Learning about gravity: segmental assessment of upright control as infants develop independent sitting

An update of the development of motor behavior

This primer describes research on the development of motor behavior. We focus on infancy when basic action systems are acquired-posture, locomotion, manual actions, and facial actions-and we adopt a developmental systems perspective to understand the causes and consequences of developmental change. Experience facilitates improvements in motor behavior and infants accumulate immense amounts of varied everyday experience with all the basic action systems. At every point in development, perception guides behavior by providing feedback about the results of just prior movements and information about what to do next. Across development, new motor behaviors provide new inputs for perception. Thus, motor development opens up new opportunities for acquiring knowledge and acting on the world, instigating cascades of developmental changes in perceptual, cognitive, and social domains. This article is categorized under: Cognitive Biology > Cognitive Development Psychology > Motor Skill and Performance Neuroscience > Development.

The relationship between segmental trunk control and gross motor performance in low birth weight born infants

OBJECTIVE

Trunk control is associated with gross motor development. This study examines the relationship between segmental trunk control and gross motor performance in low birth weight (LBW) infants.

METHODS

A total of 42 LBW infants and 43 normal birth weight (NBW) infants aged 3-9 months were sampled for this cross-sectional study. All infants were evaluated one time by the Segmental Assessment Trunk Control (SATCo) and the Alberta Infant Motor Scale (AIMS).

RESULTS

Statistically high and significant correlations were found between gross motor performance and segmental trunk control in all sample populations (r = 0.835; p = .001). No statistically significant difference was found regarding the segmental trunk control between the groups (p = .119). The LBW infants with atypical motor development had poorer trunk control than the LBW infants with typical development (f = 5.480; p = .001).

CONCLUSION

Our results show that LBW infants with atypical motor development had poorer trunk control than LBW infants with typical motor development. It was found that the segmental trunk controls of LBW infants were 0.398 times lower than in NBW infants.

Controlling posture to see the world: The integration of visual task demands and postural sway in sitting and standing infants

Our ability to integrate posture with visually demanding tasks is a critical aspect of motor behavior flexibility. When looking at a small object, excessive body movements impair an individual's ability to visually attend to the object. To overcome this problem, we adjust our postural sway to successfully focus on the object. The goal of the current study was to assess whether infants also adjust postural sway when engaged in a challenging visual task. The participants, 19 independently sitting infants (Sitters) and 21 newly independently standing infants (Standers), sat or stood on a force plate while viewing differently sized images displayed on a monitor (smaller images: 8 × 6.5 cm or 3 × 3 cm; larger images: 13 × 16 cm or 13 × 13 cm). Regardless of image size, Standers were less stable than Sitters with larger sway areas and faster sway velocities. Both Sitters and Standers adjusted sway area but not sway velocity, based on image size. Sitters and Standers differed in how they controlled sway dynamics. Standers but not Sitters altered sway dynamics based on image size. Overall, infants used posture-specific adaptive control strategies to make fine-grained adjustments based on image size. The development of the ability to integrate posture with a visually demanding task further emphasizes the capability of advanced complex motor behaviors during infancy, enabling infants to flexibly attend to important aspects of their environment at different postural positions.

Predicting Age of Independent Walking in Preterm Infants: A Longitudinal Study Using Neonatal Characteristics and Motor Development Variables

OBJECTIVE

To formulate an equation estimating months to independent walking in moderate to late preterm infants based on neonatal characteristics and gross motor development from 7 months to independent walking.

METHODS

Sixty infants born between 32 to 36 weeks were assessed using Alberta Infant Motor Scale (AIMS) for gross motor development. Neonatal characteristics were recorded at 7 months, and caregiver-reported independent walking onset. Pearson correlation analyzed age, AIMS scores, and neonatal factors. Multiple regression developed the prediction equation.

RESULTS

The equation for independent walking onset, which included gestational age (GA) at birth, total AIMS score at 10 months of age (10th AIMS), and birth head circumference (BHC), exhibited a strong correlation (r=0.707) and had a predictive power of 50.0%. The equation is as follows: age onset of independent walking (months)=33.157, -0.296 (GA), -0.132 (10th AIMS), -0.196 (BHC), with an estimation error of 0.631 months.

CONCLUSION

Neonatal characteristics, such as GA, 10th AIMS, and BHC, are key determinants in estimating the onset of independent walking in moderate to late preterm infants.

Infant Sitting and Multi-Directional Reaching Skill

We tested twenty-one 6- to 10-month-old infants with a wide range of sitting experience in forward and rightward reaching during unsupported sitting on the floor. Sessions were video-recorded for further behavioral and machine learning-based kinematic analyses. All infants, including novice sitters, successfully touched and grasped toys in both directions. Infant falls, hand support, and base of support changes were rare. Infants with more sitting experience showed better upright posture than novice sitters. However, we found no differences in trunk displacement or reaching kinematics between directions or across sitting experience. Thus, multi-directional reaching is functional in both novice and experienced infant sitters. We suggest that trunk and arm stability in sagittal and frontal planes is integral to learning to sit.

