How do features of dynamic postural stability change with age during quiet standing, gait, and obstacle crossing?

Previous research has reported mixed findings regarding age-related changes in dynamic postural stability, quantified by margin of stability (MOS), during gait. However, age-related changes in MOS may be better elicited by tasks imposing greater challenges to the postural control system. Older adults' MOS during obstacle crossing, a destabilizing task, has previously been characterized, although studies comparing MOS during this task between younger and older adults remain sparse. This study investigated age-related changes in dynamic postural stability during quiet standing, gait, and obstacle crossing. Participants aged 20-30 (n = 20), 60-69 (n = 18), 70-79 (n = 15), and 80+ (n = 7; not analyzed statistically) years old performed these tasks while whole-body motion was tracked using motion capture. MOS in each direction was estimated throughout each trial, and integrals, transient ranges, and trial minima were extracted (as applicable). MOS time series were also ensemble averaged across age groups. No age-related differences were identified for quiet standing or gait. However, obstacle crossing metrics revealed greater stability (i.e., more positive MOS) and less instability (i.e., less negative MOS) in older adults, and reduced ranges during transients. These findings potentially arise from shorter step lengths, which may be the result of age-related physical declines; or may reflect a cautious strategy in older adults, which maximizes postural stability in the direction with the greatest consequences for foot-obstacle contact, as it changes throughout the task. This study supports the use of tasks imposing physical challenges and/or voluntary perturbations to study age-related changes in dynamic postural stability. Findings also contribute to our theoretical understanding of the time course of dynamic postural stability during functional tasks in relation to periods of transition in the base of support, and task-specific strategies adopted for obstacle crossing by older adults to maintain dynamic postural stability and mitigate fall risk.

Reliability of unconventional centre of pressure measures of quiet standing balance in people with chronic stroke

BACKGROUND

People with stroke often have asymmetric motor impairment. Investigating asymmetries in, and dynamic properties of, centre of pressure movement during quiet standing can inform how balance is controlled.

RESEARCH QUESTION

What are the test-retest reliabilities of unconventional measures of quiet standing balance control in people with chronic stroke?

METHODS

Twenty people with chronic stroke (>6 months post-stroke), who were able to stand for at least 30 s without support, were recruited. Participants completed two 30-second quiet standing trials in a standardized position. Unconventional measures of quiet standing balance control included: symmetry of variability in centre of pressure displacement and velocity, between-limb synchronization, and sample entropy. Root mean square of centre of pressure displacement and velocity in the antero-posterior and medio-lateral directions were also calculated. Intraclass correlation coefficients (ICCs) were used to determine test-retest reliability, and Bland-Altman plots were created to examine proportional biases.

RESULTS

ICC_3,2 were between 0.79 and 0.95 for all variables, indicating 'good' to 'excellent' reliability (>0.75). However, ICC_3,1 for symmetry indices and between-limb synchronization were < 0.75. Bland-Altman plots revealed possible proportional biases for root mean square of medio-lateral centre of pressure displacement and velocity and between-limb synchronization, with larger between-trial differences for participants with worse values.

SIGNIFICANCE

These findings suggest that centre of pressure measures extracted from a single 30-second quiet standing trial may have sufficient reliability for some research studies in chronic stroke. However, for clinical applications, the average of at least two trials may be required.

Age affects the relationships between kinematics and postural stability during gait

BACKGROUND

Past work has identified relationships between postural stability and joint kinematics during balance and sit-to-stand tasks. However, this work has not been extended to a thorough examination of these relationships during gait, and how these relationships change with age. An improved understanding of age-related changes in these relationships during gait is necessary to identify early predictors of gait impairments and implement targeted interventions to prevent functional decline in older adulthood.

RESEARCH QUESTION

How does age affect relationships between time-varying signals representing joint/segment kinematics and postural stability during gait?

METHODS

Three-dimensional, whole-body motion capture data from 48 participants (19 younger, 29 older) performing overground gait were used in this secondary analysis. Lower extremity joint angles, trunk segment angles, and margins of stability in the antero-posterior and mediolateral directions were subsequently derived. Pairings of angle and margin of stability signals were cross-correlated across the gait cycle. Metrics representing the strength of relationships were extracted from the cross-correlation functions and compared between groups.

RESULTS

At the ankle, significant age-related differences were only identified in the mediolateral direction, with older adults' coefficients being of greater magnitude and more tightly clustered, relative to younger adults. Differences were observed in both directions at the hip, with an overall trend of greater-magnitude and more tightly clustered coefficients among younger adults. For the trunk, the groups exhibited coefficients of opposite signs in the antero-posterior direction.

SIGNIFICANCE

While overall gait performance was similar between groups, age-related differences were identified in relationships between postural stability and kinematics, with stronger relationships at the hip and ankle for younger and older adults, respectively. Relationships between postural stability and kinematics may have potential as a marker for the early identification of gait impairment and/or dysfunction in older adulthood, and for quantifying the effectiveness of interventions to reduce gait impairment.

