Reliability of center of pressure measures for assessing the development of sitting postural control

Reaching While Learning to Sit: Capturing the Kinematics of Co-Developing Skills at Home

This study examined the co-development of infant reaching and postural control across the transition to arms-free sitting at home. We observed infants with typical likelihood (TL; n = 24) and elevated likelihood (EL; n = 20) for autism at four biweekly sessions spanning the transition to arms-free sitting (infant age = 4.5-8 months at first session). At each session, infants sat on a pressure-sensitive mat with external support or independently, wore magneto-inertial sensors on both wrists, and reached for toys presented at midline. Analyses focused on characterizing and comparing control of sitting during reaching actions and standard kinematic metrics of reaching during Supported versus Independent Sitting. Although EL infants achieved arms-free sitting later than TL peers, there were no group differences on any measures. Across sessions, infants' control of the sitting posture during concurrent reaching movements improved in both contexts, though they were less stable as they reached when sitting independently compared to when sitting with support. A similar effect was apparent in the kinematics of reaches, with overall improvement over time, but evidence of poorer control in Independent relative to Supported Sitting. Taken together, these findings underscore the mutually influential and dynamic relations between emerging skills and well-established behaviors.

Standing Posture in Motor and Cognitive Dual-Tasks during Smartphone Use: Linear and Nonlinear Analysis of Postural Control

Analysis of the center of pressure (CoP) during cognitive or motor dual-tasking is widely used to characterize postural control. Most studies use traditional measures of CoP to quantify postural control, but given its complexity, nonlinear analysis of CoP is of growing interest in the area. This study aims to analyze CoP behavior in healthy young adults during standing posture performance while simultaneously performing motor or cognitive tasks on a smartphone, using linear and nonlinear analysis of CoP. Thirty-six healthy participants (23.08 ± 3.92 years) were found eligible for this study. They performed a single task (ST), cognitive dual-task (cog-DT), and motor dual-task (mot-DT). The total excursion of CoP, displacement of CoP in the anterior-posterior and medial-lateral directions, mean total velocity of CoP, and mean anterior-posterior and medial-lateral velocities of CoP were measured with a force plate. Approximate entropy (ApEn) of the anterior-posterior (ApEn-AP) and medial-lateral (ApEn-ML) displacement of CoP were also calculated. The results showed that dual-task costs for the total excursion, displacement in the anterior-posterior direction, mean total velocity, and mean anterior-posterior velocity of CoP were greater during the cog-DT than the mot-DT (p < 0.05). In the nonlinear analysis of the CoP, there was no difference (p > 0.05) between the cog-DT and mot-DT for ApEn values of the anterior-posterior and medial-lateral time series of the CoP. Both linear and nonlinear analyses showed differences between the cog-DT and ST (p < 0.05), revealing a decline in postural control during the cog-DT compared with the ST. In conclusion, performing a cog-DT causes sway impairments and lower postural control efficacy compared with motor single and dual-tasks. Furthermore, both linear and nonlinear analyses were able to distinguish between conditions.

Quantification of the development of trunk control in healthy infants using inertial measurement units

Trunk motor control is essential for the proper functioning of the upper extremities and is an important predictor of gait capacity in children with delayed development. Early diagnosis and intervention could increase the trunk motor capabilities in later life, but current tools used to assess the level of trunk motor control are largely subjective and many lack the sensitivity to accurately monitor development and the effects of therapy. Inertial measurement units could yield an objective quantitative assessment that is inexpensive and easy-to-implement. We hypothesized that root mean square of jerk, a proxy for movement smoothness, could be used to distinguish age and thereby presumed motor development. We attached a sensor to the trunks of six young children with no known developmental deficits. Root mean square of jerk decreases with age, up to 24 months, and is correlated to a more established method, i.e., center-of-pressure velocity, as well as other standard inertial measurement unit outputs. This metric therefore shows potential as a method to differentiate trunk motor control levels.

Evaluation of sitting and standing postural balance in cerebral palsy by center-of-pressure measurement using force plates: comparison with clinical measurements

BACKGROUND

Center-of-pressure (CoP) measurements have been studied for assessing balance control. While CoP measurements using force plates have been used to assess standing balance in children with cerebral palsy (CP), it has not been assessed in a sitting position, which specifically reflects trunk postural control.

