD) and are critical for fall prevention. Further, falls are more common while attention is divided. Although divided attention has been shown to impact postural responses in healthy older adults, the impact of dividing attention on reactive balance, and the natural prioritization across postural and cognitive tasks in people with PD is largely unknown. Objectives . To characterize (1) the impact of a secondary cognitive task on reactive postural control and (2) the prioritization across stepping and cognitive tasks in people with PD. Methods . Sixteen people with PD and 14 age-matched controls underwent step-inducing, support-surface perturbations from stance, with and without an auditory Stroop secondary cognitive task. Cognitive, neuromuscular, and protective stepping performance were calculated for single and dual task scenarios. Results . In PD and control participants, cognitive reaction times ( P = .001) and muscle onset latency ( P = .007), but not protective step outcomes ( P > .12 for all) were worse during dual tasking compared with single-task scenarios. Both PD and control groups prioritized the protective stepping task over the cognitive task. Overall, people with PD exhibited worse first-step margin of stability (a measure of protective step performance) than controls ( P = .044). Conclusion . This study provides preliminary evidence that people with PD, like age-matched controls, exhibit cognitive and neuromuscular, but not protective step, dual-task interference. The lack of dual-task interference on step performance indicates a postural prioritization for PD and healthy older adults during dual-task protective stepping.

Introduction . It is well documented that freezing of gait (FoG) episodes occur in situations that are mentally challenging, such as dual tasks, consistent with less automatic control of gait in people with Parkinson disease (PD) and FoG. However, most physical rehabilitation does not include such challenges. The purpose was to determine (1) feasibility of a cognitively challenging Agility Boot Camp-Cognitive (ABC-C) program and (2) effects of this intervention on FoG, dual-task cost, balance, executive function, and functional connectivity. Methods . A total of 46 people with PD and FoG enrolled in this randomized crossover trial. Each participant had 6 weeks of ABC-C and Education interventions. Outcome measures were the following: FoG, perceived and objective measures; dual-task cost on gait; balance; executive function; and right supplementary motor area (SMA)-pedunculopontine nucleus (PPN) functional connectivity. Effect sizes were calculated. Results . ABC-C had high compliance (90%), with a 24% dropout rate. Improvements after exercise, revealed by moderate and large effect sizes, were observed for subject perception of FoG after exercise, dual-task cost on gait speed, balance, cognition (Scales for Outcomes in Parkinson's disease-Cognition), and SMA-PPN connectivity. Conclusions . The ABC-C for people with PD and FoG is a feasible exercise program that has potential to improve FoG, balance, dual-task cost, executive function, and brain connectivity. The study provided effect sizes to help design future studies with more participants and longer duration to fully determine the potential to improve FoG.

Background: The use of vestibular rehabilitation principles in the management of gaze and postural stability impairments in people with multiple sclerosis (PwMS) has shown promise in pilot work completed in our lab and in a recently published randomized clinical trial (RCT). However, further work is needed to fully quantify the gaze and postural impairments present in people with multiple sclerosis and how they respond to rehabilitation., Methods/design: The study is a single blind RCT designed to examine the benefit of a gaze and postural stability (GPS) intervention program compared to a standard of care (SOC) rehabilitation program in dizzy and balance impaired PwMS. Outcomes will be collected across the domains of body structure and function, activity, and participation as classified by the World Health Organization International Classification of Functioning, Disability, and Health (ICF). Our primary outcomes are the Dizziness Handicap Inventory (DHI) and the Functional Gait Assessment (FGA). Secondary outcomes include other measures of gaze and postural stability, fatigue, and functional mobility. Participants who are interested and eligible for enrollment will be consented prior to completing a baseline assessment. Following the baseline assessment each participant will be randomized to either the GPS or SOC intervention group and will complete a 6 week treatment period. During the treatment period, both groups will participate in guided exercise 3x/week. Following the treatment period participants will be asked to return for a post-treatment evaluation and again for a follow-up assessment 1 month later. We anticipate enrolling 50 participants., Discussion: This study will be an innovative RCT that will utilize gaze and postural stability metrics to assess the efficacy of vestibular rehabilitation in PwMS. It will build on previous work by examining measures across the ICF and improve the current evidence base for treating PwMS., Trial Registration: ClinicalTrials.gov, May 29th 2018, NCT03521557 .