Learning to Move in a Changing Body in a Changing World

Infants of all species learn to move in the midst of tremendous variability and rapid developmental change. Traditionally, researchers consider variability to be a problem for development and skill acquisition. Here, we argue for a reconsideration of variability in early life, taking a developmental, ecological, systems approach. Using the development of walking in human infants as an example, we argue that the rich, variable experiences of infancy form the foundation for flexible, adaptive behavior in adulthood. From their first steps, infants must cope with changes in their bodies, skills, and environments. Rapid growth spurts and a continually expanding environment of surfaces, elevations, and obstacles alter the biomechanical constraints on balance and locomotion from day to day and moment to moment. Moreover, infants spontaneously generate a variable practice regimen for learning to walk. Self-initiated locomotion during everyday activity consists of immense amounts of variable, time-distributed, error-filled practice. From infants' first steps and continuing unabated over the next year, infants walk in short bursts of activity (not continual steps), follow curved (not straight) paths, and take steps in every direction (not only forward)-all the while, accompanied by frequent falls as infants push their limits (rather than a steady decrease in errors) and explore their environments. Thus, development ensures tremendous variability-some imposed by physical growth, caregivers, and a changing environment outside infants' control, and some self-generated by infants' spontaneous behavior. The end result of such massive variability is a perceptual-motor system adept at change. Thus, infants do not learn fixed facts about their bodies or environments or their level of walking skill. Instead, they learn how to learn-how to gauge possibilities for action, modify ongoing movements, and generate new movements on the fly from step to step. Simply put, variability in early development is a feature, not a bug. It provides a natural training regimen for successfully navigating complex, ever-changing environments throughout the lifespan. Moreover, observations of infants' natural behavior in natural, cluttered environments-rather than eliciting adult-like behaviors under artificial, controlled conditions-yield very different pictures of what infants of any species do and learn. Over-reliance on traditional tasks that artificially constrain variability therefore risks distorting researchers' understanding of the origins of adaptive behavior.

Study protocol for a randomised controlled trial to determine the efficacy of an intensive seated postural intervention delivered with robotic and rigid trunk support systems

INTRODUCTION

Children with cerebral palsy (CP) classified as gross motor function classification system (GMFCS) levels III-IV demonstrate impaired sitting and reaching control abilities that hamper their overall functional performance. Yet, efficacious interventions for improving sitting-related activities are scarce. We recently designed a motor learning-based intervention delivered with a robotic Trunk-Support-Trainer (TruST-intervention), in which we apply force field technology to individualise sitting balance support. We propose a randomised controlled trial to test the efficacy of the motor intervention delivered with robotic TruST compared with a static trunk support system.

METHODS AND ANALYSIS

We will recruit 82 participants with CP, GMFCS III-IV, and aged 6-17 years. Randomisation using concealed allocation to either the TruST-support or static trunk-support intervention will be conducted using opaque-sealed envelopes prepared by someone unrelated to the study. We will apply an intention-to-treat protocol. The interventions will consist of 2 hours/sessions, 3/week, for 4 weeks. Participants will start both interventions with pelvic strapping. In the TruST-intervention, postural task progression will be implemented by a progressive increase of the force field boundaries and then by removing the pelvic straps. In the static trunk support-intervention, we will progressively lower the trunk support and remove pelvic strapping. Outcomes will be assessed at baseline, training midpoint, 1-week postintervention, and 3-month follow-up. Primary outcomes will include the modified functional reach test, a kinematic evaluation of sitting workspace, and the Box and Block test. Secondary outcomes will include The Segmental Assessment of Trunk Control test, Seated Postural & Reaching Control test, Gross Motor Function Measure-Item Set, Canadian Occupational Performance Outcome, The Participation and Environment Measure and Youth, and postural and reaching kinematics.

ETHICS AND DISSEMINATION

The study was approved by the Columbia University Institutional Review Board (AAAS7804). This study is funded by the National Institutes of Health (1R01HD101903-01) and is registered at clinicaltrials.gov.

TRIAL REGISTRATION NUMBER

NCT04897347; clinicaltrials.gov.

Dynamic sitting in infants: Limits of stability

BACKGROUND

Limits of stability-defined by the maximum distances a person is willing to reach without falling or changing the base of support-are measures of dynamic balance.

RESEARCH QUESTION

What are infants' sitting stability limits in the forward and right directions?

METHODS

Twenty-one 6- to 10-month old infants participated in this cross-sectional study. To incentivize infants to reach beyond arm's length, caregivers began by holding a toy close to their infants at shoulder height. Caregivers then moved the toy farther away as infants tried to reach for it until infants lost balance, placed their hands on the floor, or transitioned out of sitting. All sessions were conducted via Zoom™ and video-recorded for further analyses using DeepLabCut for 2D pose estimation and Datavyu to determine timings of the reach and to code infants' postural behaviors.

RESULTS

Infants' trunk excursions in the anterior-posterior plane (for forward reaches) and medio-lateral plane (for rightward reaches) represented their stability limits. Most infants ended the reach by returning to their original sitting position; however, infants with higher Alberta Infant Motor Scale (AIMS) scores transitioned out of sitting and infants with lower AIMS scores sometimes fell (mostly during rightward reaching). Trunk excursions were correlated with months of sitting experience. Rightward trunk excursions were also correlated with AIMS scores and age. Overall, infants' trunk excursions were larger in the forward than in the right direction, and such discrepancy was consistent across infants. Lastly, the more often infants adopted movement strategies with their legs (e.g., bending the knees), the greater the trunk excursion they attained.

SIGNIFICANCE

Sitting control entails learning to perceive the boundaries of stability limits and acquiring anticipatory postures to suit the needs of the task. Tests and interventions that target sitting stability limits could be beneficial for infants with or at risk of motor delays.