RESEARCH QUESTION

The purpose of this study was to compare CoP measurements using force plates during both standing and sitting trials with the Pediatric Balance Scale (PBS) in children with spastic CP.

METHODS

We recruited 26 children with spastic CP (7.8 ± 3.4 years, 4-13 years) and used the PBS, a validated evaluation tool that measures static and dynamic balance control. We took CoP measurements using force plates during sitting and standing. For both trials, subjects stayed still for 10 s with their eyes open or closed. We calculated the CoP velocity, mediolateral (ML) and anteroposterior (AP) velocity, and ML and AP displacements of CoP.

RESULTS AND SIGNIFICANCE

During standing trials, static PBS standing scores negatively correlated with more AP displacement and velocity than ML displacement and velocity (p < 0.05). During sitting trials, dynamic PBS sitting scores negatively correlated with ML displacement and velocity (p < 0.05). CoP parameters in the ML direction of the sitting position and CoP parameters in the AP direction of the standing position may better reflect the balance control in children with spastic CP.

W, DeVeney S. Postural control may drive the development of other domains in infancy

BACKGROUND

To examine differences in sitting posture in infants at low- and high-risk for autism spectrum disorder and to establish the relationship between sitting postural control and other developmental domains.

METHODS

A total of 19 infants participated in the study. Eight infants at high-risk and 11 infants at low-risk for autism spectrum disorder. Sitting posture at 6 months was evaluated using a force platform while center of pressure data were acquired. We utilized traditional tools of center of pressure analysis, such as range, median frequency and frequency dispersion, as well as non-linear tools such as Sample Entropy for both the medial-lateral and anterior-posterior directions. At 12 months we used the Mullen Scales of Early Learning, the Communication and Symbolic Behavior Scales Developmental Profile™ and the Ages and Stages Questionnaire, the personal-social subscale.

FINDINGS

At 6 months none of the postural control measures showed statistically significant differences between groups. Infants at high-risk presented significantly lower scores in all behavioral domains than infants at low-risk at 12 months with fair effect sizes. Certain measures of postural control at 6 months could predict language and visual reception behavior at 12 months.

INTERPRETATION

Infants at high-risk for autism spectrum disorder present with delays in social, communication and language behavior as well as altered postural control in the first year of life. The present data support the possibility that motor skills and specifically postural control may drive the development in other domains.

Examining Human Unipedal Quiet Stance: Characterizing Control through Jerk

We investigated the quality of smoothness during human unipedal quiet stance. Smoothness is quantified by the time rate of change of the accelerations, or jerks, associated with the motion of the foot and can be seen as an indicative of how controlled the balance process is. To become more acquainted with this as a quantity, we wanted to establish whether or not it can be modeled as a (stationary) stochastic process and, if so, explore its temporal scaling behavior. Specifically, our study focused on the jerk concerning the center-of-pressure (COP) for each foot. Data were collected via a force plate for individuals attempting to maintain upright posture using one leg (with eyes open). Positive tests for stochasticity allowed us to treat the time series as a stochastic process and, given this, we took the jerk to be proportional to the increment of the force realizations. Detrended fluctuation analysis was the primary tool used to explore the scaling behavior. Results suggest that both the medial-lateral and anterior-posterior components of the jerk display persistent and antipersistent correlations which can be modeled by fractional Gaussian noise over three different temporal scaling regions. Finally, we discussed certain possible implications of these features such as a jerk-based control over the force on the foot's COP.

Sit Still and Pay Attention! Trunk Movement and Attentional Resources in Infants with Typical and Delayed Development

AIMS

(1) examine infant movement during an early posture (sitting) utilizing a novel video assessment technique; and (2) document the differences between infants with typical development (TD), premature infants with motor delay, and infants with cerebral palsy (CP) during focused and nonfocused attention (NFA).

METHODS

Infants were tested when they began to sit independently. We utilized Eulerian Video Magnification (EVM) to accentuate small trunk and pelvic movements for visual coding from video taken during a natural play task with and without focused attention (FA).

