The impact of walking speed on interlimb coordination in individuals with Parkinson's disease.

[Purpose] Interlimb coordination can be affected by the symptoms associated with Parkinson's disease and may result in an increased risk of falls. The purpose of the current study was to compare changes in interlimb coordination in individuals with Parkinson's disease to healthy older adults while systematically manipulating walking speed. [Subjects and Methods] Participants walked on a treadmill while systematically increasing and decreasing the walking speed between 0.22 and 1.30 m/s. Kinematic data were collected by means of a three dimensional motion capture system. Dependent variables included the phase relation between arm and leg movements as well as between pelvic and thoracic rotation. [Results] Compared to healthy controls, an increased variability in relative phase between left and right arm swing, and smaller amplitude with arm, leg as well as less variability for the phase relation between thoracic and pelvic rotations were shown in individuals with Parkinson's disease. [Conclusion] The increased variability of phase relation between left and right arm swing may be related to the reduced out-of-phase forcing of the arm movements at the shoulders as a result of axial rigidity in Parkinson's disease. It deserves further investigation whether the improvement of the coordination between arms could result in the normalization of parkinsonian gait.

Musculoskeletal stiffness changes linearly in response to increasing load during walking gait.

Development of biologically inspired exoskeletons to assist soldiers in carrying load is a rapidly expanding field. Understanding how the body modulates stiffness in response to changing loads may inform the development of these exoskeletons and is the purpose of the present study. Seventeen subjects walked on a treadmill at a constant preferred walking velocity while nine different backpack loading conditions ranging from 12.5% to 40% bodyweight (BW) were introduced in an ascending and then descending order. Kinematic data were collected using Optotrak, a 3D motion analysis system, and used to estimate the position of the center of mass (COM). Two different estimates of stiffness were computed for the stance phase of gait. Both measures of stiffness were positively and linearly related to load magnitudes, with the slopes of the relationships being larger for the descending than the ascending conditions. These results indicate that changes in mechanical stiffness brought about in the musculoskeletal system vary systematically during increases in load to ensure that critical kinematic variables measured in a previous publication remain invariant (Caron et al., 2013). Changes in stiffness and other kinematics measured at the 40% BW condition suggest a boundary in which gait stiffness control limit is reached and a new gait pattern is required. Since soldiers are now carrying up to 96% of body weight, the need for research with even heavier loads is warranted. These findings have implications on the development of exoskeletons to assist in carrying loads.

Computer-adaptive balance testing improves discrimination between community-dwelling elderly fallers and nonfallers.

OBJECTIVES: To build an item response theory-based computer adaptive test (CAT) for balance from 3 traditional, fixed-form balance measures: Berg Balance Scale (BBS), Performance-Oriented Mobility Assessment (POMA), and dynamic gait index (DGI); and to examine whether the CAT's psychometric performance exceeded that of individual measures. DESIGN: Secondary analysis combining 2 existing datasets. SETTING: Community based. PARTICIPANTS: Community-dwelling older adults (N=187) who were aged ≥65 years (mean age, 75.2±6.8y, 69% women). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The BBS, POMA, and DGI items were compiled into an initial 38-item bank. The Rasch partial credit model was used for final item bank calibration. CAT simulations were conducted to identify the ideal CAT. CAT score accuracy, reliability, floor and ceiling effects, and validity were examined. Floor and ceiling effects and validity of the CAT and individual measures were compared. RESULTS: A 23-item bank met model expectations. A 10-item CAT was selected, showing a very strong association with full item bank scores (r=.97) and good overall reliability (.78). Reliability was better in low- to midbalance ranges as a result of better item targeting to balance ability when compared with the highest balance ranges. No floor effect was noted. The CAT ceiling effect (11.2%) was significantly lower than the POMA (40.1%) and DGI (40.3%) ceiling effects (P<.001 per comparison). The CAT outperformed individual measures, being the only test to discriminate between fallers and nonfallers (P=.007), and being the strongest predictor of self-reported function. CONCLUSIONS: The balance CAT showed excellent accuracy, good overall reliability, and excellent validity compared with individual measures, being the only measure to discriminate between fallers and nonfallers. Prospective examination, particularly in low-functioning older adults and clinical populations with balance deficits, is recommended. Development of an improved CAT based on an expanded item bank containing higher difficulty items is also recommended.

Effects of Parkinson's disease on optic flow perception for heading direction during navigation.