Quantifying Segmental Contributions to Center-of-Mass Motion During Dynamic Continuous Support Surface Perturbations Using Simplified Estimation Models

Investigating balance reactions following continuous, multidirectional, support surface perturbations is essential for improving our understanding of balance control in moving environments. Segmental motions are often incorporated into rapid balance reactions following external perturbations to balance, although the effects of these motions during complex, continuous perturbations have not been assessed. This study aimed to quantify the contributions of body segments (ie, trunk, head, upper extremity, and lower extremity) to the control of center-of-mass (COM) movement during continuous, multidirectional, support surface perturbations. Three-dimensional, whole-body kinematics were captured while 10 participants experienced 5 minutes of perturbations. Anteroposterior, mediolateral, and vertical COM position and velocity were calculated using a full-body model and 7 models with reduced numbers of segments, which were compared with the full-body model. With removal of body segments, errors relative to the full-body model increased, while relationship strength decreased. The inclusion of body segments appeared to affect COM measures, particularly COM velocity. Findings suggest that the body segments may provide a means of improving the control of COM motion, primarily its velocity, during continuous, multidirectional perturbations, and constitute a step toward improving our understanding of how the limbs contribute to balance control in moving environments.

Lower limb muscle activity underlying temporal gait asymmetry post-stroke

OBJECTIVE

Asymmetric walking after stroke is common, detrimental, and difficult to treat, but current knowledge of underlying physiological mechanisms is limited. This study investigated electromyographic (EMG) features of temporal gait asymmetry (TGA).

METHODS

Participants post-stroke with or without TGA and control adults (n = 27, 8, and 9, respectively) performed self-paced overground gait trials. EMG, force plate, and motion capture data were collected. Lower limb muscle activity was compared across groups and sides (more/less affected).

RESULTS

Significant group by side interaction effects were found: more affected plantarflexor stance activity ended early (p = .0006) and less affected dorsiflexor on/off time was delayed (p < .01) in persons with asymmetry compared to symmetric and normative controls. The TGA group exhibited fewer dorsiflexor bursts during swing (p = .0009).

CONCLUSIONS

Temporal patterns of muscular activation, particularly about the ankle around the stance-to-swing transition period, are associated with TGA. The results may reflect specific impairments or compensations that affect locomotor coordination.

SIGNIFICANCE

Neuromuscular underpinnings of spatiotemporal asymmetry have not been previously characterized. These novel findings may inform targeted therapeutic strategies to improve gait quality after stroke.

How does balance during functional tasks change across older adulthood?

BACKGROUND

Aging is associated with declining balance, which may increase fall risk and reduce independence. There is a paucity of work examining functional tasks (e.g., standing from a chair, lifting) related to fall risk. Additionally, many past studies have considered older adults as one age group, rather than viewing aging as a continuum across older adulthood.

RESEARCH QUESTION

How are age and balance measures related in healthy, independently-dwelling older adults during functional tasks?

METHODS

Thirty-eight older (60-89 years old) and 21 younger (18-30 years old) independently-dwelling adults performed quiet standing, sit-stand-sit, sit-stand-gait initiation, and lifting, while ground reaction forces and whole-body motion were measured. Variability of the net center of pressure displacement (root-mean-square; antero-posterior and mediolateral), and minimum margin of stability (anterior, posterior, mediolateral, and/or medial and lateral) were extracted. Regression analyses were used to identify relationships with age for both the full participant sample and the older adult cohort, accounting for sex and task characteristics.

RESULTS

Age was significantly related to balance measures for both participant samples; net center of pressure root-mean-square and minimum margin of stability tended to increase and decrease with age, respectively. For older adults, significant relationships were primarily in the antero-posterior and mediolateral directions for sit-stand-gait initiation and sit-stand-sit, respectively. Relationships did not appear to be simply a function of differences in task performance with age.

SIGNIFICANCE

Some evidence of balance declines during functional tasks was observed across older adulthood, including declines that did not appear in the full participant sample. However, further work with a more diverse older adult cohort will be required to confirm these results. Findings may contribute to the development of strategies for improving balance control and reducing fall risk in older adults, by identifying the balance measures most likely to decline across older adulthood as potential target tasks for interventions.

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

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

Interaction Between Thoracic Movement and Lumbar Spine Muscle Activation Patterns in Young Adults Asymptomatic for Low Back Pain: A Cross-Sectional Study

OBJECTIVE

The purpose of this study was to investigate the interaction between thoracic movement and lumbar muscle co-contraction when the lumbar spine was held in a relatively neutral posture.

METHODS

Thirty young adults, asymptomatic for back pain, performed 10 trials of upright standing, maximum trunk range of motion, and thoracic movement tasks while lumbar muscle activation was measured. Lumbar co-contraction was calculated, compared between tasks, and correlated to thoracic angles.

RESULTS

Movement tasks typically exhibited greater co-contraction than upright standing. Co-contraction in the lumbar musculature was 67%, 45%, and 55% greater than upright standing for thoracic flex, thoracic bend, and thoracic twist, respectively. Generally, the thoracic movement task demonstrated greater co-contraction than the maximum task in the same direction. Co-contraction was also correlated to thoracic angles in each movement direction.