RESULTS

Trunk/pelvic movement varied as a function of both motor skill and attention. Infants with TD and CP made fewer trunk movements during periods of FA than NFA. Preterm infants exhibited more trunk/pelvic movement than the other groups and their movement did not differ based on attention type.

CONCLUSIONS

The EVM technique allowed for replicable coding of real-time "hidden" motor adjustments from video. The capacity to minimize extraneous movements in infants, or "sitting still" may allow greater attention to the task at hand, similar to older children and adults. Premature infants' excessive trunk/pelvic movement that did not adapt to task requirements could, in the long term, impact tasks requiring attentional resources.

Children with moderate to severe cerebral palsy may not benefit from stochastic vibration when developing independent sitting

PURPOSE

Determine sitting postural control changes for children with cerebral palsy (CP), using a perceptual-motor intervention and the same intervention plus stochastic vibration through the sitting surface.

METHODS

Two groups of children with moderate or severe CP participated in the 12 week interventions. The primary outcome measure was center of pressure data from which linear and nonlinear variables were extracted and the gross motor function measure (GMFM).

RESULTS

There were no significant main effects of intervention or time or an interaction. Both treatment groups increased the Lyapunov exponent values in the medial-lateral direction three months after the start of treatment as well as their GMFM scores in comparison with baseline.

CONCLUSIONS

The stochastic vibration did not seem to advance the development of sitting postural control in children between the ages of 2 and 6 years. However, perceptual-motor intervention was found beneficial in advancing sitting behavior.

Discriminant ability and criterion validity of the Trunk Impairment Scale for cerebral palsy

Aims: To compare the performance of children with mild and moderate-to-severe cerebral palsy (CP) on the Trunk Impairment Scale (TIS), Gross Motor Function Measure (GMFM), and on center-of-pressure variables; to establish the discriminant ability of these tools to predict severity of motor impairment in CP; and to investigate the criterion validity of the TIS. Methods: Children with mild (n = 18, 11 males, 7 females, mean age = 9.5 ± 2.9 years, Gross Motor Function Classification System I-II) and moderate-to-severe (n = 18, 11 males, 7 females, mean age = 9.2 ± 229, Gross Motor Function Classification System III-IV) CP were tested using the TIS and the GMFM, and during static sitting on force-plate. Results: Children with mild CP showed better trunk (median; 95% confidence interval = 22.5; 21.29-22.59 vs. 13; 11.97-14.8; p < 0.001) and gross motor (60; 57.73-59.3 vs. 40; 38.96-46.25; p < 0.001) scores, and better postural control (lower center of pressure (CoP) displacement [anterior-posterior: (0.42; 0.32-1.11 vs. 0.89; 0.70-1.65; p = 0.022); medial-lateral: (0.42; 0.31-1.08 vs. 0.91; 0.65-1.17; p = 0.044)], and lower area of sway, (0.05; -0.15-0.97 vs. 0.44; 0.23-0.90; p = 0.008) than the moderate-to-severe group. Trunk control and gross motor function explained 81.5% of the variance in the severity of motor condition. Correlations between the TIS and the GMFM were excellent (ρ = 0.944, p < 0.001); correlations between the TIS and CoP variables were low (anterior-posterior displacement: ρ = -0.411, p < 0.05; medial-lateral displacement: ρ = -0.327, p < 0.05); area of sway: ρ = -0.430, p < 0.05; velocity of sway: ρ = -0.308, p < 0.05). Conclusions: The TIS is able to differentiate levels of trunk control across various levels of motor impairments in CP. It is a valid tool to assess trunk control, showing very high concurrent validity with the GMFM sitting dimension. Implications for Rehabilitation Trunk Impairment Scale (TIS) can be used by rehabilitation professionals to differentiate levels of trunk control across levels of motor impairment. TIS showed concurrent validity with Gross Motor Function Measure and should be used to assess trunk control in children with cerebral palsy (CP) in clinical settings. The use of TIS allows a reliable assessment of postural control in children with CP in clinical settings.

Improving Dual-Task Control With a Posture-Second Strategy in Early-Stage Parkinson Disease

OBJECTIVE

To examine the task prioritization effects on postural-suprapostural dual-task performance in patients with early-stage Parkinson disease (PD) without clinically observed postural symptoms.