Quantifying States and Transitions of Emerging Postural Control for Children Not Yet Able to Sit Independently

Objective, quantitative postural data is limited for individuals who are non-ambulatory, especially for those who have not yet developed trunk control for sitting. There are no gold standard measurements to monitor the emergence of upright trunk control. Quantification of intermediate levels of postural control is critically needed to improve research and intervention for these individuals. Accelerometers and video were used to record postural alignment and stability for eight children with severe cerebral palsy aged 2 to 13 years, under two conditions, seated on a bench with only pelvic support and with additional thoracic support. This study developed an algorithm to classify vertical alignment and states of upright control; Stable, Wobble, Collapse, Rise and Fall from accelerometer data. Next, a Markov chain model was created to calculate a normative score for postural state and transition for each participant with each level of support. This tool allowed quantification of behaviors previously not captured in adult-based postural sway measures. Histogram and video recordings were used to confirm the output of the algorithm. Together, this tool revealed that providing external support allowed all participants: (1) to increase their time spent in the Stable state, and (2) to reduce the frequency of transitions between states. Furthermore, all participants except one showed improved state and transition scores when given external support.

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.

Factors Associating with the Segmental Postural Control during Sitting in Moderate-to-Late Preterm Infants via Longitudinal Study

(1) Background: biological variables and particular child rearing practices could be linked to postural control and rates of sitting onset. The segmental Assessment of Trunk Control (SATCo) is currently used as an assessment of postural control with a specific segment on premature infants. However, the association between related factors and segmental trunk control during sitting development in preterm infants via longitudinal assessments is still limited. Objective: to investigate the associations between biological and child rearing factors and segmental trunk control during sitting in moderate to late premature birth from the age of 4 months to age of independent sitting attainment. (2) Methods: forty-two infants born between 32 and 36 weeks of gestation were recruited. Their segmental trunk control was assessed using the SATCo. Their related factors were recorded from the age of 4 months to early onset of independent sitting attainment. The generalised estimating equation (GEE) model was used to identify the association between related factors and the SATCo with a linear distribution. (3) Results: cause of prematurity, baby rocking recliner and baby walker usage were negative factors, while play in a sitting position, opportunity to move on a traditional mat and sleep mattress were positive factors contributing to the segmental control of the trunk. (4) Conclusions: the experience of sitting on different surfaces and an opportunity to sit without support during the child rearing period from age of 4 months corrected could be positive factors associating with the segmental trunk control in moderate-to-late premature infants.

Segmental Assessment of Trunk Control in Moderate-to-Late Preterm Infants Related to Sitting Development

(1) Background: The assessment of postural segment control in premature infants seems to be critical during the onset of upright gross motor development, especially sitting. Identifying correlations between postural segment control and the development of sitting milestones could help with promoting optimal gross motor movement. However, data on this topic in home-raised premature infants via longitudinal design are still limited. The purpose of this study was to examine relationships between postural segment control and sitting development through series assessments from the corrected age of 4 months until the early onset of independent sitting attainment. (2) Methods: 33 moderate-to-late premature infants were recruited. Their trunk segment control was assessed using the Segmental Assessment of Trunk Control (SATCo), and sitting development was examined by the Alberta Infant Motor Scale (AIMS). Relationships between SATCo and sitting scores were analysed using Spearman’s rank correlation (r_s). (3) Results: significant fair-to-good correlations between segmental trunk control and sitting scales were found from 4 months (r_s = 0.370–0.420, p < 0.05) to the age of independent sitting attainment (r_s = 0.561–0.602, p < 0.01). (4) Conclusion: relationships between the trunk segment control and sitting ability of moderate-to-late preterm infants were increased in accordance with age.

Postural mechanisms in moderate-to-severe cerebral palsy

People with moderate-to-severe cerebral palsy (CP) have the greatest need for postural control research yet are usually excluded from research due to deficits in sitting ability. We use a support system that allows us to quantify and model postural mechanisms in nonambulatory children with CP. A continuous external bench tilt stimulus was used to evoke trunk postural responses in seven sitting children with CP (ages 2.5 to 13 yr) in several test sessions. Eight healthy adults were also included. Postural sway was analyzed with root mean square (RMS) sway and RMS sway velocity, along with frequency response functions (FRF, gain and phase) and coherence functions across two different stimulus amplitudes. A feedback model (including sensorimotor noise, passive, reflexive, and sensory integration mechanisms) was developed to hypothesize how postural control mechanisms are organized and function. Experimental results showed large RMS sway, FRF gains, and variability compared with adults. Modeling suggested that many subjects with CP adopted "simple" control with major contributions from a passive and reflexive mechanism and only a small contribution from active sensory integration. In contrast, mature trunk postural control includes major contributions from sensory integration and sensory reweighting. Relative to their body size, subjects with CP showed significantly lower damping, three to five times larger corrective torque, and much higher sensorimotor noise compared with the healthy mature system. Results are the first characterization of trunk postural responses and the first attempt at system identification in moderate-to-severe CP, an important step toward developing and evaluating more targeted interventions.NEW & NOTEWORTHY Cerebral palsy (CP) is the most common cause of motor disability in children. People with moderate-to-severe CP are typically nonambulatory and have major impairments in trunk postural control. We present the first systems identification study to investigate postural responses to external stimulus in this population and hypothesize at how the atypical postural control system functions with use of a feedback model. People with moderate-to-severe CP may use a simple control system with significant sensorimotor noise.

Longitudinal Development of Segmental Trunk Control in Full Term and Preterm Infants- a Pilot Study: Part I

Purpose: No previous study examined trunk control development in preterm infants. The present study examined the longitudinal development of segmental trunk control from 4 to 12 months of (corrected) age in preterm infants in comparison with full-term infants.Methods: Thirty-one preterm infants and 30 full-term infants were recruited. All infants were tested monthly using the Segmental Assessment of Trunk Control and the Alberta Infant Motor Scale at 4, 8 and 12 months of age.Results: Segmental trunk control development was significantly delayed in the preterm infants. Statistically significant positive correlations were found between trunk control status and gross motor skills.Conclusion: This was first study showing that segmental trunk control development was significantly different in preterm infants. Segmental trunk control and gross motor performance were coupled in young infants. A dual focus on training upright trunk control and specific motor skills may maximise therapy outcomes for infants with motor delay.