Visuoperceptual disorders have been identified in individuals with Parkinson's disease (PD) and may affect the perception of optic flow for heading direction during navigation. Studies in healthy subjects have confirmed that heading direction can be determined by equalizing the optic flow speed (OS) between visual fields. The present study investigated the effects of PD on the use of optic flow for heading direction, walking parameters, and interlimb coordination during navigation, examining the contributions of OS and spatial frequency (dot density). Twelve individuals with PD without dementia, 18 age-matched normal control adults (NC), and 23 young control adults (YC) walked through a virtual hallway at about 0.8 m/s. The hallway was created by random dots on side walls. Three levels of OS (0.8, 1.2, and 1.8 m/s) and dot density (1, 2, and 3 dots/m(2)) were presented on one wall while on the other wall, OS and dot density were fixed at 0.8 m/s and 3 dots/m(2), respectively. Three-dimensional kinematic data were collected, and lateral drift, walking speed, stride frequency and length, and frequency, and phase relations between arms and legs were calculated. A significant linear effect was observed on lateral drift to the wall with lower OS for YC and NC, but not for PD. Compared to YC and NC, PD veered more to the left under OS and dot density conditions. The results suggest that healthy adults perceive optic flow for heading direction. Heading direction in PD may be more affected by the asymmetry of dopamine levels between the hemispheres and by motor lateralization as indexed by handedness.

Effect of body-scaled information on reaching in children with hemiplegic cerebral palsy: a pilot study.

PURPOSE: This study examined body-scaled information that specifies the reach patterns of children with hemiplegic cerebral palsy and children with typical development. METHODS: Nine children with hemiplegic cerebral palsy (3-5 years) and 9 age-matched children with typical development participated in the study. They were required to reach and grasp 10 different pairs of cubes. Reach data were coded as either a 1-handed reach or a 2-handed reach. Dimensionless ratios were calculated by dividing the cube size by the maximal aperture between the index finger and thumb. A critical ratio was used to establish the shift from a 1-handed to an exclusive 2-handed reach. RESULTS: The critical ratio was not significantly different for either preferred or nonpreferred arms within and between groups. All children used an exclusive 2-handed reach at a similar dimensionless ratio. CONCLUSION: Our study provides evidence of the "fit" between environment (cube size) and the individual's capabilities (finger aperture) for reaching for both groups.

Interaction between serum BDNF and aerobic fitness predicts recognition memory in healthy young adults.

Convergent evidence from human and non-human animal studies suggests aerobic exercise and increased aerobic capacity may be beneficial for brain health and cognition. It is thought growth factors may mediate this putative relationship, particularly by augmenting plasticity mechanisms in the hippocampus, a brain region critical for learning and memory. Among these factors, glucocorticoids, brain derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), and vascular endothelial growth factor (VEGF), hormones that have considerable and diverse physiological importance, are thought to effect normal and exercise-induced hippocampal plasticity. Despite these predictions, relatively few published human studies have tested hypotheses that relate exercise and fitness to the hippocampus, and none have considered the potential links to all of these hormonal components. Here we present cross-sectional data from a study of recognition memory; serum BDNF, cortisol, IGF-1, and VEGF levels; and aerobic capacity in healthy young adults. We measured circulating levels of these hormones together with performance on a recognition memory task, and a standard graded treadmill test of aerobic fitness. Regression analyses demonstrated BDNF and aerobic fitness predict recognition memory in an interactive manner. In addition, IGF-1 was positively associated with aerobic fitness, but not with recognition memory. Our results may suggest an exercise adaptation-related change in the BDNF dose-response curve that relates to hippocampal memory.

Comparison of the Utrecht Scale for Evaluation of Rehabilitation-Participation with the ICF Measure of Participation and Activities Screener and the WHO Disability Assessment Schedule II in persons with spinal cord injury.

