Regina T. Harbourne

Optimal movement variability: a new theoretical perspective for neurologic physical therapy.

Variability is a natural and important feature of human movement. Using existing theoretical frameworks as a foundation, we propose a new model to explain movement variability as it relates to motor learning and health. We contend that mature motor skills and healthy states are associated with an optimal amount of movement variability. This variability also has form and is characterized by a chaotic structure. Less than optimal movement variability characterizes biological systems that are overly rigid and unchanging, whereas greater than optimal variability characterizes systems that are noisy and unstable. Both situations characterize systems that are less adaptable to perturbations, such as those associated with abnormal motor development or unhealthy states. From our perspective, the goal of neurologic physical therapy should be to foster the development of this optimal amount of movement variability by incorporating a rich repertoire of movement strategies. The development of such a repertoire can be enhanced by incorporating a multitude of experiences within the therapeutic milieu. Promoting complex variation in human movement allows either motor development or the recovery of function after injury not to be hard coded, but determined instead by the active engagement of the individual within their environment. Measurement tools derived from nonlinear dynamics that characterize the complexity of movement variability provide useful means of testing these propositions. To illustrate, we present 2 clinical case studies, one pediatric and one adult, where we applied our theoretical framework to measuring change in postural control.

Movement Variability and the Use of Nonlinear Tools: Principles to Guide Physical Therapist Practice

Fields studying movement generation, including robotics, psychology, cognitive science, and neuroscience, utilize concepts and tools related to the pervasiveness of variability in biological systems. The concepts of variability and complexity and the nonlinear tools used to measure these concepts open new vistas for physical therapist practice and research in movement dysfunction of all types. Because mounting evidence supports the necessity of variability for health and functional movement, this perspective article argues for changes in the way therapists view variability, both in theory and in action. By providing clinical examples, as well as applying existing knowledge about complex systems, the aim of this article is to create a springboard for new directions in physical therapist research and practice.

Grounding Early Intervention: Physical Therapy Cannot Just Be About Motor Skills Anymore

This perspective article provides support for 4 interrelated tenets: grounded perceptual-motor experience within cultural and social contexts forms cognition; exploration through early behaviors, such as object interaction, sitting, and locomotion, broadly facilitates development; infants and children with limited exploration are at risk for global developmental impairments; and early interventions targeting exploratory behaviors may be feasible and effective at advancing a range of abilities across developmental domains and time. These tenets emphasize that through the promotion of early perceptual-motor behaviors, broader, more global developmental advancements can be facilitated and future delays can be minimized across domains for infants and children with special needs. Researchers, educators, and clinicians should build on these tenets to further demonstrate the effectiveness of targeted early interventions. The goals of these interventions should be not only to advance targeted perceptual-motor skills in the moment but also to more broadly advance future abilities and meet the early intervention goal of maximizing childrens learning potential.

Variability in Postural Control During Infancy: Implications for Development, Assessment, and Intervention

Variability is commonly considered a key to typical motor development. However, multiple definitions and quantification systems have limited the clinical interpretation of variability and the translation of developmental research to assessment and intervention. The purposes of this perspective article are to highlight the importance of statistical variability and complexity in postural control during development and to describe implications for assessment and intervention during infancy and early childhood. Five tenets are proposed describing the role of variability in postural control to support movement experiences, exploration, and global development. Evidence for assessment and intervention focused on variability in postural control are introduced.