How Has Electromyography Been Used to Assess Reaching in Infants? A Systematic Review

The aims of this systematic review were: to investigate the use of surface electromyography in the assessment of reaching in infants; to assess the usefulness of this tool to the assessment of reaching, and its parameters and limitations; to assess the methodological quality of the studies available in the literature. The search in the databases MEDLINE, SciELO, LILACS, Embase, PEDro, Cochrane, and EBSCO resulted in 5 selected studies. The studies aimed to elucidate how muscle behavior occurs in the development of reaching. The lack of standardized recommendations for the use of EMG in infants limit the reproducibility and comparison between studies. There are challenges and limitations regarding the use of electromyography in infants, which are caused by peculiarities inherent to the development of the neuromotor and musculoskeletal systems.

Electromyographic activity of head and trunk muscles in newborns

Abstract Introduction: The electric activity of muscles can be assessed using electromyography to determine their function and help identify possible delays in motor development. Objective: Determine the amplitude of the electromyographic activity of the head and trunk flexor and extensor muscles of term and preterm newborns. Method: This is a longitudinal pilot study where 20 preterm and 20 term newborns admitted to the Prof. Fernando Figueira Institute of Comprehensive Medicine were assessed. All the newborns were evaluated between 24 and 72 hours after delivery, with the premature children assessed a second time when term equivalent age was reached at 40 weeks. Data were recorded using a surface electromyograph and the electrodes were attached to the muscle bellies of the sternocleidomastoid, upper portion of the trapezius, rectus abdominis and erector spinae muscles. Results: Comparison of the electromyographic activity between the preterm newborns showed significantly higher values in all the muscles when the group reached term equivalent age. Additionally, the electromyographic activity of the term group was greater than that obtained by the preterm newborns. Conclusion: With advancing age and maturation of the physiological systems, including the muscle system, preterm newborns tend to exhibit a similar muscle activation behavior to that of the term infants, resulting in better motor development.

Relationship between segmental trunk control and gross motor development in typically developing infants aged from 4 to 12 months: a pilot study

Background

Trunk control is generally considered to be related to gross motor development. However, this assumption has not been validated with clinical data. This pilot study was the first of its kind to examine the longitudinal development of segmental trunk control and gross motor development from 4 to 12 months of age in typically developing full-term infants.

Methods

A convenience cohort of 20 healthy full-term infants (mean gestation = 39.0 weeks, SD 1.2; mean birthweight = 2975.0 g, SD 297.0; males = 10) was recruited. All study infants were tested and scored monthly by independent assessors using the Segmental Assessment of Trunk Control and the Alberta Infant Motor Scale from 4 to 12 months of age.

Results

A developmental trend of segmental trunk control was found in the infants. Static vertical upright trunk control developed prior to active and reactive control. Statistically significant correlations were found between trunk control status and gross motor development mainly in prone and sitting positions from 8 months of age onwards (all p < 0.004, Spearman’s r ranged from 0.644 to 0.798).

Conclusions

This pilot study provides preliminary clinical evidence to support the inter-dependency between vertical upright trunk control and gross motor development in young infants, particularly as upright functional skills are gained. This suggests that a dual focus on training upright trunk control alongside gross motor skills could be of benefit in the treatment of infants with movement disorders.

Infants plan prehension while pivoting

Skilled object retrieval requires coordination of the perceptual and motor systems. Coordination is especially challenging when body position is changing and visual search is required to locate the target. In three experiments, we used a "pivot paradigm" to induce changes in body position: Participants were passively pivoted 180° toward a target placed at varied locations to the left and right of the center of a reaching board. Experiment 1 showed that 6- to 15-month-old infants (n = 41) plan prehension so quickly that they retrieve targets mid-turn and scale their reaches to target location relative to turn direction. Experiment 2 characterized planning mid-turn reaching in 6- to 8-month-olds (n = 5) wearing a head-mounted eye tracker. Reach planning depended on when the target appeared in the field of view-not on target fixation. Experiment 3 used head-mounted eye tracking and motion tracking to assess perceptual-motor coordination in adults (n = 13). Adults displayed more mid-turn reaching than infants. But like infants, adults scaled reaching to target location relative to turn direction, and contact time depended on when the target came into view-not on target fixation. Findings show that fast, efficient perceptual-motor coordination supports flexibility in infant prehension, and constraints on coordination are similar across the lifespan.

Sensitivity to change and responsiveness of the Segmental Assessment of Trunk Control (SATCo) in children with spinal cord injury

PURPOSE

The purpose of this study was to assess the sensitivity and responsiveness of the Segmental Assessment of Trunk Control (SATCo) for evaluating trunk control in children with spinal cord injury (SCI) receiving activity-based locomotor training (AB-LT).

METHODS

Prospective study of nine outcomes for consecutively enrolled children in outpatient AB-LT. To evaluate sensitivity to change, linear-mixed models were constructed and adjusted for covariates: age at and time since SCI. To evaluate responsiveness, standardized response means and 95% confidence intervals were estimated per outcome.

RESULTS

SATCo scores increased significantly (p < 0.05) regardless of chronicity, initial score, and injury level. The SATCo was the most responsive measure and the only outcome demonstrating a large effect size after 3 months of therapy.