CONCLUSION

Tasks with thoracic movement and a neutral lumbar spine posture resulted in increases in co-contraction within the lumbar musculature compared with quiet standing and maximum trunk range-of-motion tasks. Findings indicated an interaction between the 2 spine regions, suggesting that thoracic posture should be accounted for during the investigation of lumbar spine mechanics.

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

BACKGROUND

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

RESEARCH QUESTION

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

METHODS

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

RESULTS

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

SIGNIFICANCE

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

Does Perturbation-Based Balance Training Improve Control of Reactive Stepping in Individuals with Chronic Stroke?

BACKGROUND

Although perturbation-based balance training (PBT) may be effective in improving reactive balance control and/or reducing fall risk in individuals with stroke, the characteristics of reactive balance responses that improve following PBT have not yet been identified. This study aimed to determine if reactive stepping characteristics and timing in response to support-surface perturbations improved to a greater extent following PBT, compared to traditional balance training.

MATERIALS AND METHODS

This study represents a substudy of a multisite randomized controlled trial. Sixteen individuals with chronic stroke were randomly assigned to either perturbation-based or traditional balance training, and underwent 6-weeks of training as a part of the randomized controlled trial. Responses to support-surface perturbation were evaluated pre- and post-training, and 6-months post-training. Reactive stepping characteristics and timing were compared between sessions within each group, and between groups at post-training and 6-months post-training while controlling for each measure at the pre-training session.

RESULTS

The frequency of extra steps in response to perturbations decreased from pre-training to post-training for the PBT group, but not for the control group.

CONCLUSIONS

Improvements in reactive balance control were identified after PBT in individuals with chronic stroke. Findings provide insight into the mechanism by which PBT improves reactive balance control poststroke, and support the use of PBT in balance rehabilitation programs poststroke.

Does perturbation-based balance training prevent falls among individuals with chronic stroke? A randomised controlled trial

OBJECTIVES

No intervention has been shown to prevent falls poststroke. We aimed to determine if perturbation-based balance training (PBT) can reduce falls in daily life among individuals with chronic stroke.

DESIGN

Assessor-blinded randomised controlled trial.

SETTING

Two academic hospitals in an urban area.

INTERVENTIONS

Participants were allocated using stratified blocked randomisation to either 'traditional' balance training (control) or PBT. PBT focused on improving responses to instability, whereas traditional balance training focused on maintaining stability during functional tasks. Training sessions were 1 hour twice/week for 6 weeks. Participants were also invited to complete 2 'booster' training sessions during the follow-up.

PARTICIPANTS

Eighty-eight participants with chronic stroke (>6 months poststroke) were recruited and randomly allocated one of the two interventions. Five participants withdrew; 42 (control) and 41 (PBT group) were included in the analysis.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome was rate of falls in the 12 months post-training. Negative binomial regression was used to compare fall rates between groups. Secondary outcomes were measures of balance, mobility, balance confidence, physical activity and social integration.

RESULTS

PBT participants reported 53 falls (1.45 falls/person-year) and control participants reported 64 falls (1.72 falls/person-year; rate ratio: 0.85(0.42 to 1.69); p=0.63). Per-protocol analysis included 32 PBT and 34 control participants who completed at least 10/12 initial training sessions and 1 booster session. Within this subset, PBT participants reported 32 falls (1.07 falls/person-year) and control participants reported 57 falls (1.75 falls/person-year; rate ratio: 0.62(0.29 to 1.30); p=0.20). PBT participants had greater improvement in reactive balance control than the control group, and these improvements were sustained 12 months post-training. There were no intervention-related serious adverse effects.

CONCLUSIONS

The results are inconclusive. PBT may help to prevent falls in daily life poststroke, but ongoing training may be required to maintain the benefits.

TRIAL REGISTRATION NUMBER

ISRCTN05434601; Results.

Characterization of Reactions to Laterally Directed Perturbations in People With Chronic Stroke

BACKGROUND

Reactive balance control is often impaired poststroke. Studies addressing responses to laterally directed perturbations in this population are currently lacking. Given that stroke-related motor impairments are unilateral, a better understanding of reactive balance responses to these types of perturbations is critical.

OBJECTIVE

This study aimed to quantify differences in reactive balance control in response to laterally directed perturbations in people with chronic stroke, based on perturbation direction and ability to step with either limb.

DESIGN

This study used a cross-sectional design.

METHODS

Participants with chronic stroke (N = 19) were divided into groups representing their ability to step with either limb, based on performance on a reactive balance task in a baseline assessment. The preferred stepping limb was also identified during this assessment. Each participant then underwent a series of laterally directed perturbations on a motion platform. Behavioral measures were compared between platform direction and group.

RESULTS

Trials with extra steps, step initiation with the preferred limb, and crossover steps were more common with platform motion toward the preferred limb compared to the nonpreferred limb; the latter effect was only observed for participants with an impaired ability to step with either limb. Side-step sequences were more common in those able to step with either limb when the platform moved toward the preferred limb.

LIMITATIONS

The participant sample was likely higher functioning than the general population of stroke survivors due to equipment constraints. Additionally, participants may have developed strategies to use the platform's motion characteristics to aid with balance recovery.

CONCLUSIONS

These findings provide an indication of responses to laterally directed perturbations in people with chronic stroke and may help inform strategies for improving reactive balance control during stroke rehabilitation.