Early, Accurate Diagnosis and Early Intervention in Cerebral Palsy: Advances in Diagnosis and Treatment

Importance Cerebral palsy describes the most common physical disability in childhood and occurs in 1 in 500 live births. Historically, the diagnosis has been made between age 12 and 24 months but now can be made before 6 months’ corrected age. Objectives To systematically review best available evidence for early, accurate diagnosis of cerebral palsy and to summarize best available evidence about cerebral palsy–specific early intervention that should follow early diagnosis to optimize neuroplasticity and function. Evidence Review This study systematically searched the literature about early diagnosis of cerebral palsy in MEDLINE (1956-2016), EMBASE (1980-2016), CINAHL (1983-2016), and the Cochrane Library (1988-2016) and by hand searching. Search terms included cerebral palsy, diagnosis, detection, prediction, identification, predictive validity, accuracy, sensitivity, and specificity. The study included systematic reviews with or without meta-analyses, criteria of diagnostic accuracy, and evidence-based clinical guidelines. Findings are reported according to the PRISMA statement, and recommendations are reported according to the Appraisal of Guidelines, Research and Evaluation (AGREE) II instrument. Findings Six systematic reviews and 2 evidence-based clinical guidelines met inclusion criteria. All included articles had high methodological Quality Assessment of Diagnostic Accuracy Studies (QUADAS) ratings. In infants, clinical signs and symptoms of cerebral palsy emerge and evolve before age 2 years; therefore, a combination of standardized tools should be used to predict risk in conjunction with clinical history. Before 5 months’ corrected age, the most predictive tools for detecting risk are term-age magnetic resonance imaging (86%-89% sensitivity), the Prechtl Qualitative Assessment of General Movements (98% sensitivity), and the Hammersmith Infant Neurological Examination (90% sensitivity). After 5 months’ corrected age, the most predictive tools for detecting risk are magnetic resonance imaging (86%-89% sensitivity) (where safe and feasible), the Hammersmith Infant Neurological Examination (90% sensitivity), and the Developmental Assessment of Young Children (83% C index). Topography and severity of cerebral palsy are more difficult to ascertain in infancy, and magnetic resonance imaging and the Hammersmith Infant Neurological Examination may be helpful in assisting clinical decisions. In high-income countries, 2 in 3 individuals with cerebral palsy will walk, 3 in 4 will talk, and 1 in 2 will have normal intelligence. Conclusions and Relevance Early diagnosis begins with a medical history and involves using neuroimaging, standardized neurological, and standardized motor assessments that indicate congruent abnormal findings indicative of cerebral palsy. Clinicians should understand the importance of prompt referral to diagnostic-specific early intervention to optimize infant motor and cognitive plasticity, prevent secondary complications, and enhance caregiver well-being.

Nonlinear analysis of sitting postural sway indicates developmental delay in infants

BACKGROUND Upright sitting is one of the first developmental motor milestones achieved by infants, and sitting postural sway provides a window into the developing motor control system. A variety of posture sway measures can be used, but the optimal measures for infant development have not been identified. METHODS We have collected sitting postural sway data from two groups of infants, one with typical development (n=33), and one with delayed development and either diagnosed with or at risk for cerebral palsy (n=26), when the infants had developed to the point where they could just maintain sitting for about 10s. Postural sway data was collected while infants were sitting on a force platform, and the center of pressure was analyzed using both linear and nonlinear measures. FINDINGS Our results showed that a nonlinear measure, the largest Lyapunov exponent, was the only parameter of postural sway that revealed significant differences between infants with typical versus delayed development. The largest Lyapunov exponent was found to be higher for typically developing infants, indicating less repeated patterning in their movement coordination. INTERPRETATIONS A nonlinear measure such as largest Lyapunov exponent may be useful as an identifier of pathology and as a yardstick for the success of therapeutic interventions.

Effectiveness of motor interventions in infants with cerebral palsy: a systematic review

To systematically review the evidence on the effectiveness of motor interventions for infants from birth to 2 years with a diagnosis of cerebral palsy or at high risk of it.