CONCLUSIONS

Children with SCI receiving AB-LT improved trunk control regardless of chronicity, initial impairment, or prior experience. SATCo sensitivity and responsiveness support its usefulness in measuring trunk control in children with SCI.

Motor Development: Embodied, Embedded, Enculturated, and Enabling

Motor development and psychological development are fundamentally related, but researchers typically consider them separately. In this review, we present four key features of infant motor development and show that motor skill acquisition both requires and reflects basic psychological functions. ( a) Motor development is embodied: Opportunities for action depend on the current status of the body. ( b) Motor development is embedded: Variations in the environment create and constrain possibilities for action. ( c) Motor development is enculturated: Social and cultural influences shape motor behaviors. ( d) Motor development is enabling: New motor skills create new opportunities for exploration and learning that instigate cascades of development across diverse psychological domains. For each of these key features, we show that changes in infants' bodies, environments, and experiences entail behavioral flexibility and are thus essential to psychology. Moreover, we suggest that motor development is an ideal model system for the study of psychological development.

Working towards an objective segmental assessment of trunk control in children with cerebral palsy

BACKGROUND

Physical therapy evaluations of motor control are currently based on subjective clinical assessments. Despite validation, these can still be inconsistent between therapists and between clinics, compromising the process of validating a therapeutic intervention and the subsequent generation of evidence-based practice (EBP) guidelines. EBP benefits from well-defined objective measurements that complement existing subjective assessments.

RESEARCH QUESTION

The aim of this study was to develop an objective measure of head/trunk control in children with Cerebral Palsy (CP) using previously developed video-based methods of head/trunk alignment and absence of external support and compare these with the existing subjective Segmental Assessment of Trunk Control (SATCo).

METHODS

Twelve children with CP were recruited and an average of 3 (±1.1) SATCo tests performed per child. The full SATCo was concurrently video-recorded from a sagittal view; markers were placed on specific landmarks of the head, trunk and pelvis to track and estimate head/trunk segment position. A simplified objective rule was created for control and used on videos showing no external support. This replicated the clinical parameters and enabled identification of the segmental-loss-of-control. The subjectively and objectively identified segmental-loss-of-control were compared using a Pearson Correlation Coefficient.

RESULTS

An angular-threshold of 17° from alignment showed the minimum bias between the subjectively and the objectively measured segmental-loss-of-control (mean error =-0.11 and RMSE = 1.5) and a significant correlation (r = 0.78, r² = 0.61, p < .01).

SIGNIFICANCE

This study showed that simple objective video-based measurements can be used to reconstruct the subjective assessment of segmental head/trunk control. This suggests that a clinically-friendly video-based objective measure has future potential to complement subjective assessments and to assist in the generation of EBP guidelines. Further development will increase the information that can be extracted from video images and enable generation of a fully automated objective measure.

Targeted Training in Managing Children With Poor Trunk Control: 4 Case Reports

PURPOSE

This study investigated whether targeted training was feasible with young children younger than 2 years with poor trunk control due to cerebral palsy or developmental delay without using specialized equipment and the overall change in trunk control and functional ability, with the addition of targeted training to standard care physical therapy.

SUMMARY OF KEY POINTS

Four children younger than 24 months with motor disorders were recruited. No difficulty was identified in using targeted training with this group. Within 3 months of commencing intervention, the 4 children had increased trunk control and functional abilities including independent sitting and bilateral hand use in play.

CONCLUSIONS AND RECOMMENDATIONS FOR CLINICAL PRACTICE

This form of targeted training was feasible for young children with motor disorders and augmented standard care therapy in enhancing both trunk control and motor skills. Targeted training should be further investigated as a potentially effective treatment.

Parent handling of typical infants varies segmentally across development of postural control

Although trunk muscles extend across multiple vertebral joints, recent motor control studies have shown that a top-down progression of trunk control in typical infants occurs incrementally, one segment at a time, until independent sitting. The current study merges this surprising developmental pattern with parent behavior by exploring the relationship between how parents hold their infant and the segmental level for which the infant exhibits postural control. We measured trunk control of 60 infants (1-8 months) via the segmental assessment of trunk control. Spontaneous parental hold and variability was recorded during repeated sitting and standing conditions. Parent hold correlated with infant level of control in both sitting and standing, providing evidence for a positive interaction between parent behavior and segmental trunk development.

Influence of Sitting Positions and Level of Trunk Control During Reaching Movements in Late Preterm and Full-Term Infants

In order to acquire reaching and independent sitting, refinement of trunk control is needed by gradually and progressively incorporating the head, thoracic, lumbar, and sacral segments. Previous studies have evaluated trunk control in a segmental way, standardizing the level of manual support in the infants' trunk during reaching. The aim of this study was to identify the level of trunk control and to analyze the influence of the difference sitting positions in late preterm and full-term infants between 6 and 8 months of age during reaching. Therefore, 36 infants born full term (control group)-FTG and 20 late preterm infants at a corrected age (experimental group)-PTG were evaluated. Most of the infants started the study at 6 months and they were evaluated monthly until 8 months of age (longitudinal study) in a total of 1-3 visits. The Segmental Assessment of Trunk Control was used to identify the level of trunk control in a segmental way, as well as to verify the capacity of the infant to maintain or regain the vertical position while sitting. Kinematic analysis was used for reaching. The infants were in a ring sitting position and at 90° of flexion. To elicit reaching, an attractive object was presented at the infant's midline and at 45° to the right and left. We found that PTG infants presented lower trunk control scores, i.e., worse control. For both groups, the ring sitting position and at 90° of flexion did not influence most kinematic variables during reaching because accurate manual support was provided for the infants' trunk. The PTG group presented less trunk displacement when at 90° of flexion. Compared to the FTG, even with accurate trunk support, the PTG group presented more immature reaches. These results suggest that accurate manual trunk support favored more stability of the trunk during the reach. Thus, early intervention is suggested for PTG infants and reaching in this age group should be trained in the ring sitting position with their trunk accurately manually supported. SATCo is an effective tool for segmental trunk evaluation.

