Approximate entropy used to assess sitting postural sway of infants with developmental delay

Infant sitting postural sway provides a window into motor development at an early age. The approximate entropy, a measure of randomness, in the postural sway was used to assess developmental delay, as occurs in cerebral palsy. Parameters used for the calculation of approximate entropy were investigated, and approximate entropy of postural sway in early sitting was found to be lower for infants with developmental delay in the anterior–posterior axis, but not in the medial–lateral axis. Spectral analysis showed higher frequency features in the postural sway of early sitting of infants with typical development, suggesting a faster control mechanism is active in infants with typical development as compared to infants with delayed development, perhaps activated by near-fall events

Sensory Information Utilization and Time Delays Characterize Motor Developmental Pathology in Infant Sitting Postural Control

Sitting is one of the first developmental milestones that an infant achieves. Thus measurements of sitting posture present an opportunity to assess sensorimotor development at a young age. Sitting postural sway data were collected using a force plate, and the data were used to train a neural network controller of a model of sitting posture. The trained networks were then probed for sensitivity to position, velocity, and acceleration information at various time delays. Infants with typical development developed a higher reliance on velocity information in control in the anterior-posterior axis, and used more types of information in control in the medial-lateral axis. Infants with delayed development, where the developmental delay was due to cerebral palsy for most of the infants in the study, did not develop this reliance on velocity information, and had less reliance on short latency control mechanisms compared with infants with typical development

Motor control of the lower extremity musculature in children with cerebral palsy

The aim of this investigation was to quantify the differences in torque steadiness and variability of the muscular control in children with cerebral palsy (CP) and typically developing (TD) children. Fifteen children with CP (age = 14.2 ± 0.7 years) that had a Gross Motor Function Classification System (GMFCS) score of I-III and 15 age and gender matched TD children (age = 14.1 ± 0.7 years) participated in this investigation. The participants performed submaximal steady-state isometric contractions with the ankle, knee, and hip while surface electromyography (sEMG) was recorded. An isokinetic dynamometer was used to measure the steady-state isometric torques while the participants matched a target torque of 20% of the subject’s maximum voluntary torque value. The coefficient of variation was used to assess the amount of variability in the steady-state torque, while approximate entropy was used to assess the regularity of the steady-state torque over time. Lastly, the distribution of the power spectrum of the respective sEMG was evaluated. The results of this investigation were: 1) children with CP had a greater amount of variability in their torque steadiness at the ankle than TD children, 2) children with CP had a greater amount of variability at the ankle joint than at the knee and hip joint, 3) the children with CP had a more regular steady-state torque pattern than TD children for all the joints, 4) the ankle sEMG of children with CP was composed of higher harmonics than that of the TD children

Reliability of Center of Pressure Measures for Assessing the Development of Sitting Postural Control

Objectives: To determine the reliability of linear and nonlinear tools, including intrasession and intersession reliability, when used to analyze the center of pressure (COP) time series during the development of infant sitting postural control. Design: Longitudinal study. Setting: University hospital laboratory. Participants: Typically developing infants (N33; mean SD age at entry in the study, 152.417.6d). Interventions: Not applicable. Main Outcome Measures: Infants were tested twice in 1 week at each of the 4 months of the study. Sitting COP data were recorded for 3 trials at each session (2 each month within 1 week). The linear COP parameters of root mean square and range of sway for both the anterior-posterior and the mediallateral directions, and the sway path, were calculated. The nonlinear parameters of approximate entropy, Lyapunov exponent, and correlation dimension for both directions were also calculated. Intrasession and intersession reliability was quantified by the intraclass correlation coefficient (ICC). Results: The nonlinear tool of approximate entropy presented high intrasession and intersession ICC values compared with all other parameters evaluated. Generally, intrasession and intersession reliability increased in the last 2 months of the data collection and as sitting posture matured. Conclusions: Our results showed that the evaluation of COP data is a reliable method of investigating the development of sitting postural control. The present study emphasizes the need for establishing COP reliability before using it as a method of examining intervention progress directed at improving the sitting postural abilities in infants with motor developmental delays

Methods to Improve the Reliability of the Functional Reach Test in Children and Adolescents With Typical Development

Purpose: Test-retest reliability of the Functional Reach Test was examined in children with typical development by comparing standard and alternate methods. Methods: Eighty subjects ages seven to 16 years were tested and 69 retested for four methods of Functional Reach Test (ie, one-arm finger-to-finger, two-arm finger-to-finger, one-arm toe-to-finger, and two-arm toe-to-finger). Intraclass correlation coefficients and limits of agreement were calculated. Results: Intraclass correlation coefficients were high in toe-to-finger measurement methods (0.97– 0.98) for the entire group and specific age groups (00.83–0.93). Toe-to-finger methods were more reliable than finger-to-finger methods. The two-arm toe-to-finger method had the best limis of agreement with approximately ±5 cm indicated by the 95% confidence interval. Conclusions: Test-retest reliability using a toe-to-finger method of measuring is stronger than previously reported when using traditional methods. Limits of agreement analyses imply a change of 5 cm or more is likely to represent a true clinical difference when using the two-arm toe-to-finger method

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 10 s. 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

Factors Affecting Functional Reach Scores in Youth with Typical Development

Purpose: Functional Reach Test scores were examined for the effects of traditional and alternate methods and subject characteristics. Methods: Eighty subjects aged 7 to 16 years were tested. Effects of measurement method (from finger-to-finger or from toe-to-finger) and style of reach (1 or 2 arms) were investigated. Five subject variables were analyzed for interactions among the methods and groups defined by subject characteristics. Results: Measurement method and style of reach showed a significant interaction. Interaction of method with subject characteristics was significant for age, height, and base of support only. Height groups by quartile were significantly different and scores increased with height, especially in toes-to-finger methods. Conclusions: Functional Reach Test scores were affected by method of reach and method of measurement. Height categories may be more useful when using the test for discriminative purposes, especially with toes-to-finger methods

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

Background: By 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. Methods: In 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. Results: The 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. Conclusion: The 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

Development of Upper Body Coordination During Sitting in Typically Developing Infants

Our goal was to determine how the actions of the thorax and the pelvis are organized and coordinated to achieve independent sitting posture in typically developing infants. The participants were 10 typically developing infants who were evaluated longitudinally from first onset of sitting until sitting independence. Each infant underwent nine testing sessions. The first session included motor evaluation with the Peabody test. The other eight sessions occurred over a period of 4 mo where sitting behavior was evaluated by angular kinematics of the thorax and the pelvis. A physical therapist evaluated sitting behavior in each session and categorized it according to five stages. The phasing relationship of the thorax and the pelvis was calculated and evaluated longitudinally using a one-way analysis of variance. With development, the infants progressed from an in-phase (moving in the same direction) to an out-of-phase (moving in an opposite direction) coordinative relationship between the thorax and the pelvis segments. This change was significant for both sagittal and frontal planes of motion. Clinically, this relationship is important because it provides a method to quantify infant sitting postural development, and can be used to assess efficacy of early interventions for pediatric populations with developmental motor delays