Objectives: To evaluate the impact of a single day of protective stepping practice in individuals with Multiple Sclerosis (MS)., Background: Multiple Sclerosis is a leading cause of disability among young adults in the United States. Gait and balance dysfunction are both widespread in MS and strong predictors of falls, disability, and quality of life among those with MS., Method: Fourteen participants with MS and 11 neurotypical, age-matched control participants were exposed to repeated support surface perturbations over the course of 2 days: one "training" day and one "retention" day. Perturbations were elicited on an instrumented treadmill and marker data were collected to evaluate five outcomes (Margin of Stability, Step Length, Step Latency, Leg Angle, and Trunk Angle)., Analytic Method: Repeated measures data were analyzed using linear growth models and mixed effects models to evaluate the effects of group (MS or Control), trial, and the interaction of group by trial., Results: Significant improvements in Step Length and Leg Angle and a trend for improvement in Margin of Stability among those with MS were observed. Step Latency and Trunk Angle did not show significant changes. Retention analyses revealed significant retention of improvements in Step Length and Leg Angle among MS participants., Discussion: Protective step characteristics have been shown to be important predictors of fall risk in populations affected by neurological disorders. The present study indicates that these characteristics may be amenable to intervention through exposure to repeated, perturbations requiring protective stepping. Further research is needed to establish the predictive utility of these biomechanical markers for falls in MS specifically; however, the present findings suggest that perturbation training may be a valuable means of decreasing fall risk among those affected by MS., (Copyright © 2019. Published by Elsevier B.V.)

Background: Effective protective steps are critical for fall prevention, and anticipatory postural adjustments (APAs) after a perturbation but prior to protective steps affect step performance. Although APAs prior to protective steps are altered in people with Parkinson's disease (PD), whether these changes affect subsequent step performance is poorly understood., Objective: Characterize the relationship between mediolateral APA size and protective step outcomes in response to anteroposterior balance perturbations in people with PD., Methods: Twenty-eight individuals with PD completed 25 forward and 25 backward protective steps in response to support surface translations. Multilevel linear models related mediolateral APA size to protective step outcomes., Results: During forward protective stepping, larger mediolateral APAs were associated with delayed ( P < .001) and larger ( P = .004) steps. Larger APAs were also associated with smaller mediolateral ( P < .001) but larger anterior-posterior center of mass movement at foot off ( P < .001). During backward stepping, larger APAs were associated with later steps ( P < .001) and smaller anterior-posterior margin of stability at first foot contact ( P < .001). During backward stepping, larger APAs were also associated with worse clinical (ie, UPDRS [Unified Parkinson's Disease Rating Scale]; P = .005) and balance (ie, MiniBEST [Mini-Balance Evaluation Systems Test]; P = .021) outcomes., Conclusions: During forward protective stepping, larger APAs were associated with larger and later steps, suggesting APA size may have mixed effects on the subsequent step. During backward stepping, larger APAs were associated with worse stepping outcomes (ie, later steps, smaller anterior-posterior margin of stability, worse clinical outcomes). Interventions aimed at improving APAs in PD should monitor spatial and temporal protective step outcomes to ensure treatment does not negatively affect protective steps, particularly for forward stepping.