Behavioral flexibility in learning to sit

What do infants learn when they learn to sit upright? We tested behavioral flexibility in learning to sit-the ability to adapt posture to changes in the environment-in 6- to 9-month-old infants sitting on forward and backward slopes. Infants began with slant at 0°; then slant increased in 2° increments until infants lost balance. Infants kept balance on impressively steep slopes, especially in the forward direction, despite the unexpected movements of the apparatus. Between slant adjustments while the slope was stationary, infants adapted posture to the direction and degree of slant by leaning backward on forward slopes and forward on backward slopes. Postural adaptations were nearly optimal for backward slopes. Sitting experience predicted greater postural adaptations and increased ability to keep balance on steeper changes of slant, but only for forward slopes. We suggest that behavioral flexibility is integral to learning to sit and increases with sitting experience.

The potential of an automated system to identify the upper limb component of a controlled sitting posture

Full trunk control in sitting is demonstrated only when the head-trunk are aligned and upper limbs remain free of contact from mechanical support. These components represent a Controlled Kinetic Chain and can be evaluated in people with neuromotor disability using the Segmental Assessment of Trunk Control (SATCo) when a therapist provides manual trunk support at different segmental levels. However, the SATCo, as with other clinical assessments of control, is subjective. The SATCo was translated to objective rules relating the position of the hands and elbows to the head-trunk and then tested to determine the extent to which this automated objective method replicated the clinical judgement. Clinical evaluation used video to determine whether the upper limb was free of mechanical support while the objective evaluation used 3D motion capture of the trunk and upper limbs with a classification rule. The agreement between clinical and objective classification was calculated for three conditions of a distance-from-support-surface threshold parameter in five healthy adults and five children with cerebral palsy. The unfitted (zero-threshold values) method replicated the clinical judgement in part (68.26%±15.7, adults, 48.3%±33.9 children). The fitted (level-of-support determined) agreement showed that the process could be refined using trial specific parameters (88.32%±5.3 adults, 89.84%±10.2 children). The fixed-values agreement showed high values when using general group parameters (80.80%±3.1 adults, 74.31%±21.5 children). This objective classification of the upper limb component of trunk control largely captures the clinical evaluation. It provides the first stages in development of a clinically-friendly fully automated method.

The Impact of Segmental Trunk Support on Posture and Reaching While Sitting in Healthy Adults

The authors investigated postural and arm control in seated reaches while providing trunk support at midribs and pelvic levels in adults. Kinematics and electromyography of the arm and ipsiliateral and contralateral paraspinal muscles were examined before and during reaching. Kinematics remained constant across conditions, but changes were observed in neuromuscular control. With midribs support, the ipsilateral cervical muscle showed either increased anticipatory activity or earlier compensatory muscle responses, suggesting its major role in head stabilization. The baseline activity of bilateral lumbar muscles was enhanced with midribs support, whereas with pelvic support, the activation frequency of paraspinal muscles increased during reaching. The results suggest that segmental trunk support in healthy adults modulates ipsilateral or contralateral paraspinal activity while overall kinematic outputs remain invariant.

Effect of Biomechanical Constraints on Neural Control of Head Stability in Children With Moderate to Severe Cerebral Palsy

BACKGROUND

External support has been viewed as an important biomechanical constraint for children with deficits in postural control. Nonlinear analysis of head stability may be helpful to confirm benefits of interaction between external trunk support and level of trunk control.

OBJECTIVE

The purpose of this study was to compare the effect of biomechanical constraints (trunk support) on neural control of head stability during development of trunk control.

DESIGN

This was a quasi-experimental repeated-measures study.

METHODS

Data from 15 children (4-16 years of age) with moderate (Gross Motor Function Classification System [GMFCS] IV; n=8 [4 boys, 4 girls]) or severe (GMFCS V; n=7 [4 boys, 3 girls]) cerebral palsy (CP) were compared with previous longitudinal data from infants with typical development (TD) (3-9 months of age). Kinematic data were used to document head sway with external support at 4 levels (axillae, midrib, waist, and hip). Complexity, predictability, and active degrees of freedom for both anterior-posterior and medial-lateral directions were assessed.

RESULTS

Irrespective of level of support, CP groups had lower complexity, increased predictability, and greater degrees of freedom. The effect of support differed based on the child's segmental level of control. The GMFCS V and youngest TD groups demonstrated better head control, with increased complexity and decreased predictability, with higher levels of support. The GMFCS IV group had the opposite effect, showing decreased predictability and increased complexity and degrees of freedom with lower levels of support.

LIMITATIONS

Infants with typical development and children with CP were compared based on similar segmental levels of trunk control; however, it is acknowledged that the groups differed for age, cognitive level, and motor experience.

CONCLUSIONS

The effect of external support varied depending on the child's level of control and diagnostic status. Children with GMFCS V and young infants with TD had better outcomes with external support, but external support was not enough to completely correct for the influence of CP. Children with GMFCS IV performed worse, with increased predictability and decreased complexity, when support was at the axillae or midribs, suggesting that too much support can interfere with postural sway quality.