Exploring the relationship between stability and variability of the centre of mass and centre of pressure

BACKGROUND

There are competing perspectives in the literature regarding the role of movement variability in quiet standing and balance control. Some view high variability as indicative of poor balance control and a contributor to increased fall risk, whereas others view variability as beneficial in providing sensory information that aids balance control.

RESEARCH QUESTION

This study aimed to help to clarify the role of variability in balance control by testing two competing hypotheses: that increased variability would lead to instability, or that increased variability would improve stability, where stability is defined as the ability to respond to a perturbation.

METHODS

Fourteen healthy young adults (20-35 years old) were recruited. Participants experienced postural perturbations of varying magnitudes, delivered via sudden backward movement of the support surface. Magnitudes of postural perturbation were chosen such that both step and no-step responses could be observed at each magnitude. Variability in the centre of mass and centre of pressure movement was measured for 10 s prior to the postural perturbation. Multiple regression was used to determine if movement variability predicted step responses when controlling for perturbation magnitude, trial order, and margin of stability at perturbation onset.

RESULTS

Lower variability in medio-lateral centre of mass and centre of pressure position, and lower variability in medio-lateral centre of pressure velocity were related to increased odds of stepping in response to the perturbation (p-values ≤0.001).

SIGNIFICANCE

This study provides support for the hypothesis that, at least for relatively low variability values, increased centre of pressure and mass movement variability improves stability. Specifically, increasing movement of the centre of pressure and mass in the medio-lateral direction may help to preserve stability in the antero-posterior direction by providing the central nervous system with information about the antero-posterior centre of mass across a wide range of medio-lateral positions.

Relationship between margin of stability and deviations in spatiotemporal gait features in healthy young adults

Increased variability of spatio-temporal features while walking is related to increased risk of falls. It is thought that variability in foot placement and timing reflects responses to mechanical instability while walking. The purpose of this study was to determine whether 'extreme' values of step length, width and time follow transient periods of low mechanical stability during the single support phase of gait in healthy young adults. We conducted secondary analysis of a portion of an existing dataset. Eleven healthy adults walked on an instrumented treadmill. Participants were outfitted with reflective markers and completed two 1-min periods of walking at each of 3 speeds (0.8m/s, 1.2m/s, and 1.6m/s). Margins of stability were calculated relative to the anterior, posterior, lateral, and medial boundaries of the base of support, and the value at heel strike and the minimum value during the first half of each single-support phase were extracted. Step length, swing time, and step width were calculated from motion capture and ground reaction force data. Extreme values for consecutive steps were identified using Poincaré plots, and margins of stability in each direction were compared between 'normal' and 'extreme' steps. Margins of stability in both the anterior and medial direction were lower prior to long and wide steps, respectively. Margins of stability in the anterior and medial directions were lower prior to quick steps, and margins of stability in the posterior and lateral directions were lower prior to slow steps. There were either no significant differences in margin of stability between 'normal' and 'extreme' steps at heel strike, or the direction of the relationship was reversed to that observed during single support. These data suggest that spatio-temporal variability may reflect adjustments in step placement and timing to compensate for transient periods of low mechanical stability when walking.

Factors Contributing to Unexpected Retirement and Unemployment in Adults Over 50 Years Old in Ireland

Older adults are increasingly important to maintaining stable workforces. As such, factors contributing to early workforce exit must be identified. This study aimed to identify predictors of unexpected retirement and unemployment at older age, with respect to psychological constructs, resulting adverse behaviors, and health-related factors reflecting functional status. Data were extracted from The Irish Longitudinal Study on Ageing (TILDA) to predict unexpected retirement and unemployment in older adults in Ireland. Increasing age, increasing number of impairments in activities of daily living, and frailty status of “pre-frail/frail” (relative to non-frail) increased the likelihood of unexpected retirement; while greater numbers of physical limitations and “pre-frail/frail” status significantly predicted unemployment at older age. Pre-frail/frail status or reduced physical capability for everyday tasks may adversely affect older individuals’ ability to obtain and/or maintain employment. These findings advance the current understanding of factors associated with unexpected retirement and unemployment at older ages. Findings may aid in identifying strategies to extend working life and to aid at-risk older adults, and may inform components of care on which to focus to minimize loss of function and mobility, and maintain independence, with aging.

Does Perturbation Training Prevent Falls after Discharge from Stroke Rehabilitation? A Prospective Cohort Study with Historical Control

BACKGROUND

Individuals with stroke fall frequently, and no exercise intervention has been shown to prevent falls post stroke. Perturbation-based balance training (PBT), which involves practicing reactions to instability, shows promise for preventing falls in older adults and individuals with Parkinson's disease. This study aimed to determine if PBT during inpatient stroke rehabilitation can prevent falls after discharge into the community.

METHODS

Individuals with subacute stroke completed PBT as part of routine inpatient rehabilitation (n = 31). Participants reported falls experienced in daily life for up to 6 months post discharge. Fall rates were compared to a matched historical control group (HIS) who did not complete PBT during inpatient rehabilitation.