Background: Falls are a significant burden for people with Parkinson's disease (PD), however, individuals across the spectrum of disease severity respond differently to fall prevention interventions. Despite the multifactorial causes of falls in people with PD, recent work has provided insight into interventions that hold promise for fall prevention. Further, studies have begun to identify patient characteristics that may predict responsiveness to such interventions., Research Question: We discuss (i) the postural motor learning abilities of people with mild versus severe PD that could affect their ability to benefit from fall prevention interventions, (ii) how people with different severity of PD respond to such interventions, and (iii) the practical considerations of providing effective fall prevention interventions for people with PD across the spectrum of disease severity., Methods: This narrative review consolidates recent work on postural motor learning and fall prevention rehabilitation involving exercise in people with PD., Results: People with PD are able to improve postural motor control through practice, enabling them to benefit from exercise which challenges their gait and balance to reduce falling. Worsening of axial and cognitive symptoms may result in diminished learning, and those with more severe PD may require fully supervised, high intensity programs to reduce falls., Significance: Understanding how people with PD across the spectrum of disease severity differ in their postural motor learning ability and response to different fall prevention interventions will enable researchers and clinicians to refine such interventions and their delivery to minimize falls and their negative sequelae in people with PD., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The inverted pendulum model predicts that the major challenge for neural control of the upright posture is the inherent instability of the body due to the center of mass (COM) being above the base of support (BOS). If so, even slight elevation of the COM may substantially destabilize posture. The destabilizing effect of heavy load positioned above the COM has been demonstrated. We examined sensitivity of posture to light (1-5% of body weight) load by placing weights on the shoulders and assessing functional reach distance in the forward, right, and left directions and postural sway during quiet stance. At each load level, the quiet stance task was tested with and without vision. The 1% of body weight load significantly shortened reach distance in the forward direction. It also increased postural sway. Interestingly, additional weight did not result in further deficits. The results support high sensitivity of postural stability to COM elevation that increases the challenge for neural control of posture and that can potentially be used for early detection of declines in postural stability.

Objective: To test the validity of wearable inertial sensors to provide objective measures of postural stepping responses to the push and release clinical test in people with multiple sclerosis., Design: Cross-sectional study., Setting: University medical center balance disorder laboratory., Participants: Total sample N=73; persons with multiple sclerosis (PwMS) n=52; healthy controls n=21., Main Outcome Measures: Stepping latency, time and number of steps required to reach stability, and initial step length were calculated using 3 inertial measurement units placed on participants' lumbar spine and feet., Results: Correlations between inertial sensor measures and measures obtained from the laboratory-based systems were moderate to strong and statistically significant for all variables: time to release (r=.992), latency (r=.655), time to stability (r=.847), time of first heel strike (r=.665), number of steps (r=.825), and first step length (r=.592). Compared with healthy controls, PwMS demonstrated a longer time to stability and required a larger number of steps to reach stability., Conclusions: The instrumented push and release test is a valid measure of postural responses in PwMS and could be used as a clinical outcome measures for patient care decisions or for clinical trials aimed at improving postural control in PwMS., (Copyright © 2016 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.)

Objective: To characterize anticipatory postural adjustments (APAs) across a variety of step initiation tasks in people with Parkinson disease (PD) and healthy subjects., Design: Cross-sectional study. Step initiation was analyzed during self-initiated gait, perceptual cued gait, and compensatory forward stepping after platform perturbation. People with PD were assessed on and off levodopa., Setting: University research laboratory., Participants: People (N=31) with PD (n=19) and healthy aged-matched subjects (n=12)., Interventions: Not applicable., Main Outcome Measures: Mediolateral (ML) size of APAs (calculated from center of pressure recordings), step kinematics, and body alignment., Results: With respect to self-initiated gait, the ML size of APAs was significantly larger during the cued condition and significantly smaller during the compensatory condition (P<.001). Healthy subjects and patients with PD did not differ in body alignment during the stance phase prior to stepping. No significant group effect was found for ML size of APAs between healthy subjects and patients with PD. However, the reduction in APA size from cued to compensatory stepping was significantly less pronounced in PD off medication compared with healthy subjects, as indicated by a significant group by condition interaction effect (P<.01). No significant differences were found comparing patients with PD on and off medications., Conclusions: Specific stepping conditions had a significant effect on the preparation and execution of step initiation. Therefore, APA size should be interpreted with respect to the specific stepping condition. Across-task changes in people with PD were less pronounced compared with healthy subjects. Antiparkinsonian medication did not significantly improve step initiation in this mildly affected PD cohort., (Copyright © 2016 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.)