DESIGN

Cross-sectional study. Participants performed a force-matching task while standing on a mobile platform, and were instructed to focus their attention on either the postural task (posture-first strategy) or the force-matching task (posture-second strategy).

SETTING

University research laboratory.

PARTICIPANTS

Individuals (N=16) with early-stage PD who had no clinically observed postural symptoms.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Dual-task change (DTC; percent change between single-task and dual-task performance) of posture error, posture approximate entropy (ApEn), force error, and reaction time (RT). Positive DTC values indicate higher postural error, posture ApEn, force error, and force RT during dual-task conditions compared with single-task conditions.

RESULTS

Compared with the posture-first strategy, the posture-second strategy was associated with smaller DTC of posture error and force error, and greater DTC of posture ApEn. In contrast, greater DTC of force RT was observed under the posture-second strategy.

CONCLUSIONS

Contrary to typical recommendations, our results suggest that the posture-second strategy may be an effective dual-task strategy in patients with early-stage PD who have no clinically observed postural symptoms in order to reduce the negative effect of dual tasking on performance and facilitate postural automaticity.

Reliability of center of pressure measures for assessing the development of sitting postural control through the stages of sitting

Cerebral palsy (CP) impairs an individual's ability to move and control one's posture. Unfortunately, the signs and symptoms of CP may not be apparent before age two. Evaluating sitting posture is a potential way to assess the developing mechanisms that contribute to CP. The purpose of this project was to determine the reliability of linear and nonlinear measures, including inter- and intrastage reliability, when used to analyze the center of pressure (COP) time series during the stages of sitting development in children with typical development (TD) and with/at-risk for cerebral palsy (CP). We hypothesized that nonlinear tools would be more reliable than linear tools in assessing childrens' sitting development, and reliability would increase with development. COP data was recorded for three trials at eight sessions. Linear parameters used were root mean square, range of sway for the anterior-posterior (AP) and medial-lateral (ML) directions, and sway path. Nonlinear parameters used were Approximate Entropy, the largest Lyapunov Exponent, and Correlation Dimension for the AP and ML direction. Participants consisted of 33 children with TD and 26 children with/at-risk for CP. Our results determined that COP is a moderately reliable method for assessing the development of sitting postural control in stages in both groups. Thus, clinicians may be able to use measures from COP data across stages to assess the efficacy of therapeutic interventions that are intended to improve sitting postural abilities in children with/at-risk for CP.

Saccadic entropy of head impulses in acute unilateral vestibular loss

BACKGROUND/PURPOSE

To evaluate the complexity of vestibular-ocular reflex (VOR) in patients with acute unilateral vestibular loss (AUVL) via entropy analysis of head impulses.

METHODS

Horizontal head impulse test (HIT) with high-velocity alternating directions was used to evaluate 12 participants with AUVL and 16 healthy volunteers. Wireless electro-oculography and electronic gyrometry were used to acquire eye positional signals and head velocity signals. The eye velocity signals were then obtained through differentiation, band-pass filtering. The approximate entropy of eye velocity to head velocity (R_ApEn) was used to evaluate chaos property. VOR gain, gain asymmetry ratio, and R_ApEn asymmetry ratio were also used to compare the groups.

RESULTS

For the lesion-side HIT of the patient group, the mean VOR gain was significantly lower and the mean R_ApEn was significantly greater compared with both nonlesion-side HIT and healthy controls (p < 0.01, one-way analysis of variance). Both the R_ApEn asymmetry ratio and gain asymmetry ratio of the AUVL group were significantly greater compared with those of the control group (p < 0.05, independent sample t test).

CONCLUSION

Entropy and gain analysis of HIT using wireless electro-oculography system could be used to detect the VOR dysfunctions of AUVL and may become effective methods for evaluating vestibular disorders.