OBJECTIVE: To validate the Utrecht Scale for Evaluation of Rehabilitation-Participation (USER-Participation) in persons with spinal cord injury (SCI) using 2 International Classification of Functioning, Disability and Health (ICF)-based instruments: the ICF Measure of Participation and Activities-Screener (IMPACT-S) and the World Health Organization Disability Assessment Schedule II (WHODAS II). DESIGN: Validation study. Score distributions, internal consistency, and concurrent and discriminant validity were evaluated. SETTING: The community. PARTICIPANTS: Convenience sample of persons (N=157) with long-term SCI living in The Netherlands. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: USER-Participation, IMPACT-S, and WHODAS II. RESULTS: No instruments showed floor effects, and 3 out of 6 WHODAS II domains showed ceiling effects. Most scores showed adequate internal consistency (α≥.70), except for the USER-Participation frequency scale (.51) and 2 WHODAS II domains (.58-.60). Spearman correlation coefficients between the segregate USER-Participation scales were <.60 (range, .39-.46), showing that they cover separate aspects of participation. Concurrent validity of the USER-Participation was shown because >75% (83.3%) of the 24 hypotheses (Spearman correlation coefficients above or below .60) with the other measurement instruments were confirmed. Concurrent validity between the IMPACT-S and WHODAS II was not shown (53.8% of 13 hypotheses confirmed). All scores except 4 WHODAS II domains showed significant differences in participation between persons with paraplegia and tetraplegia. CONCLUSIONS: The USER-Participation showed generally satisfactory psychometric properties in Dutch persons with long-term SCI living in the community. The IMPACT-S showed the best psychometric properties, and the WHODAS II showed less favorable results. Future research on the USER-Participation should focus on validation in other languages and different diagnostic groups.

Conceptual limitations of balance measures for community-dwelling older adults.

BACKGROUND: Psychometric limitations of balance measures for community-dwelling elderly may be related to gaps in task and environmental representation. OBJECTIVE: The purposes of this study were: (1) to conduct item-level content analysis of balance measures for community-dwelling elderly people based on task and environmental factors and (2) to develop profiles of individual measures summarizing their task and environment representation. DESIGN: A systematic content analysis was conducted. METHODS: A literature search was conducted to identify balance measures. Item-level content analysis was based on 7 criteria related to task and environment: (1) task role, (2) environmental variation, (3) object interaction, (4) obstacle negotiation, (5) external forces, (6) dual-tasking, and (7) moving people or objects in the environment. RESULTS: Twenty-six measures, containing 167 items, were identified. Task role was fairly evenly distributed, with the majority of items examining gait tasks (32.3%), followed by dynamic body stability (29.9%) and static body stability (25.1%). The majority of items involved no environmental variation (58.1%), followed by variation of support surfaces (20.4%), visual conditions (13.2%), and both support and visual conditions (8.4%). Limited task role variability was seen within measures, with 73.1% of measures examining only one task role. Environmental variation was present in 65.3% of measures, primarily during static body stability tasks. Few measures involved object interaction (23.1%), obstacle negotiation (38.5%), external forces (11.5%), dual-tasking (7.7%), or moving people or objects (0%). LIMITATIONS: The classification framework was not externally validated. CONCLUSIONS: Existing measures focus on single-task assessment in static environments, underrepresenting postural control demands in daily-life situations involving dynamic changing environments, person-environment interactions, and multitasking. New items better reflecting postural control demands in daily-life situations are needed for more ecologically valid balance assessment. Individual balance measure profiles provided can help identify the most appropriate measure for a given purpose.

The impact of body-scaled information on reaching.

BACKGROUND: Environmental and task modifications are powerful methods used to affect action in rehabilitation and are frequently used by therapists. OBJECTIVE: The purpose of this study was to examine and quantify the relationship between hand size (person characteristics) and object size (environmental characteristics) and the effect of this relationship on the emergent reaching patterns for children and adults with typical development. DESIGN: This was a cross-sectional prospective study. METHODS: Seventeen children and 20 adults participated and were required to reach and grasp 10 pairs of cubes of different sizes. The dimensionless ratios were calculated by dividing the cube size by the aperture between index finger and thumb to quantify emergent reach and grasp patterns. A critical ratio was used to establish the shift from a 1-handed to an exclusive 2-handed reach pattern. RESULTS: The results demonstrated no significant difference in the mean critical ratios between the 2 groups. However, a 2-handed reach was used more frequently than a 1-handed reach at a significantly smaller ratio for children in comparison with adults. LIMITATIONS: The relational metrics between the cube and hand are only one contribution to the emergent reaching and grasping patterns. CONCLUSIONS: Children had more variability of reaching patterns than adults. A personal constraint, such as experience, and a task constraint of accuracy may account for the variability. The results encourage further research on body-scaled information for individuals with different personal constraints (eg, children with cerebral palsy) and the impact of body-scaled information on emergent actions.

Center of mass trajectory and orientation to ankle and knee in sagittal plane is maintained with forward lean when backpack load changes during treadmill walking.