Background: Improvement of postural control in persons with multiple sclerosis (PwMS) is an important target for neurorehabilitation. Although PwMS are able to improve postural performance with training, the neural underpinnings of these improvements are poorly understood., Objective: To understand the neural underpinnings of postural motor learning in PwMS., Methods: Supraspinal white matter structural connectivity in PwMS was correlated with improvements in postural performance (balancing on an oscillating surface over 25 trials) and retention of improvements (24 hours later)., Results: Improvement in postural performance was directly correlated to microstructural integrity of white matter tracts, measured as radial diffusivity, in the corpus callosum, posterior parieto-sensorimotor fibers and the brainstem in PwMS. Within the corpus callosum, the genu and midbody (fibers connecting the prefrontal and primary motor cortices, respectively) were most strongly correlated to improvements in postural control. Twenty-four-hour retention was not correlated to radial diffusivity., Conclusion: PwMS who exhibited poorer white matter tract integrity connecting the cortical hemispheres via the corpus callosum showed the most difficulty learning to control balance on an unstable surface. Prediction of improvements in postural control through training (ie, motor learning) via structural imaging of the brain may allow for identification of individuals who are particularly well suited for postural rehabilitation interventions.

Background The effect of levodopa on postural motor learning in people with Parkinson's disease is poorly understood. In particular, it is unknown whether levodopa affects improvement in protective postural responses after external perturbations such as a slip or trip, a critical aspect of fall prevention. Objective Determine the effect of levodopa on postural motor learning in people with Parkinson's disease. Methods We assessed improvement in protective postural responses in people with Parkinson's disease over short-term (1 day) perturbation training on and off levodopa. We also assessed retention and generalization of improvement. Participants were 22 individuals with Parkinson's disease. The primary outcome was total center of mass (COM) displacement after perturbation. Secondary outcomes assessed first step performance and included margin of stability at first foot contact. Results People with Parkinson's disease improved COM displacement (P = .011) and margin of stability (P = .016) over training. Improvements in these outcomes were more pronounced after training while on levodopa than off levodopa. Levodopa State × Training interactions were not observed for other step performance variables (eg, step latency, length, total number of steps). Improvements were retained for 24 hours, and for margin of stability, retention was more pronounced while on levodopa than off (P = .018). Conclusions Individuals with Parkinson's disease are able to improve protective postural responses through short-term perturbation training, and improvements were more pronounced when on levodopa for some variables. Perturbation training may be more effective if completed while optimally medicated with levodopa., Competing Interests: Dr. Horak and OHSU have an equity/interest in APDM, a company that may have a commercial interest in the results of the study. This potential conflict of interest has been reviewed and managed by the Research & Development Committee at the Portland VA Medical Center and OHSU. No other authors declare any conflict of interest., (© The Author(s) 2016.)

Protective postural responses to external perturbations are hypokinetic in people with Parkinson's disease (PD), and improving these responses may reduce falls. However, the ability of people with PD to improve postural responses with practice is poorly understood. Our objective was to determine whether people with PD can improve protective postural responses similarly to healthy adults through repeated perturbations, and whether improvements are retained or generalize to untrained perturbations. Twelve healthy adults and 15 people with PD underwent 25 forward and 25 backward translations of the support surface, eliciting backward, and forward protective steps, respectively. We assessed whether: (1) performance improved over one day of practice, (2) changes were retained 24 h later, and (3) improvements generalized to untrained (lateral) postural responses. People with PD and healthy adults improved postural response characteristics, including center of mass displacement after perturbations (p < 0.001), margin of stability at first footfall (p = 0.001), step latency (p = 0.044), and number of steps (p = 0.001). However, unlike controls, improvements in people with PD occurred primarily in the first block of trials. Improvements were more pronounced during backward protective stepping than forward, and with the exception of step latency, were retained 24 h later. Improvements in forward-backward stepping did not generalize to lateral protective stepping. People with PD can improve protective stepping over the course of 1 day of perturbation practice. Improvements were generally similar to healthy adults, and were retained in both groups. Perturbation practice may represent a promising approach to improving protective postural responses in people with PD; however, additional research is needed to understand how to enhance generalization.