Sensor positioning and experimental constraints influence estimates of local dynamic stability during repetitive spine movements

Application of non-linear dynamics analyses to study human movement has increased recently, which necessitates an understanding of how dependent measures may be influenced by experimental design and setup. Quantifying local dynamic stability for a multi-articulated structure such as the spine presents the possibility for estimates to be influenced by positioning of kinematic sensors used to measure spine angular kinematics. Oftentimes researchers will also choose to constrain the spine's movement by physically restraining the pelvis and/or using targets to control movement endpoints. Ten healthy participants were recruited, and asked to perform separate trials of 35 consecutive cycles of spine flexion under both constrained and unconstrained conditions. Electromagnetic sensors that measure three-dimensional angular orientations were positioned over the pelvis and the spinous processes of L3, L1, and T11. Using the pelvic sensor as a reference, each sensor location on the spine was used to obtain a different representation of the three-dimensional spine angular kinematics. Local dynamic stability of each kinematic time-series was determined by calculating the maximum finite-time Lyapunov exponent (λmax). Estimates for λmax were significantly lower (i.e. dynamically more stable) for spine kinematic data obtained from the L3 sensor than those obtained from kinematic data using either the L1 or T11 sensors. Likewise, λmax was lower when the movement was constrained. These results emphasize the importance of proper placement of instrumentation for quantifying local dynamic stability of spine kinematics and are especially relevant for repeated measures designs where data are obtained from the same individual on multiple days.

Abnormal sitting pressures of hemiplegic cerebral palsy children on a school chair

[Purpose] The purpose of this study was to investigate the differences in symmetry of sitting posture between typical developmental (TD) children and hemi-cerebral palsy (CP) children. [Subjects and Methods] A school chair mounted on a force platform was used to assess the quiet-sitting pressure distribution of 10 TD and 10 CP children. [Results] The symmetry index of the TD children was significantly closer to zero than that of the CP children irrespective of the latter group's hemiparetic side. [Conclusions] Sitting posture on school chairs of CP children was more asymmetrical than that of TD children.

Postural control during standing reach in children with Down syndrome

The purpose of the present study was to investigate the dynamic postural control of children with Down syndrome (DS). Specifically, we compared postural control and goal-directed reaching performance between children with DS and typically developing children during standing reach. Standing reach performance was analyzed in three main phases using the kinematic and kinetic data collected from a force plate and a motion capture system. Fourteen children with DS, age and gender matched with fourteen typically developing children, were recruited for this study. The results showed that the demand of the standing reach task affected both dynamic postural control and reaching performance in children with DS, especially in the condition of beyond arm's length reaching. More postural adjustment strategies were recruited when reaching distance was beyond arm's length. Children with DS tended to use inefficient and conservative strategies for postural stability and reaching. That is, children with DS perform standing reach with increased reaction and execution time and decreased amplitudes of center of pressure displacements. Standing reach resembled functional balance that is required in daily activities. It is suggested to be considered as a part of strength and balance training program with graded task difficulty.

Stability of daily home-based measures of postural control over an 8-week period in highly functioning older adults

PURPOSE

The focus of this study was to monitor daily objective measures of standing postural control over an 8-week period, recorded in a person's home, in a population of healthy older adults. Establishing natural patterns of variation in the day-to-day signal, occurring in the relative absence of functional decline or disease, would enable us to determine thresholds for changes in postural control from baseline that could be considered clinically important.

METHODS

Eighteen community-dwelling older adults (3 M, 15 F, 72 ± 6 years) participated in a home-based trial where each day they were asked to complete a technology-enabled routine consisting of a short questionnaire, as well as a quiet standing balance trial. Centre of pressure (COP) excursions were calculated over the course of each daily balance trial to generate variables such as postural sway length and mean sway frequency.

RESULTS

The data demonstrated large differences between subjects in centre of pressure measures (coefficients of variation ranging 37-107 %, depending on the variable). Each participant also exhibited variations in their day-to-day trials (e.g. coefficients of variation across 8 weeks ranging ~17-56 %, within person for mean COP distance). Inter- and intra-subject differences were not strongly related to functional tests, suggesting that these variations were not necessarily aberrant movement patterns, but are seemingly representative of natural movement variability.

CONCLUSIONS

The idea of applying a group-focused approach at an individual level may result in misclassifying important changes for a particular individual. Early detection of deterioration can only be achieved through the creation of individual trajectories for each person, that are inherently self referential.