A Comparison of Interventions for Children With Cerebral Palsy to Improve Sitting Postural Control: A Clinical Trial

Background The ability to sit independently is fundamental for function but delayed in infants with cerebral palsy (CP). Studies of interventions directed specifically toward sitting in infants with CP have not been reported. Objective The purpose of this study was to compare 2 interventions for improving sitting postural control in infants with CP. Design For this randomized longitudinal study, infants under 2 years of age and at risk for CP were recruited for intervention directed toward sitting independence. Setting The intervention was conducted at home or at an outpatient facility. Patients and Intervention Fifteen infants with typical development (mean age at entry=5 months, SD=0.5) were followed longitudinally as a comparison for postural variables. Thirty-five infants with delays in achieving sitting were recruited. Infants with delays were randomly assigned to receive a home program (1 time per week for 8 weeks; mean age=15.5 months, SD=7) or a perceptual-motor intervention (2 times per week for 8 weeks; mean age=14.3 months, SD=3). Measurements The primary outcome measure was center-of-pressure (COP) data, from which linear and nonlinear variables were extracted. The Gross Motor Function Measure (GMFM) sitting subsection was the clinical outcome measure. Results There was a main effect of time for the GMFM sitting subscale and for 2 of the COP variables. Interaction of group × time factors indicated significant differences between intervention groups on 2 COP measures, in favor of the group with perceptual-motor intervention. Limitations The small number of infants limits the ability to generalize the findings. Conclusions Although both groups made progress on the GMFM, the COP measures indicated an advantage for the group with perceptual-motor intervention. The COP measures appear sensitive for assessment of infant posture control and quantifying intervention response.

Reliability of Center of Pressure Measures for Assessing the Development of Sitting Postural Control in Infants With or at Risk of Cerebral Palsy

OBJECTIVE To establish the test-retest reliability of linear and nonlinear measures, including intra- and intersession reliability, when used to analyze the center of pressure (COP) time series during the development of infant sitting postural control in infants with or at risk for cerebral palsy (CP). DESIGN Longitudinal study. SETTING University hospital laboratory. PARTICIPANTS Infants with or at risk for CP (N=18; mean age ± SD at entry into the study, 13.7±3.6mo). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Infant sitting COP data were recorded for 3 trials at each session (2 sessions for each month within 1 week) for 4 consecutive months. The linear COP parameters of the root mean square, the range of sway for both the anterior-posterior and the medial-lateral directions, and the sway path were calculated. In addition, the nonlinear parameters of approximate entropy, Lyapunov exponent (LyE), and the correlation dimension for both directions were also calculated. Intra- and intersession reliability was computed by the intraclass correlation coefficient (ICC). RESULTS Regarding nonlinear measures, LyE showed high intra- and intersession ICC values in comparison with all other parameters evaluated. Intrasession and intersession reliability increased overall in the last 2 months of data collection and as sitting posture improved. CONCLUSIONS Our results suggested that the methodology presented is a reliable way of examining the development of sitting postural control in infants with or at risk for CP, and the reliability results generally parallel values found in sitting postural behavior in typical infants. Therefore, this methodology may be helpful in examining efficacy of therapy protocols directed at advancing sitting postural control in infants with motor developmental delays.

Use of information entropy measures of sitting postural sway to quantify developmental delay in infants.

BackgroundBy quantifying the information entropy of postural sway data, the complexity of the postural movement of different populations can be assessed, giving insight into pathologic motor control functioning.MethodsIn this study, developmental delay of motor control function in infants was assessed by analysis of sitting postural sway data acquired from force plate center of pressure measurements. Two types of entropy measures were used: symbolic entropy, including a new asymmetric symbolic entropy measure, and approximate entropy, a more widely used entropy measure. For each method of analysis, parameters were adjusted to optimize the separation of the results from the infants with delayed development from infants with typical development.ResultsThe method that gave the widest separation between the populations was the asymmetric symbolic entropy method, which we developed by modification of the symbolic entropy algorithm. The approximate entropy algorithm also performed well, using parameters optimized for the infant sitting data. The infants with delayed development were found to have less complex patterns of postural sway in the medial-lateral direction, and were found to have different left-right symmetry in their postural sway, as compared to typically developing infants.ConclusionThe results of this study indicate that optimization of the entropy algorithm for infant sitting postural sway data can greatly improve the ability to separate the infants with developmental delay from typically developing infants.