Objective: To characterize postural responses to forward and backward external perturbations in people with multiple sclerosis (PwMS), and to relate performance to commonly used clinical outcomes., Design: Cross-sectional study. Postural responses were tested during large stepping and smaller feet-in-place perturbations in forward and backward directions., Setting: University research laboratory., Participants: PwMS (n=54) and age-matched controls (n=21) (N=75)., Interventions: Not applicable., Main Outcome Measures: Center of mass displacement and step latency after external perturbations., Results: PwMS exhibited larger center of mass displacements and step latencies than control participants in response to stepping perturbations (P=.003 and P=.028, respectively). Stepping deficits were more pronounced during backward stepping and were significantly correlated to increased severity on clinical measures (European Database for Multiple Sclerosis disability score and Timed 25-Foot Walk)., Conclusions: Compensatory stepping is impaired in PwMS and correlates with clinical disability. Measurement of backward compensatory stepping may be more effective at identifying postural dysfunction in PwMS than forward compensatory steps. Prolonged step latencies, large anticipatory postural adjustments, and multiple compensatory steps are especially altered in PwMS, suggesting possible targets for neurorehabilitation., (Copyright © 2016 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.)

Approximately 50% of people with Parkinson disease experience freezing of gait, described as a transient inability to produce effective stepping. Complex gait tasks such as turning typically elicit freezing more commonly than simple gait tasks, such as forward walking. Despite the frequency of this debilitating and dangerous symptom, the brain mechanisms underlying freezing remain unclear. Gait imagery during functional magnetic resonance imaging permits investigation of brain activity associated with locomotion. We used this approach to better understand neural function during gait-like tasks in people with Parkinson disease who experience freezing--"FoG+" and people who do not experience freezing--"FoG-". Nine FoG+ and nine FoG- imagined complex gait tasks (turning, backward walking), simple gait tasks (forward walking), and quiet standing during measurements of blood oxygen level dependent (BOLD) signal. Changes in BOLD signal (i.e. beta weights) during imagined walking and imagined standing were analyzed across FoG+ and FoG- groups in locomotor brain regions including supplementary motor area, globus pallidus, putamen, mesencephalic locomotor region, and cerebellar locomotor region. Beta weights in locomotor regions did not differ for complex tasks compared to simple tasks in either group. Across imagined gait tasks, FoG+ demonstrated significantly lower beta weights in the right globus pallidus with respect to FoG-. FoG+ also showed trends toward lower beta weights in other right-hemisphere locomotor regions (supplementary motor area, mesencephalic locomotor region). Finally, during imagined stand, FoG+ exhibited lower beta weights in the cerebellar locomotor region with respect to FoG-. These data support previous results suggesting FoG+ exhibit dysfunction in a number of cortical and subcortical regions, possibly with asymmetric dysfunction towards the right hemisphere.

Objective Reactive stepping is critical for preventing falls and is impaired in people with multiple sclerosis (PwMS); however, which aspects of stepping relate to falls remains poorly understood. Identifying outcomes most related to falls is a first step toward improving rehabilitation for fall prevention. The purpose of this study was to assess whether reactive step latency or length during forward and backward losses of balance were related to a history of falls in PwMS. Methods Of the 111 PwMS who participated in this study, 76 reported no falls in the previous 6 months, whereas 36 reported 1 or more falls. Participants completed 3 forward and 3 backward treadmill-induced reactive steps from stance. Step length (centimeters) and step latency (milliseconds) were measured using motion capture and analyzed via MATLAB. Results Participants with a history of falls had significantly slower step latencies during backward stepping, but not forward stepping, than those without a history of falls. Step length did not differ between groups. Slower step latencies during backward stepping significantly increased the odds of having experienced a fall (β = .908, SE = 0.403, odds ratio = 2.479, 95% CI = 1.125 to 5.464). Conclusion PwMS and a history of falling show delayed step onsets during backward reactive stepping. Specifically, for every 10-millisecond increase in step latency, PwMS were 2.5 times more likely to have a fall history. Although clinical trials are necessary to determine whether interventions targeting reactive stepping reduce falls in PwMS, the current work indicates that the latency of steps may be a relevant target for this work. Impact Subsequent fall prevention clinical trials should consider targeting backward reactive step latency to further assess its relevance for rehabilitation in PwMS. Lay Summary If you have MS and a history of falls, you may be more likely to have delayed reactive step latencies. [ABSTRACT FROM AUTHOR]