Maintaining the normal shape and amplitude of the vertical trajectory of the center of mass (COM) during stance has been shown to maximize the efficiency of unloaded gait. Kinematic adaptations to load carriage, such as forward lean have yet to be understood in relation to COM movement. The purpose of this study is to better understand how load impacts the vertical COM(TSYS) trajectory and to clarify the impact of forward lean as it relates to the dynamics of sagittal plane COM(TSYS) movement during stance with changing load. 17 subjects walked on treadmill at a constant preferred walking velocity while nine different loads ranging from 12.5% to 40% bodyweight were systematically added and removed from a backpack. Kinematic data were collected using an Optotrak, three-dimensional motion analysis system and used to estimate position of the COM as well as segment and COM-to-joint vector orientation angles. The shape and amplitude of the COM vertical trajectory was maintained across all loaded conditions. The orientations of COM-to-ankle and -knee vectors were maintained in all loaded conditions except the heaviest load (40% BW). Results suggest that forward lean changed linearly with changes in load to maintain the COM-to-ankle and -knee vector orientations. COM vertical trajectory was maintained by a combination of invariants including lower-limb segment angles and a constant direction of toe-off impulse vector. The kinematic invariants found suggest a simplified control mechanism by which the system limits degrees of freedom and potentially minimizes torque about lower-extremity joints with added load.

Sensitivity to change and responsiveness of four balance measures for community-dwelling older adults.

BACKGROUND: Impaired balance has a significant negative impact on mobility, functional independence, and fall risk in older adults. Although several, well-respected balance measures are currently in use, there is limited evidence regarding the most appropriate measure to assess change in community-dwelling older adults. OBJECTIVE: The aim of this study was to compare floor and ceiling effects, sensitivity to change, and responsiveness across the following balance measures in community-dwelling elderly people with functional limitations: Berg Balance Scale (BBS), Performance-Oriented Mobility Assessment total scale (POMA-T), POMA balance subscale (POMA-B), and Dynamic Gait Index (DGI). DESIGN: Retrospective data from a 16-week exercise trial were used. Secondary analyses were conducted on the total sample and by subgroups of baseline functional limitation or baseline balance scores. METHODS: Participants were 111 community-dwelling older adults 65 years of age or older, with functional limitations. Sensitivity to change was assessed using effect size, standardized response mean, and paired t tests. Responsiveness was assessed using minimally important difference (MID) estimates. RESULTS: No floor effects were noted. Ceiling effects were observed on all measures, including in people with moderate to severe functional limitations. The POMA-T, POMA-B, and DGI showed significantly larger ceiling effects compared with the BBS. All measures had low sensitivity to change in total sample analyses. Subgroup analyses revealed significantly better sensitivity to change in people with lower compared with higher baseline balance scores. Although both the total sample and lower baseline balance subgroups showed statistically significant improvement from baseline to 16 weeks on all measures, only the lower balance subgroup showed change scores that consistently exceeded corresponding MID estimates. LIMITATIONS: This study was limited to comparing 4 measures of balance, and anchor-based methods for assessing MID could not be reported. CONCLUSIONS: Important limitations, including ceiling effects and relatively low sensitivity to change and responsiveness, were noted across all balance measures, highlighting their limited utility across the full spectrum of the community-dwelling elderly population. New, more challenging measures are needed for better discrimination of balance ability in community-dwelling elderly people at higher functional levels.

Monitoring walking and cycling of middle-aged to older community dwellers using wireless wearable accelerometers.

Changes in gait parameters have been shown to be an important indicator of several age-related cognitive and physical declines of older adults. In this paper we propose a method to monitor and analyze walking and cycling activities based on a triaxial accelerometer worn on one ankle. We use an algorithm that can (1) distinguish between static and dynamic functional activities, (2) detect walking and cycling events, (3) identify gait parameters, including step frequency, number of steps, number of walking periods, and total walking duration per day, and (4) evaluate cycling parameters, including cycling frequency, number of cycling periods, and total cycling duration. Our algorithm is evaluated against the triaxial accelerometer data obtained from a group of 297 middle-aged to older adults wearing an activity monitor on the right ankle for approximately one week while performing unconstrained daily activities in the home and community setting. The correlation coefficients between each of detected gait and cycling parameters on two weekdays are all statistically significant, ranging from 0.668 to 0.873. These results demonstrate good test-retest reliability of our method in monitoring walking and cycling activities and analyzing gait and cycling parameters. This algorithm is efficient and causal in time and thus implementable for real-time monitoring and feedback.

Profile of functional limitations and task performance among people with early- and middle-stage Parkinson disease.