RESULTS

Five of 31 PBT participants, compared to 15 of 31 HIS participants, reported at least 1 fall. PBT participants reported 10 falls (.84 falls per person per year) whereas HIS participants reported 31 falls (2.0 falls per person per year). When controlled for follow-up duration and motor impairment, fall rates were lower in the PBT group than the HIS group (rate ratio: .36 [.15, .79]; P = .016).

CONCLUSIONS

These findings suggest that PBT is promising for reducing falls post stroke. While this was not a randomized controlled trial, this study may provide sufficient evidence for implementing PBT in stroke rehabilitation practice.

Atypical anticipatory postural adjustments during gait initiation among individuals with sub-acute stroke

Anticipatory postural adjustments, executed prior to gait initiation, help preserve lateral stability when stepping. Atypical patterns of anticipatory activity prior to gait initiation may occur in individuals with unilateral impairment (e.g., stroke). This study aimed to determine the prevalence, correlates, and consequences of atypical anticipatory postural adjustment patterns prior to gait initiation in a sub-acute stroke population. Forty independently-ambulatory individuals with sub-acute stroke stood on two force plates and initiated gait at a self-selected speed. Medio-lateral centre of pressure displacement was calculated and used to define anticipatory postural adjustments (shift in medio-lateral centre of pressure >10mm from baseline). Stroke severity, motor recovery, and functional balance and mobility status were also obtained. Three patterns were identified: single (typical), absent (atypical), and multiple (atypical) anticipatory postural adjustments. Thirty-five percent of trials had atypical anticipatory postural adjustments (absent and multiple). Frequency of absent anticipatory postural adjustments was negatively correlated with walking speed. Multiple anticipatory postural adjustments were more prevalent when leading with the non-paretic than the paretic limb. Trials with multiple anticipatory postural adjustments had longer duration of anticipatory postural adjustment and time to foot-off, and shorter unloading time than trials with single anticipatory postural adjustments. A high prevalence of atypical anticipatory control prior to gait initiation was found in individuals with stroke. Temporal differences were identified with multiple anticipatory postural adjustments, indicating altered gait initiation. These findings provide insight into postural control during gait initiation in individuals with sub-acute stroke, and may inform interventions to improve ambulation in this population.

Balance Confidence Is Related to Features of Balance and Gait in Individuals with Chronic Stroke

BACKGROUND

Reduced balance confidence is associated with impairments in features of balance and gait in individuals with subacute stroke. However, an understanding of these relationships in individuals at the chronic stage of stroke recovery is lacking. This study aimed to quantify the relationships between balance confidence and specific features of balance and gait in individuals with chronic stroke.

METHODS

Participants completed a balance confidence questionnaire and clinical balance assessment (quiet standing, walking, and reactive stepping) at 6 months postdischarge from inpatient stroke rehabilitation. Regression analyses were performed using balance confidence as a predictor variable, and quiet standing, walking, and reactive stepping outcome measures as the dependent variables.

RESULTS

Walking velocity was positively correlated with balance confidence, whereas mediolateral center of pressure excursion (quiet standing) and double support time, step width variability, and step time variability (walking) were negatively correlated with balance confidence.

CONCLUSIONS

This study provides insight into the relationships between balance confidence and balance and gait measures in individuals with chronic stroke, suggesting that individuals with low balance confidence exhibited impaired control of quiet standing as well as walking characteristics associated with cautious gait strategies. Future work should identify the direction of these relationships to inform community-based stroke rehabilitation programs for individuals with chronic stroke, and determine the potential utility of incorporating interventions to improve balance confidence into these programs.

Breast size impacts spine motion and postural muscle activation

BACKGROUND

While it is generally accepted that large breast sizes in females contribute to back pain and poor posture, the effects of breast size on spinal motion and muscle activation characteristics are poorly understood.

OBJECTIVE

This study examined the relationship between breast size, spine motion, and trunk muscle activation.

METHODS

Fifteen university-aged females, free of back pain symptoms, were tested. Breast sizes were calculated, and three-dimensional spine motion and activation from five trunk muscles bilaterally were measured during standing and trunk flexion movements. Correlations between breast size and motion and muscle activation measures were assessed.

RESULTS

Head and trunk angles were strongly, negatively correlated to breast size during upright standing; thoracic angles were moderately, positively correlated to breast size during thoracic flexion movements. Trunk muscles showed positive, moderate-strength relationships with breast size during upright standing and some trunk movements.

CONCLUSIONS

These findings provide a preliminary indication that increasing breast sizes are associated with altered postures and increased muscle activation in a non-clinical population, and constitute a baseline for the study of females with a full range of breast sizes. Further research is required to confirm the generalizability of these findings to other sizes, in order to inform strategies for the prevention or reduction of back pain, as well as diagnosis, treatment, and rehabilitation techniques associated with breast size and back pain.