Background: Gait initiation and turning are common triggers for Freezing of Gait (FOG) in people with Parkinson's disease (PD). Recently, it has been shown that closed-loop tactile feedback (CLTF) can be effective to improve turning performance in people with FOG.Research Question: Does CLTF change the preparation and execution of the first step during gait initiation?Methods: People (n = 36) with PD with FOG (PD + FOG) (n = 18) and without FOG (PD-FOG) (n = 18) were included in the study and performed self-initiated gait with or without CLTF under single and dual task conditions. Anticipatory postural adjustments (APAs) and step kinematics were quantified with inertial measurement units (IMUs). Muscle activity of the right and left tensor fasciae latae (TFL) was measured via EMG recordings.Results: PD + FOG and PD-FOG did not differ in age, gender and disease duration and severity (p > 0.05). PD + FOG performed smaller APAs (F = 4.559, p = 0.04) with a higher amount of TFL co-contraction (F = 6.034, p = 0.02) compared to PD-FOG. CLTF had no effect on APAs but led to an increase in first step duration (F = 7.921, p = 0.008).Conclusions: PD + FOG had smaller APAs and higher left and right TFL co-contraction during gait initiation. CLTF did not impact preparation of the first step but led to a slower execution of the first step. We speculate that, similarly to findings from turning, CLTF might result in the participant attending more closely to the first step compared to without CLTF. Whether increased attention on gait initiation is beneficial in diminishing FOG should be investigated in more detail. [ABSTRACT FROM AUTHOR]

Virtual time-to-contact (VTC) is a promising approach for investigating postural balance control. However, current VTC calculation approaches are limited as they (1) cannot be used to evaluate directional components of balance, and (2) only assess a single, temporal aspect of balance control. This study introduces a new approach for VTC calculation, namely directional VTC, expanding VTC to assess temporal, spatial, and control aspects of balance. Three case studies were conducted across varying populations and conditions as a proof-of-concept of the presented method. The first study examined quiet stance on a firm surface in people with Parkinson's disease (PD; n = 10) in comparison to their healthy peers (n = 10). The second and third studies assessed balance control of healthy individuals under challenging environments. Ten healthy individuals participated in standing tasks on compliant ground surfaces, while another ten on oscillatory ground surfaces, all simulated by a dual-axis robotic platform. Preliminary results not only provided a closer look at balance control with multiple aspects, including temporal, spatial, and control aspects, but also showed how different aspects of balance changed due to neurological diseases (Case Study I) or challenging standing grounds (Case Studies II and III). This study advances our understanding of posture biomechanics and its clinical applications. [ABSTRACT FROM AUTHOR]

Background: Multiple sclerosis (MS) is a common, debilitating, neurogenerative disorder that causes myriad symptoms. Gait and balance dysfunctions are common and manifest early in the disease, increasing fall risk. In particular, the ability to quickly and effectively react to a loss of balance is worse in people with MS. Therefore, improving reactive balance among those with MS is desirable. However, for maximum ecological validity, improvements in reactive balance through training would be demonstrable upon first loss-of-balance exposure. Objectives: The aim of this study is to evaluate first trial changes in people with MS before and after 1 day of protective stepping practice. The study also seeks to identify clinical correlates of first trial changes to begin evaluating for whom such training may provide benefit. Methods: Fourteen people with MS underwent 2 consecutive days of support-surface perturbations using an instrumented treadmill. Protective stepping outcomes were step length, step latency, and margin of stability. The backward step performance on the first trials on days 1 and 2 were compared, and difference scores were evaluated for relationships with correlates based on theoretical considerations. Results: There were no significant changes in first trial performance after training. However, some clinical and cognitive characteristics, such as mini-BESTest performance, improvement from day 1 to day 2 on the Symbol-Digits Modality test, type of MS diagnosis, and falls history were related with the amount of change individuals experienced. Conclusions: Although preliminary, these findings provide evidence that those with more favorable disease states may see more robust first-trial improvements after perturbation training. Greater doses, larger and more homogeneous samples, or longer delay between training and reassessment may be needed to understand the existence and relevance of first trial changes. [ABSTRACT FROM AUTHOR]