Versão brasileira da Segmental Assessment of Trunk Control (SATCo)

RESUMO Traduziu-se e adaptou-se para o português do Brasil o teste Segmental Assessment of Trunk Control (SATCo). Dois profissionais proficientes na língua inglesa traduziram, independentemente, a escala original para o português do Brasil (T1 e T2). Em seguida, gerou-se a versão traduzida de consenso (TU). Dois tradutores realizaram duas versões em inglês (RT1 e RT2) da versão TU. Um novo processo de consenso entre tradutores e pesquisadores resultou em uma versão em inglês (RTfinal), que foi comparada com a versão original, com vistas a possíveis diferenças semânticas. A versão do instrumento em português do Brasil (TU), denominada “Avaliação Segmentar do Controle de Tronco”, foi revisada pela comissão de especialistas, composta por três fisioterapeutas, para verificação do conteúdo e gerou a segunda versão de concordância (Tfinal). Tfinal foi encaminhada a uma das autoras da escala original para verificar o entendimento da versão em português do Brasil. Após essa etapa, 20 fisioterapeutas aplicaram a escala em crianças com paralisia cerebral. Parte dos fisioterapeutas indica a necessidade de complementação de informação na descrição das instruções e na descrição da pontuação.

The development of motor behavior

This article reviews research on the development of motor behavior from a developmental systems perspective. We focus on infancy when basic action systems are acquired. Posture provides a stable base for locomotion, manual actions, and facial actions. Experience facilitates improvements in motor behavior and infants accumulate immense amounts of experience with all of their basic action systems. At every point in development, perception guides motor behavior by providing feedback about the results of just prior movements and information about what to do next. Reciprocally, the development of motor behavior provides fodder for perception. More generally, motor development brings about new opportunities for acquiring knowledge about the world, and burgeoning motor skills can instigate cascades of developmental changes in perceptual, cognitive, and social domains. WIREs Cogn Sci 2017, 8:e1430. doi: 10.1002/wcs.1430 For further resources related to this article, please visit the WIREs website.

Segmental trunk and head dynamics during frontal plane tilt stimuli in healthy sitting adults

A more detailed understanding of trunk behavior during upright sitting is needed to create a foundation to address functional posture impairments. Therefore, we characterized the dynamics of the trunk and head during perturbed sitting. A three-link inverted pendulum model of head and trunk segments was used to analyze kinematics of eight healthy sitting adults. Magnetic sensors were placed at the head and two locations of the trunk (C7 and T7). Six surface tilt stimuli (two spontaneous sway tests [no surface stimulus; eyes open, EO/eyes closed, EC] and four tests with continuous pseudorandom surface tilts [2 peak-to peak amplitudes of 2° or 8°; EO/EC]) were applied in the frontal plane. We used frequency-response functions (FRFs) to analyze sway across ~0.045-3Hz and found systematic differences in sway dynamics across segments. Superior segments exhibited larger fluctuations in gain and phase values across frequencies. FRF gains in superior segments were attenuated compared to other segments only at low frequencies but were larger at the higher frequencies. We also tested the influence of stimulus amplitude and visual availability on FRFs. Across all segments, increasing stimulus amplitude and visual availability (EO) resulted in lower gains, however, these effects were most prominent in superior segments. These changes in gain were likely influenced by changes in sensory reliance across test conditions. In conclusion, these results provide a benchmark for future comparisons to segmental responses from individuals with impaired trunk control. We suggest that a frequency-based approach provides detail needed to characterize multi-segment dynamics related to sensorimotor control.

A Trunk Support System to Identify Posture Control Mechanisms in Populations Lacking Independent Sitting

Populations with moderate-to-severe motor control impairments often exhibit degraded trunk control and/or lack the ability to sit unassisted. These populations need more research, yet their underdeveloped trunk control complicates identification of neural mechanisms behind their movements. The purpose of this study was to overcome this barrier by developing the first multi-articulated trunk support system to identify visual, vestibular, and proprioception contributions to posture in populations lacking independent sitting. The system provided external stability at a user-specific level on the trunk, so that body segments above the level of support required active posture control. The system included a tilting surface (controlled via servomotor) as a stimulus to investigate sensory contributions to postural responses. Frequency response and coherence functions between the surface tilt and trunk support were used to characterize system dynamics and indicated that surface tilts were accurately transmitted up to 5 Hz. Feasibility of collecting kinematic data in participants lacking independent sitting was demonstrated in two populations: two typically developing infants, [Formula: see text] months, in a longitudinal study (eight sessions each) and four children with moderate-to-severe cerebral palsy (GMFCS III-V). Adaptability in the system was assessed by testing 16 adults (ages 18-63). Kinematic responses to continuous pseudorandom surface tilts were evaluated across 0.046-2 Hz and qualitative feedback indicated that the trunk support and stimulus were comfortable for all subjects. Concepts underlying the system enable both research for, and rehabilitation in, populations lacking independent sitting.

Effect of Segmental Trunk Support on Posture and Reaching in Children With Cerebral Palsy

PURPOSE

To test the effects of segmental trunk support on seated postural and reaching control in children with cerebral palsy.

METHODS

Seventeen children (age range 2-15 y, Gross Motor Function Classification System levels III-V) were classified with the Segmental Assessment of Trunk Control into mild (complete trunk control/lower lumbar deficits), moderate (thoracic/upper lumbar deficits), and severe (cervical/upper thoracic deficits). Postural and arm kinematics were measured while reaching with trunk support at axillae, mid-ribs, or pelvis.