Timing of reactive stepping among individuals with sub-acute stroke: effects of 'single-task' and 'dual-task' conditions

Performance decrements in balance tasks are often observed when a secondary cognitive task is performed simultaneously. This study aimed to determine whether increased cognitive load resulted in altered reactive stepping in individuals with sub-acute stroke, compared to a reactive stepping trial with no secondary task. The secondary purpose was to determine whether differences existed between the first usual-response trial, subsequent usual-response trials, and the dual-task condition. Individuals with sub-acute stroke were exposed to external perturbations to elicit reactive steps. Perturbations were performed under a usual-response (single-task) and dual-task condition. Measures of step timing and number of steps were based on force plate and video data, respectively; these measures were compared between the usual-response and dual-task trials, and between the first usual-response trial, later usual-response trials (trials 2-5) and a dual-task trial. A longer time of unloading onset and greater number of steps were identified for the first usual-response trial compared to later usual-response trials. No significant differences were identified between usual-response and dual-task trials. Although improvements were observed from the first to subsequent usual-response lean-and-release trials, performance then tended to decrease with the introduction of the dual-task condition. These findings suggest that when introduced after usual-response trials, the dual-task trial may represent the first trial of a new condition, which may be beneficial in reducing the potential for adaptation that may occur after multiple repetitions of a reactive stepping task. Therefore, these findings may lend support to the introduction of a new condition (i.e. a dual-task trial) in addition to usual-response trials when assessing reactive balance in individuals with stroke.

Seated maximum flexion: An alternative to standing maximum flexion for determining presence of flexion-relaxation?

BACKGROUND

The flexion-relaxation phenomenon (FRP) in standing is a specific and sensitive diagnostic tool for low back pain. Seated flexion as an alternative could be beneficial for certain populations, yet the behavior of the trunk extensors during seated maximum flexion compared to standing flexion remains unclear.

OBJECTIVE

Compare FRP occurrences and spine angles between seated and standing flexion postures in three levels of the erector spinae muscles.

METHODS

Thirty-one participants free of back pain performed seated and standing maximum trunk flexion. Electromyographical signals were recorded from the bilateral lumbar (L3), lower-thoracic (T9), and upper-thoracic (T4) erector spinae and assessed for the occurrence of FRP. Spine angles corresponding to FRP onset and cessation were determined, and FRP occurrences and angles were compared between posture and muscle.

RESULTS

FRP occurrence was similar in standing and seated maximum flexion across all muscles, with the lumbar muscles showing the greatest consistency. Standing FRP onset and cessation angles were consistently greater than the corresponding seated FRP angles.

CONCLUSION

Considering the similar number of FRP occurrences, seated maximum flexion may constitute an objective criterion for low back pain diagnosis. Future work should seek to confirm the utility of this test in individuals with low back pain.

Do quiet standing centre of pressure measures within specific frequencies differ based on ability to recover balance in individuals with stroke?

OBJECTIVE

To determine whether quiet standing measures at specific frequency levels (representative of reactive control) differed between individuals with stroke based on their ability to recover balance (Failed or Successful Responses to external perturbations).

METHODS

Individuals with stroke completed a clinical assessment, including 30 s of quiet standing and lean-and-release postural perturbations, at admission to in-patient rehabilitation. Quiet standing centre of pressure (COP) signals were calculated and discrete wavelet decomposition was performed. Net COP amplitude, between-limb synchronization, and ratios of individual-limb COP were determined for each frequency level of interest, and for the non-decomposed signal (all frequency levels). Outcome measures were compared between individuals who exhibited Failed and Successful Responses during (a) unconstrained and (b) encouraged-use lean-and-release trials.

RESULTS

Individuals with Failed Responses during the unconstrained lean-and-release trials displayed greater net COP amplitude than those with Successful Responses, specifically within a frequency range of 0.40-3.20Hz.

CONCLUSIONS

Reduced ability to recover balance among individuals with stroke may be reflected in impaired reactive control of quiet standing.

SIGNIFICANCE

These results provide insight into the mechanism by which reactive control of quiet standing is impaired in individuals with stroke, and may inform assessment and rehabilitation strategies for post-stroke reactive balance control.

Relationships between fear of falling, balance confidence, and control of balance, gait, and reactive stepping in individuals with sub-acute stroke

Fear of falling is common in individuals with stroke; however, the associations between fear of falling, balance confidence, and the control of balance and gait are not well understood for this population. This study aimed to determine whether, at the time of admission to in-patient rehabilitation, specific features of balance and gait differed between individuals with stroke who did and did not report fear of falling, and whether these features were related to balance confidence. Individuals with stroke entering in-patient rehabilitation were asked if they were afraid of falling, and completed the Activities-Specific Balance Confidence Scale. Participants performed quiet standing, gait, and reactive stepping tasks, and specific measures were extracted for each (quiet standing: centre of pressure amplitude, between-limb synchronization, and Romberg quotients; gait: walking velocity, double support time, and variability measures; reactive stepping: number of steps, frequency of grasp reactions, and frequency of assists). No significant differences were identified between individuals with and without fear of falling. Balance confidence was negatively related to centre of pressure amplitude, double support time, and step time variability, and positively related to walking velocity. Low balance confidence was related to poor quiet standing balance control and cautious behavior when walking in individuals with sub-acute stroke. While the causal relationship between balance confidence and the control of balance and gait is unclear from the current work, these findings suggest there may be a role for interventions to increase balance confidence among individuals with stroke, in order to improve functional mobility.