BACKGROUND: Overall functional ability declines over time in people with Parkinson disease (PD). Established benchmarks are needed to allow clinicians and researchers to facilitate meaningful interpretation of data. OBJECTIVE: The purposes of this study were: (1) to report typical values for standard measures of functional ability commonly used in intervention studies and clinical practice with individuals in the early and middle stages of PD and (2) to describe the profile of functional limitations using the Hoehn and Yahr (H&Y) stages of disease and Unified Parkinson's Disease Rating Scale (UPDRS) motor scores. DESIGN: Cross-sectional data were obtained from 5 different studies. METHODS: Three hundred thirty-nine patients were evaluated for disease severity (UPDRS motor score); functional capacity (Continuous Scale Physical Functional Performance Test [CS-PFP]); balance and gait (Functional Reach Test [FRT], Timed "Up & Go" Test [TUG], 360-degree turn, Six-Minute Walk Test [6MWT], and Two-Minute Walk Test); and basic functional activities (supine-to-stand task, stand-to-supine task, and functional axial rotation [FAR]). RESULTS: The mean UPDRS motor score for the sample was 39.2 (SD=12.93). At each stage of PD (from least to most involved), scores on functional measures indicated a significant and progressively reduced functional status. Limitations began early in the disease for the CS-PFP and FAR. Losses in performance were consistent across all stages of disease for the CS-PFP, FRT, 6MWT, and FAR. Several measures demonstrated meaningful losses of function only in later stages of disease. Findings extend current appreciation of functional limitations that begin early in PD and can guide the choice of functional outcome measures at different stages of disease severity. LIMITATIONS: Data were obtained only from participants in H&Y stages 1 through 3 and only for some of the performance measures typically used. CONCLUSIONS: The findings demonstrate that functional loss occurs at different points in the disease process, depending on the task under consideration. The resulting profile of functional limitations provides benchmarks that clinicians and researchers can use to interpret and monitor status of patients.

Continuous monitoring of functional activities using wearable, wireless gyroscope and accelerometer technology.

The development of functional activity monitors (FAMs) will allow rehabilitation researchers and clinicians to evaluate treatment efficacy, to monitor compliance to exercise instructions, and to provide real time feedback in the treatment of movement disorders during the performance of daily activities. The purpose of the present study was to develop and test a small sized wearable FAM system comprised of three sensors positioned on the sternum and both thighs, wireless Bluetooth transmission capability to a smartphone, and computationally efficient activity detection algorithms for the accurate detection of functional activities. Each sensor was composed of a tri-axial accelerometer and a tri-axial gyroscope. Computationally efficient activity recognition algorithms were developed, using a sliding window of 1 second, the variability of the tilt angle time series and power spectral analysis. In addition, it includes a decision tree that identifies postures such as sitting, standing and lying, walking at comfortable, slow and fast speeds, transitions between these functional activities (e.g, sit-to-stand and stand-to-sit), activity duration and step frequency. In a research lab setting the output of the FAM system, video recordings and a 3D motion analysis system were compared in 10 healthy young adults. The results show that the agreement between the FAM system and the video recordings ranged from 98.10% to 100% for all postures, transfers and walking periods. There were no significant differences in activity durations and step frequency between measurement instruments.

A Dynamic Systems: constraints approach to rehabilitation / Uma abordagem dos sistemas dinâmicos: restrições para a reabilitação

BACKGROUND: Classification systems (Nagi, International Classification for Function [ICF]) have become popular for categorizing the level of ability (ICF) or disability (Nagi) associated with movement disorders. Nevertheless, these classifications do not explore the ways in which one level may influence other levels. For example, how might the weakness and stiffness associated with some cases of cerebral palsy result in a stereotypical toe-gait? In this overview we describe a dynamic systems/constraints (DS/C) approach to understand relationships between levels, and how the approach can be used to rationalize a novel process for the evaluation and treatment of movement disorders. OBJECTIVES: There are three specific aims in this paper: first to present a general systems approach to understanding behavior at different levels; second to present tools of, and the results of empirical work using the DS/C approach; third to discuss the clinical implications and results of clinical interventions motivated by DS/C analysis for children with cerebral palsy, and individuals with Parkinson disease.