Background: Falls are common in persons with multiple sclerosis (PwMS). Reactive postural control-one's response to a balance perturbation-is likely an aspect of fall risk; however, the relationship between reactive posture and falls is poorly understood in PwMS.Objective: We evaluated tibialis anterior muscle onset latency (TA latency) after balance perturbations as a predictor of fall rates in PwMS, controlling for clinical, functional, sensory, psychological, and cognitive factors.Method: At baseline of the 18-month cohort study, 122 participants with MS (EDSS = 2.23) were included. Assessments were conducted every 6 months.Results: Of the original 122 participants at the baseline collection, data were available from 41, 39, and 34 people at the 6, 12, and 18 month follow-ups, respectively. Percent fallers at the four time points were 35.3%, 12.2%, 15.4%, and 20.5%. Cross-sectionally (i.e., at baseline), the Timed Up-and-Go, Falls Efficacy Scale - International (FES-I), and TA latency after perturbations were significant predictors of retrospective falls rates using negative binomial regression. Longitudinally, random-effects negative binomial regression found that trait-level FES-I, Stroop Color-Word, and TA latency were significant predictors for falls rates.Conclusion: Delays in automatic postural responses seem to account uniquely for fall rates in PwMS-beyond clinical, balance, or mobility measures. These delays may contribute to the increased fall rate in PwMS. In addition to brief self-report instruments (FES-I) and cognitive assessments, muscle onset after balance perturbations may be a valuable tool for predicting falls in those with MS. [ABSTRACT FROM AUTHOR]

Reactive stepping is impaired in people with Parkinson's Disease (PD) but can be improved with training. However, it is unclear if reactive steps can be improved when performing a concurrent cognitive task, a common and fall-relevant circumstance. We assessed the feasibility and preliminary effectiveness of dual-task reactive step training. Specifically, we measured whether stepping and cognitive reaction time are improved after one day of dual-task reactive step practice and if improvements are retained 24 h later. Sixteen people with PD and 13 age-matched healthy controls (HC) underwent repeated from-stance support surface perturbations that elicited a reactive step while performing an auditory Stroop task. Participants returned the following day to reassess dual-task reactive stepping performance. Cognitive, neuromuscular, and stepping outcomes were calculated. Increased step lengths were observed for both groups after practice (p < 0.001). Cognitive reaction times also improved through practice; however, this was more pronounced in the HC group (group by time interaction- p < 0.001). No changes were observed for step latency, margin of stability, or EMG onset through practice. Step length and cognitive reaction time improvements were retained 24 h after practice in both groups (step length: p < 0.001; cognitive reaction time: p = 0.05). This study provides preliminary evidence for the effectiveness of dual-task reactive step training to improve step length in people with PD. The improvements in step length without compromising cognitive reaction times suggest that participants improved reactive stepping without a robust attention shift toward the postural task. Future research is necessary to determine optimal training protocols and determine if such training protocols impact falls in PD patients. [ABSTRACT FROM AUTHOR]

Multiple sclerosis (MS) is a debilitating, neurodegenerative disorder causing considerable gait and balance dysfunction. Reactive balance (i.e., quick movements in response to a loss of balance) is particularly important for fall risk and is impaired in people with MS compared to neurotypical peers. Therefore, improving reactive balance among those with MS is critical. However, for maximum ecological validity, improvements in reactive balance through training would be demonstrable upon first loss-of-balance , rather than an average of several trials as is typically reported. This study evaluated changes in performance on the first stepping trial in people with MS after one day of practice. Fourteen people with MS underwent two, consecutive days of support-surface perturbations from stance. On day 1, participants underwent a single backward-stepping trial, followed by 35 practice trails (forward and backward). Approximately 24 h later, participants were again exposed to a single backward stepping perturbation. Protective stepping outcomes were step length, step latency, and margin of stability at first foot contact. The backward step performance on the first trial of days one and two were compared, and difference scores were evaluated for relationships with correlates based on theoretical considerations. First-trial margin of stability increased (improved) from day 1 to day 2 (P =.016). Steps were also faster on average by approximately 5 ms on day 2, although this improvement was not significant (P =.062). Although preliminary, these findings provide evidence that individuals with MS may be able to experience first-trial improvements after a low dose of perturbation training. • Reactive stepping is relevant to falls & altered in people with multiple sclerosis. • The 1st trial after training is highly clinically relevant but often not assessed. • We show that performance on the 1st reactive step trial after practice was improved. • This provides preliminary evidence that reactive step practice could reduce falls. [ABSTRACT FROM AUTHOR]