Perturbation training to promote safe independent mobility post-stroke: study protocol for a randomized controlled trial

Background

Falls are one of the most common medical complications post-stroke. Physical exercise, particularly exercise that challenges balance, reduces the risk of falls among healthy and frail older adults. However, exercise has not proven effective for preventing falls post-stroke. Falls ultimately occur when an individual fails to recover from a loss of balance. Thus, training to specifically improve reactive balance control could prevent falls. Perturbation training aims to improve reactive balance control by repeatedly exposing participants to postural perturbations. There is emerging evidence that perturbation training reduces fall rates among individuals with neurological conditions, such as Parkinson disease. The primary aim of this work is to determine if perturbation-based balance training can reduce occurrence of falls in daily life among individuals with chronic stroke. Secondary objectives are to determine the effect of perturbation training on balance confidence and activity restriction, and functional balance and mobility.

Methods/design

Individuals with chronic stroke will be recruited. Participants will be randomly assigned to one of two groups: 1) perturbation training, or 2) ‘traditional’ balance training. Perturbation training will involve both manual perturbations (e.g., a push or pull from a physiotherapist), and rapid voluntary movements to cause a loss of balance. Training will occur twice per week for 6 weeks. Participants will record falls and activity for 12 months following completion of the training program. Standardized clinical tools will be used to assess functional balance and mobility, and balance confidence before and after training.

Discussion

Falls are a significant problem for those with stroke. Despite the large body of work demonstrating effective interventions, such as exercise, for preventing falls in other populations, there is little evidence for interventions that prevent falls post-stroke. The proposed study will investigate a novel and promising intervention: perturbation training. If effective, this training has the potential to not only prevent falls, but to also improve safe independent mobility and engagement in daily activities for those with stroke.

Trial registration

Current Controlled Trials: ISRCTN05434601.

Repeatability of kinematic and electromyographical measures during standing and trunk motion: how many trials are sufficient?

Previous studies have recommended a minimum of five trials to produce repeatable kinematic and electromyography (EMG) measures during target postures or contraction levels. This study aimed to evaluate the repeatability and reliability of kinematic and EMG measures that are of primary interest in the investigation of trunk movement, and to determine the number of trials required to achieve repeatability and reliability for these measures. Thirty participants performed ten trials of upright standing and maximum trunk ranges-of-motion. Mean (upright standing) and maximum (movement tasks) kinematic and EMG measures were assessed using intraclass correlation coefficients and standard error of measurement, which were used to identify the minimum number of trials for each measure. The repeatability and reliability of the measures were generally high, with 64%, 77%, 85%, and 92% of measures producing repeatable and reliable values with two, three, four, and five trials, respectively. Ten trials were not sufficient for several upright standing angle measures and maximum twist lumbar angles. Further, several abdominal muscles during maximum flexion, as well as the left lower-thoracic erector spinae during maximum twist, required as many as five trials. These measures were typically those with very small amounts of motion, or muscles that did not act in the role of prime mover. These results suggest that as few as two trials may be sufficient for many of the kinematic and EMG measures of primary interest in the investigation of trunk movement, while the collection of four trials should produce repeatable and reliable values for over 80% of measures. These recommendations are intended to provide an acceptable trade-off between repeatable and reliable values and feasibility of the collection protocol.

Quantification of the lumbar flexion-relaxation phenomenon: comparing outcomes of lumbar erector spinae and superficial lumbar multifidus in standing full trunk flexion and slumped sitting postures

OBJECTIVE

The purpose of this study was to identify differences in flexion-relaxation outcomes in asymptomatic participants, with respect to both flexion-relaxation phenomenon (FRP) occurrence and spinal onset angles, as a function of posture and choice of muscle being examined.

METHODS

This was a cross-sectional study in a laboratory setting. Thirty asymptomatic participants performed standing full trunk flexion and slumped sitting postures while activation levels of the lumbar erector spinae and superficial lumbar multifidus were monitored. Two thresholds were used to define whether FRP was present in each muscle and, if present, at what trunk flexion angle it occurred. These outcomes were compared descriptively between muscles and between postures.

RESULTS

Most participants displayed FRP in both muscles during standing full flexion; occurrences were more variable in slumped sitting. On average, FRP during standing full flexion and slumped sitting occurred at approximately 80% and 52% of participants' maximum flexion value, respectively. Variability in the slumped sitting onset angles was greater than that in standing full flexion.

CONCLUSION

Outcomes for FRP during standing full flexion in asymptomatic participants appeared to be more robust and were not affected by the choice of either lumbar erector spinae or superficial lumbar multifidus. Conversely, during slumped sitting, FRP occurrence varied substantially depending on choice of muscle, although onset angles were relatively consistent between muscles. Although the choice of one muscle over the other may be warranted, it may be prudent to examine both muscles during FRP investigations in sitting postures, in order to fully characterize the behavior and activation patterns of the lumbar musculature.