CONTEXTUALIZAÇÃO: Sistemas de classificação (Nagi e Classificação International de Funcionalidade (CIF)) têm se tornado populares para categorização do nível de habilidade (CIF) ou de incapacidade (Nagi) associado com distúrbios do movimento. No entanto, essas classificações não exploram as formas pelas quais um nível pode influenciar outros níveis; por exemplo, como a fraqueza e a rigidez observadas em alguns casos de paralisia cerebral podem resultar no padrão estereotipado de marcha equina. Neste artigo, descreve-se uma abordagem denominada sistemas dinâmicos/restrições (DS/C) para compreender as relações entre níveis e como ela pode ser utilizada para racionalizar um novo processo que norteie a avaliação e a intervenção de distúrbios do movimento. OBJETIVOS: Este artigo tem três objetivos específicos: apresentar uma abordagem geral sistêmica para compreender o comportamento em diferentes níveis de análise; apresentar ferramentas e resultados de estudos empíricos que utilizaram a abordagem DS/C e, por fim, discutir as implicações clínicas e os resultados de intervenções motivadas pela análise DS/C voltadas para crianças com paralisia cerebral e indivíduos com Doença de Parkinson.

Visuospatial perception and navigation in Parkinson's disease.

A shifted field of view, an altered perception of optic flow speed, and gait asymmetries may influence heading direction in Parkinson's disease (PD). PD participants (left body-side onset, LPD, n=14; right body-side onset, RPD, n=9) and Healthy Control participants (n=17) walked a virtual hallway in which the optic flow speeds of the walls varied. Three-dimensional kinematics showed participants veered away from the faster moving wall. Although veering normally occurs toward the side with smaller step length, in both LPD and RPD this bias was overridden by a shifted field of view, which caused veering in the opposite direction, toward the side of the brain with more basal ganglia damage.

Self-management rehabilitation and health-related quality of life in Parkinson's disease: a randomized controlled trial.

The purpose of this randomized controlled trial was to determine whether increasing hours of self-management rehabilitation had increasing benefits for health-related quality of life (HRQOL) in Parkinson's disease beyond best medical treatment, whether effects persisted at 2 and 6 months of follow-up, and whether targeted compared with nontargeted HRQOL domains responded more to rehabilitation. Participants on best medication therapy were randomly assigned to one of three conditions for 6 weeks intervention: 0 hours of rehabilitation; 18 hours of clinic group rehabilitation plus 9 hours of attention control social sessions; and 27 hours of rehabilitation, with 18 in clinic group rehabilitation and 9 hours of rehabilitation designed to transfer clinic training into home and community routines. Results (N = 116) showed that at 6 weeks, there was a beneficial effect of increased rehabilitation hours on HRQOL measured with the Parkinson's Disease Questionnaire-39 summary index (F(1,112) = 6.48, eta = 0.23, CI = 0.05-0.40, P = 0.01). Benefits persisted at follow-up. The difference between 18 and 27 hours was not significant. Clinically relevant improvement occurred at a greater rate for 18 and 27 hours (54% improved) than for 0 hours (18% improved), a significant 36% difference in rates (95% CI = 20-52% difference). Effects were largest in two targeted domains: communication and mobility. More concerns with mobility and activities of daily living at baseline predicted more benefit from rehabilitation.

A dynamic systems/constraints approach to rehabilitation.

BACKGROUND: Classification systems (Nagi, International Classification for Function [ICF]) have become popular for categorizing the level of ability (ICF) or disability (Nagi) associated with movement disorders. Nevertheless, these classifications do not explore the ways in which one level may influence other levels. For example, how might the weakness and stiffness associated with some cases of cerebral palsy result in a stereotypical toe-gait? In this overview we describe a dynamic systems/constraints (DS/C) approach to understand relationships between levels, and how the approach can be used to rationalize a novel process for the evaluation and treatment of movement disorders. OBJECTIVES: There are three specific aims in this paper: first to present a general systems approach to understanding behavior at different levels; second to present tools of, and the results of empirical work using the DS/C approach; third to discuss the clinical implications and results of clinical interventions motivated by DS/C analysis for children with cerebral palsy, and individuals with Parkinson disease.

Effects of optic flow speed and lateral flow asymmetry on locomotion in younger and older adults: a virtual reality study.

The purpose of the study is to investigate whether there are age-related differences in locomotion due to changes in presence of vision, optic flow speed, and lateral flow asymmetry using virtual reality technology. Gait kinematics and heading direction were measured using a three-dimensional motion analysis system. Although older and younger adults were affected differentially by the availability of vision, a greater dependence on optic flow information in older adults during walking was not found. Linear relations were observed between walking performance and flow speed as well as heading direction and flow asymmetry. The findings suggest that the ability to integrate optic flow information into the multimodal system for assessment of walking speed and heading direction is comparable in older and younger adults.