Trunk Control Ability after Minimally Invasive Lumbar Fusion Surgery during the Early Postoperative Phase

[Purpose] Lumbar fusion has been used for spinal disorders when conservative treatment fails. The minimally invasive approach causes minimal damage to the back muscles and shortens the postoperative recovery time. However, evidence regarding functional recovery in patients after minimally invasive lumbar spinal fusion is limited. The purpose of this study was to investigate how trunk control ability is affected after minimally invasive lumbar fusion surgery during the early postoperative phase. [Subjects and Methods] Sixteen patients and 16 age- and sex-matched healthy participants were recruited. Participants were asked to perform a maximum forward reaching task and were evaluated 1 day before and again 1 month after the lumbar fusion surgery. Center of pressure (COP) displacement, back muscle strength, and scores for the Visual Analog Scale, and Chinese version of the modified Oswestry Disability Index (ODI) were recorded. [Results] The healthy control group exhibited more favorable outcomes than the patient group both before and after surgery in back strength, reaching distance, reaching velocity, and COP displacement. The patient group improved significantly after surgery in all clinical outcome measurements. However, reaching distance decreased, and the reaching velocity as well as COP displacement did not differ before and after surgery. [Conclusion] The LBP patients with lumbar fusion surgery showed improvement in pain intensity 1 month after surgery but no improvement in trunk control during forward reaching. The results provide evidence that the back muscle strength was not fully recovered in patients 1 month after surgery and limited their ability to move their trunk forward.

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.

A Perspective on Human Movement Variability With Applications in Infancy Motor Development

Movement variability is considered essential to typical motor development. However, multiple theoretical perspectives and measurement tools have limited interpretation of the importance of movement variability in biological systems. The complementary use of linear and nonlinear measures have recently allowed for the evaluation of not only the magnitude of variability but also the temporal structure of variability. As a result, the theoretical model of optimal movement variability was introduced. The model suggests that the development of healthy and highly adaptable systems relies on the achievement of an optimal state of variability. Alternatively, abnormal development may be characterized by a narrow range of behaviors, some of which may be rigid, inflexible, and highly predictable or, on the contrary, random, unfocused, and unpredictable. In the present review, this theoretical model is described as it relates to motor development in infancy and specifically the development of sitting posture.

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.

Kinematic assessment of stereotypy in spontaneous movements in infants

Movement variation constitutes a crucial feature of infant motor development. Reduced variation of spontaneous infant movements, i.e. stereotyped movements, may indicate severe neurological deficit at an early stage. Hitherto evaluation of movement variation has been mainly restricted to subjective assessment based on observation. This article introduces a method for quantitative assessment yielding an objective definition of stereotyped movements which may be used for the prognosis of neurological deficits such as cerebral palsy (CP). Movements of 3-month-old infants were recorded with an electromagnetic tracking system facilitating the analysis of joint angles of the upper and lower limb. A stereotypy score based on dynamic time warping has been developed describing movements which are self-similar in multiple degrees of freedom. For clinical evaluation, this measure was calculated in a group of infants at risk for neurological disorders (n=54) and a control group of typically developing children (n=21) on the basis of spontaneous movements at the age of 3 months. The stereotypy score was related to outcome at the age of 24 months in terms of CP (n=10) or no-CP (n=53). Using the stereotypy score of upper limb movements CP cases could be identified with a sensitivity of 90% and a specificity of 96%. The corresponding score of the leg movements did not allow for valid discrimination of the groups. The presented stereotypy feature is a promising candidate for a marker that may be used as a simple and noninvasive quantitative measure in the prediction of CP. The method can be adopted for the assessment of infant movement variation in research and clinical applications.

Human movement variability, nonlinear dynamics, and pathology: is there a connection?

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 concept of variability and the measures for nonlinear dynamics used to evaluate this concept open new vistas for research in movement dysfunction of many types. This review describes innovations in the exploration of variability and their potential importance in understanding human movement. Far from being a source of error, evidence supports the presence of an optimal state of variability for healthy and functional movement. This variability has a particular organization and is characterized by a chaotic structure. Deviations from this state can lead to biological systems that are either overly rigid and robotic or noisy and unstable. Both situations result in systems that are less adaptable to perturbations, such as those associated with unhealthy pathological states or absence of skillfulness.

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.

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.