Differences in distal lower extremity tissue masses and mass ratios exist in athletes of sports involving repetitive impacts

This study aimed to examine the effects of sex and sport on the tissue composition of the distal lower extremity of varsity athletes, in sports that involve repetitive-impact loading patterns. Fat mass, lean mass, bone mineral content and wobbling mass were predicted for the leg and leg + foot segments of varsity basketball, cross-country, soccer and volleyball athletes. The absolute masses were normalised to body mass, and also expressed relative to each other as ratios. Females and males differed on most normalised tissue masses and ratios by 11-101%. Characteristic differences were found in the normalised tissue masses across sports, with the lowest and highest values displayed by cross-country and volleyball (female)/basketball (male) athletes, respectively. Conversely, cross-country athletes had the highest wobbling mass:bone mineral content and lean mass:bone mineral content ratios for females by 10% and 16%, respectively. The differences between sports may be explained in part by different impact loading patterns characteristic of each sport. Tissue mass ratio differences between sports may suggest that the ratios of soft to rigid tissues are optimised by the body in response to typical loading patterns, and may therefore be useful in investigations of distal lower extremity injury mechanisms in athletes.

Evaluation of methods for the quantification of the flexion-relaxation phenomenon in the lumbar erector spinae muscles

OBJECTIVES

There are various methods to quantify the flexion-relaxation phenomenon (FRP); however, there is little standardization. This study aimed to evaluate the performance of various quantification methods in terms of their ability to identify lumbar erector spinae flexion-relaxation during standing forward trunk flexion.

METHODS

The study was a cross-sectional design in a laboratory setting. Lumbar erector spinae activation levels were measured in 12 male participants performing full trunk flexion movements. Electromyographical signals were assessed using 16 criteria within 4 quantification methods (visual, statistical, threshold, ratio), and the sensitivity of each was assessed relative to the benchmark criterion (visual inspection of raw electromyography data).

RESULTS

Visual inspection and most of the threshold and ratio criteria displayed the highest sensitivity. On average (SD) across the 16 criteria, FRP was positively identified 21.6 (6.2) times of 24 data sets (12 participants, 2 muscles). The visual inspection criteria positively identified FRP in all 24 trials, whereas the statistical method did not identify FRP at all (P = .44 and P = .46 for the left and right sides, respectively). The threshold and ratio criteria positively identified FRP 23.2 (1.5) and 22.5 (3.7) times, on average, respectively. Results from criteria based on differences between upright and fully flexed muscle activation tended to be conservative in FRP identification. The methods were classified as reliable or nonreliable, based on their sensitivity when specific characteristics were evident in the electromyography signals.

CONCLUSIONS

Although many of the criteria identified FRP with 100% sensitivity, others produced unrealistic results. The latter may be suitable for other experimental designs or may require reevaluation regarding their ability to identify FRP. Although visual inspection, threshold, or ratio methods performed well and may be appropriate for either biomechanical or clinical research, the threshold method provided the optimal trade-off between performance, consistency, and feasibility for these data.

Investigation of trunk muscle co-contraction and its association with low back pain development during prolonged sitting

Previous work has shown muscle activation differences between chronic low back pain patients and healthy controls in sitting postures, and between asymptomatic individuals who do (PDs: pain developers) and do not (NPDs: non-pain developers) develop transient back pain during prolonged standing (as determined using a visual analog scale). The current study aimed to investigate differences in trunk muscle co-contraction between PD and NPD individuals over 2h of prolonged sitting. Ten healthy males sat continuously for 2h while performing tasks that simulated computer-aided-drafting; four were classified as PDs, and six as NPDs. Co-contraction indices were calculated from EMG data collected from eight trunk muscles bilaterally, and compared between pain groups and over time. PDs exhibited higher levels of co-contraction than NPDs. Additionally, co-contraction tended to increase over time, and was significantly correlated to pain development. The relationship between co-contraction and back pain development may actually be circular, in that it is both causal and adaptive: high co-contraction initially predisposes to pain development, following which co-contraction further increases in an attempt to alleviate the pain, and the cycle perpetuates. Further work will be required to elucidate the exact nature of this relationship, and to confirm the generalizability to other populations.

Tissue mass ratios and the reporting of distal lower extremity injuries in varsity athletes at a Canadian University

The purpose of this preliminary investigation was to determine the relative role of the distal lower extremity tissue masses of varsity athletes in predicting distal lower extremity injury sustained during a competitive season. One hundred male and female varsity athletes (basketball, volleyball, soccer, cross country) completed a questionnaire on general health, physiological, and psychosocial variables, during each sport's respective training camp. A series of anthropometric measurements were used as inputs to distal lower extremity tissue mass prediction equations to calculate lean mass, fat mass, bone mineral content and wobbling mass (lean mass + fat mass) and tissue mass ratios. Athletes were monitored throughout their respective seasons and were instructed to report any distal lower extremity injuries to a certified athletic therapist who was responsible for assessing and confirming the reports. Logistic regression analyses were performed to determine which variables significantly predicted distal lower extremity injury. Mean leg fat mass:bone mass (OR = 1.6, CI = 1.0 - 2.5), and competition surface (rubber OR = 8.5, CI = 1.5 - 47.7; artificial turf OR = 4.0, CI = 0.77 - 22.9) were identified as significant predictors of injury. Overall, tibia bone injuries were significantly associated with the ratio of fat mass:bone mineral content and the surface on which the athletes compete.