RESULTS

Children in the mild group did not display changes in posture or reaching across conditions. The moderately involved group showed decrements in postural and reaching performance with pelvic compared with higher supports (P < .01). Children in the severe group were unable to maintain posture with pelvic support and showed postural deficiencies with mid-ribs compared with axillae support (P < .01).

CONCLUSIONS

Children with cerebral palsy and trunk dysfunction demonstrate improved motor performance when the external assistance matches their intrinsic level of trunk control.

The development of trunk control and its relation to reaching in infancy: a longitudinal study

The development of reaching is crucially dependent on the progressive control of the trunk, yet their interrelation has not been addressed in detail. Previous studies on seated reaching evaluated infants during fully supported or unsupported conditions; however, trunk control is progressively developed, starting from the cervical/thoracic followed by the lumbar/pelvic regions for the acquisition of independent sitting. Providing external trunk support at different levels to test the effects of controlling the upper and lower regions of the trunk on reaching provides insight into the mechanisms by which trunk control impacts reaching in infants. Ten healthy infants were recruited at 2.5 months of age and tested longitudinally, until 8 months. During the reaching test, infants were placed in an upright seated position and an adjustable support device provided trunk fixation at pelvic and thoracic levels. Kinematic and electromyographic data were collected. Results showed that prior to independent sitting, postural instability was higher when infants were provided with pelvic compared to thoracic support. Associated reaches were more circuitous, less smooth and less efficient. In response to the instability, there was increased postural muscle activity and arm muscle co-activation. Differences between levels of support were not observed once infants acquired independent sitting. These results suggest that trunk control is acquired in a segmental sequence across the development of upright sitting, and it is tightly correlated with reaching performance.

Segmental Contributions to Trunk Control in Children With Moderate-to-Severe Cerebral Palsy

OBJECTIVE

To examine postural constraints in children with moderate-to-severe cerebral palsy (CP) using a segmental approach.

DESIGN

Quasi-experimental repeated-measures study; case series.

SETTING

Motor control research laboratory.

PARTICIPANTS

Children (N=15; age range, 4-16y) with moderate (Gross Motor Function Classification System [GMFCS] IV; n=8; 4 boys) or severe (GMFCS V) (n=7; 4 boys) CP.

INTERVENTIONS

Each child participated in 3 data collection sessions. During each session, we evaluated postural control for sitting using kinematics and clinical assessments.

MAIN OUTCOME MEASURES

Kinematic data were used to document head alignment and stabilization with external support at 4 levels (axillae, midrib, waist, hip). Two clinical assessments, the Segmental Assessment of Trunk Control and behavioral assessment for stage of trunk control, were also used to compare results for children with CP to previous longitudinal data from typically developing (TD) infants (3-9mo of age).

RESULTS

Children with GMFCS V had difficulty aligning and stabilizing their head along the medial-lateral and anterior-posterior axes. External support improved postural control for children with GMFCS V but not for those classified as GMFCS IV, who had opposite responses to support compared with TD infants.

CONCLUSIONS

Children with GMFCS V have limited trunk control but respond to support similarly to young TD infants, suggesting delayed postural control. Response to external support for children with GMFCS IV suggests a unique strategy for trunk control not observed in typical infants. Overall a segmental approach offers new insights into development of trunk control in children with moderate-to-severe CP.

A model to investigate the mechanisms underlying the emergence and development of independent sitting

When infants first begin to sit independently, they are highly unstable and unable to maintain upright sitting posture for more than a few seconds. Over the course of 3 months, the sitting ability of infants drastically improves. To investigate the mechanisms controlling the development of sitting posture, a single-degree-of-freedom inverted pendulum model was developed. Passive muscle properties were modeled with a stiffness and damping term, while active neurological control was modeled with a time-delayed proportional-integral-derivative (PID) controller. The findings of the simulations suggest that infants primarily utilize passive muscle stiffness to remain upright when they first begin to sit. This passive control mechanism allows the infant to remain upright so that active feedback control mechanisms can develop. The emergence of active control mechanisms allows infants to integrate sensory information into their movements so that they can exhibit more adaptive sitting.

Sitting infants alter the magnitude and structure of postural sway when performing a manual goal-directed task

In typical daily life, adults routinely adapt posture so that balance can be maintained while other goal-directed activities are performed. Interestingly, newly standing infants also control posture based on the demands of a task. It is unknown if the ability to properly adapt postural movements as a goal-directed task is performed emerges soon after the acquisition of independent stance or if it is present at earlier key postural milestones, such as independent sitting. In this study, the postural sway patterns of independently sitting infants were compared while either holding or not holding a toy. Infants exhibited less postural sway when holding the toy. This reduction in sway allowed infants to look at and stabilize the toy in their hand. Thus, the ability to adjust postural movements while performing a concurrent goal-directed task emerges long before the acquisition of independent stance.

Segmental trunk control acquisition and reaching in typically developing infants

This study explored the influence of an external support at the thoracic and pelvic level of the trunk on the success of reaching, postural stability and reaching kinematics while infants reached for a toy. Seventeen infants (4-6 months) were clustered into two groups according to their trunk control assessed with the Segmental Assessment of Trunk Control. Major differences were seen between groups with pelvic support, whereas with thoracic support, all infants showed similar quality reaching behaviors. With the external pelvic support, infants who had acquired trunk control in the lumbar region were more accurate in their reaching movements (less movement time, improved straightness of reach, less movement units and increased path length per movement unit) and were more stable (decreased trunk and head displacement) during a reach than infants who had only acquired trunk control in the thoracic region. These results support the hypothesis that trunk control influences the quality of reaching behavior.