Nonlinear analysis of the development of sitting postural control

The development of sitting postural control in five normal infants was examined longitudinally at three stages of sitting: Stage 1, when infants could hold up their head and upper trunk, but could not sit independently; Stage 2, when infants began to sit independently briefly; and Stage 3, when infants could sit independently. Methods from nonlinear dynamics were used to analyze center of pressure (COP) data during sitting in terms of stability of the neuromuscular system (Lyapunov Exponent), movement dimensionality (Correlation Dimension), and complexity/regularity (Approximate Entropy). Results indicated significant changes in the nonlinear measures over time, with increased stability and increased regularity revealing a more stable and periodic strategy of maintaining postural control. Dimensionality decreased from Stage 1 to 2, indicating a constraint of the degrees of freedom. Subsequently, dimensionality increased from Stage 2 to 3, indicating a release of the degrees of freedom as sitting independence emerged. Nonlinear analysis of the COP time series supports the perspective that the development of postural control is a dynamic process whereby the infant learns to control the body\u27s degrees of freedom to achieve the sitting posture

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 therapy practice and research in movement dysfunction of all types. Because mounting evidence supports the necessity of variability for health and functional movement, we argue in this perspective 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, we hope to create a springboard for new directions in physical therapy research and practice

Severity and Characteristics of Developmental Delay Can Be Assessed Using Variability Measures of Sitting Posture

Purpose: We sought to identify measures of variability from sitting postural sway that are significantly different among infants who were developing typically, those who were developmentally delayed or hypotonic, and those who later on had a diagnosis of spastic or athetoid cerebral palsy. Methods: Sixty-five infants were evaluated when they were just developing the ability to sit upright by assessing center of pressure (COP) data, using measures of both amount and temporal organization of COP variability. Results: The results indicated that measures of variability of COP could discriminate between infants with developmental delay and infants with cerebral palsy and add to the description of sitting postural behavior. Conclusions: Our method of evaluating sitting postural control could be an objective tool to help describe distinctive features of motor delay in an individual infant and could lead in the design of selective therapeutic interventions for improving postural control of infants with motor delays

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

Sitting and Looking: The Development of Stability and Visual Exploration

This longitudinal study focused on the interaction of developing sitting postural control with look time, which served as a measure for cognitive processing. Twenty-eight typically developing infants and 16 infants with motor delays were evaluated using center-of-pressure measures to assess stability of sitting postural control and videography to assess look time at objects, at three progressive stages of sitting development. Results indicated that look time decreased significantly in conjunction with a significant increase in postural stability in both groups as sitting progressed to independence. Infants with motor delays showed significantly longer looks when compared to typical infants at the middle stage of sitting. We conclude that developmental changes in look time are related to changes in sitting postural control, and infants with motor delay may have greater difficulty looking during emerging postural control skills in sitting. Early interventionists may use look time as an indicator of sitting effort and cognitive processing during assessment and program planning

International Strategies for Addressing the Needs of Children with Disabilities: Comparing pediatric therapy services in Italy and the United States

This paper introduces and compares the professions of Neuro and Psychomotor Therapist of Developmental Age and pediatric physical therapy. Although pediatric physical therapy practice is prevalent in the United States, Italy utilizes another profession which encompasses many features of physical therapy, but also incorporates neuropsychological factors, specifically for children

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

Anterior-posterior and medial-lateral control of sway in infants during sitting acquisition does not become adult-like

We examined (1) how sitting postural control in infants develops in the anterior–posterior (A/P) and medial–lateral (M/L) directions of sway, and (2) whether this control is already adult-like during the late phase of infant\u27s sitting acquisition. COP data were acquired from 14 healthy infants (from the onset of sitting until independent sitting) and 21 healthy adults while sitting on a force platform. Attractor dimensionality (CoD: correlation dimension), attractor predictability (LyE: largest Lyapunov exponent), and sway variability (RMS: root-mean square) were calculated from the COP data to evaluate postural control. In the A/P direction, sitting was mastered by the infants by decreasing the active degrees of freedom of the postural system (decreased CoD), using a more predictable and (locally) stable sway (decreased LyE), and increasing sway variability (increased RMS). Control of sitting became practically simple, stable and exploratory with infant development. This may support the hypothesis that the sitting posture serves as the foundation for the development of other motor skills, as reaching. In the M/L direction, only sway variability decreased with development, possibly due to changes in the infant\u27s body dimensions. Taken together, these findings indicate that early in development the focus is more in the A/P than the M/L direction. Adults’ postural control was found more adaptable than the infants in both directions, involving more active degrees of freedom and less predictable sway patterns. Identifying the factors that make the dynamics of the postural system adult-like requires further research

Sitting Postural Control in Infants With Typical Development, Motor Delay, or Cerebral Palsy

Purpose: To determine whether infants born full-term, infants born preterm with motor delays, and infants born preterm who have a diagnosis of cerebral palsy (CP) differed in postural control at the emergence of early sitting. Methods: Thirty infants born at term who were developing typically, 6 infants born preterm who were later diagnosed with CP, and 5 infants born preterm who were delayed in motor development participated in this study. Center-of-pressure data from unsupported sitting were recorded and analyzed using measures of both amount and temporal organization of center-of-pressure variability. Results: Infants born full-term, infants born preterm with motor delays, and infants born preterm who have a diagnosis of CP exhibited dissimilar movement-control strategies at the onset of sitting. Conclusions: The present findings may be helpful in directing and testing intervention protocols for infants born preterm

Center of pressure and the projection of the time-course of sitting skill acquisition

A normal time-course for the acquisition of sitting is essential. A delay in sitting may affect other developmental milestones, resulting in deficiencies in overall skill. Therefore, our aim was to identify variables whose measures at the very beginning of sitting would allow for the projection of the evolution of the sitting skill. Center of pressure data were collected from the postural sway of twenty-six typically developing infants while sitting on a force platform with a beginning ability to sit upright. Spatial, temporal and frequency variables of postural sway were obtained from both the medial/lateral and anterior/posterior directions of sway. Discriminant function analysis was conducted to identify potential predictors of the duration between onset and fully independent sitting. Gender (p=0.025), Median Frequency (p=0.006), and Correlation Dimension (p=0.002) were identified to be predictive of grouping with 73.1% correct classification of the participating infants into short, mid, and long delay groups. In conclusion, measures taken at the earliest stage of sitting may allow the projection of the time-course to achieve independent sitting for typical infants. This approach may be useful for monitoring typical development