Factors that influence sitting development
Harbourne RT, Lobo MA, Karst GM, Galloway JC. Sit happens: Does sitting development perturb reaching development, or vice versa? Infant Behav Dev. 2013 Jun;36(3):438-50.
The development of reaching and of sitting during the first year of life is typically studied as separate yet related behaviors. Interestingly, very soon after learning to reach, 4-7-month-old infants start coordinating their arms with their trunk and legs for sitting. In this longitudinal study, we focused, for the first time, on how infants learn to use their arms for the dual tasks of reaching for objects while providing arm support as they learn to sit. We hypothesized that the use of arms for support during sitting development would be a temporary perturbation to reaching and result in a nonlinear progression of reaching skill. Eleven infants were studied monthly from the time they began to prop sit to the time of sitting independence (5-8 months of age). Behavioral coding, kinematics, and electromyography (EMG) characterized reaching and posture while infants sat as independently as possible. Results revealed significant changes across time in trunk movement and hand use as infants transitioned through three stages of sitting: with arm support, sitting briefly without arm support, and sitting independently. Infants used their hands more for contacting objects and less for posture support linearly across time. In contrast, changes in posture control as indicated by pelvis and trunk movement demonstrated a U-shaped curve with more movement of these two body segments during the middle stage of sitting than in the first or last stage. During the middle stage of sitting infants reached persistently even though posture control, measured by pelvis and trunk movement, appeared to be significantly challenged. Muscle activation consisted of tonic and variable combinations of muscle pairings in early sitting. As infants progressed to sitting without hand support, variable but successful strategies utilizing lower extremity muscles in a tight linkage with reach onset emerged to provide prospective control for reaching. Our findings support the contention that reaching both drives the development of sitting in infancy as well as perturbs sitting posture, factoring into the assembly of the complex dual sit-reach behavior that supports and expands flexible interaction with the environment.
Postural control mechanisms
O'Brien KM, Zhang J, Walley PR, Rhoads JF, Haddad JM, Claxton LJ. A model to investigate the mechanisms underlying the emergence and development of independent sitting. Dev Sci. 2015 Jul;18(4):622-34. doi: 10.1111/desc.12238. Epub 2014 Nov 28. PubMed PMID: 25442426.
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.
Deffeyes JE, Harbourne RT, Stuberg WA, Stergiou N. Sensory information utilization and time delays characterize motor developmental pathology in infant sitting postural control. Motor Control. 2011 Apr;15(2):302-17. PubMed PMID: 21628731.
Sitting is one of the first developmental milestones that an infant achieves. Thus measurements of sitting posture present an opportunity to assess sensorimotor development at a young age. Sitting postural sway data were collected using a force plate, and the data were used to train a neural network controller of a model of sitting posture. The trained networks were then probed for sensitivity to position, velocity, and acceleration information at various time delays. Infants with typical development developed a higher reliance on velocity information in control in the anterior-posterior axis, and used more types of information in control in the medial-lateral axis. Infants with delayed development, where the developmental delay was due to cerebral palsy for most of the infants in the study, did not develop this reliance on velocity information, and had less reliance on short latency control mechanisms compared with infants with typical development.
Dusing, S. C., Izzo, T., Thacker, L. R., & Galloway, J. C. (2014). Postural Complexity Influences Development in Infants Born Preterm With Brain Injury: Relating Perception-Action Theory to 3 Cases. Physical Therapy, 94(10), 1508–1516. http://doi.org/10.2522/ptj.20140023
Background and Purpose:Perception-action theory suggests a cyclical relationship between movement and perceptual information. In this case series, changes in postural complexity were used to quantify an infant's action and perception during the development of early motor behaviors.
Case Description:Three infants born preterm with periventricular white matter injury were included.
Outcomes: Longitudinal changes in postural complexity (approximate entropy of the center of pressure), head control, reaching, and global development, measured with the Test of Infant Motor Performance and the Bayley Scales of Infant and Toddler Development, were assessed every 0.5 to 3 months during the first year of life. All 3 infants demonstrated altered postural complexity and developmental delays. However, the timing of the altered postural complexity and the type of delays varied among the infants. For infant 1, reduced postural complexity or limited action while learning to control her head in the midline position may have contributed to her motor delay. However, her ability to adapt her postural complexity eventually may have supported her ability to learn from her environment, as reflected in her relative cognitive strength. For infant 2, limited early postural complexity may have negatively affected his learning through action, resulting in cognitive delay. For infant 3, an increase in postural complexity above typical levels was associated with declining neurological status.
Discussion: Postural complexity is proposed as a measure of perception and action in the postural control system during the development of early behaviors. An optimal, intermediate level of postural complexity supports the use of a variety of postural control strategies and enhances the perception-action cycle. Either excessive or reduced postural complexity may contribute to developmental delays in infants born preterm with white matter injury.
Development of postural stability
Rachwani, J., Santamaria, V., Saavedra, S. L., & Woollacott, M. H. (2015). The development of trunk control and its relation to reaching in infancy: a longitudinal study. Frontiers in Human Neuroscience, 9, 94. http://doi.org/10.3389/fnhum.2015.00094
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.
Saavedra, S. L., van Donkelaar, P., & Woollacott, M. H. (2012). Learning about gravity: segmental assessment of upright control as infants develop independent sitting. Journal of Neurophysiology, 108(8), 2215–2229. http://doi.org/10.1152/jn.01193.2011
The question of how infants attain upright sitting is at the core of understanding the development of most functional abilities. Our simple, practical method of securing the hips and different trunk segments while evaluating the infant's ability to vertically align and stabilize the trunk in space contributes a useful method and new insights into the development of upright control. Previous studies have considered the trunk to develop as a single segment. The goal of the present study was to examine how postural control changes across multiple trunk segments during typical development (TD) of sitting balance. For this purpose, electromyography (EMG) and kinematic data were collected at four levels of trunk support (axillae, midribs, waist, hips), in a longitudinal study of eight TD infants (3–9 mo of age). We found that developmental changes in stability were specific to the region of the trunk being investigated, changes in antagonistic muscle activity differed for the anterior-posterior versus the medial-lateral axis, and the relationship between muscle activation and movement changed from erratic attempts to gain upright position to anticipatory graded responses as infants developed upright control through a four-stage behavioral process. This information can be used by researchers to further refine hypotheses regarding this developmental process and by clinicians who wish to develop and test more specific treatment programs for children with postural dysfunction.
Adaptive sensory motor control
Chen LC, Jeka J, Clark JE. Development of adaptive sensorimotor control in infant sitting posture. Gait Posture. 2016 Mar;45:157-63
A reliable and adaptive relationship between action and perception is necessary for postural control. Our understanding of how this adaptive sensorimotor control develops during infancy is very limited. This study examines the dynamic visual-postural relationship during early development. Twenty healthy infants were divided into 4 developmental groups (each n=5): sitting onset, standing alone, walking onset, and 1-year post-walking. During the experiment, the infant sat independently in a virtual moving-room in which anterior-posterior oscillations of visual motion were presented using a sum-of-sines technique with five input frequencies (from 0.12 to 1.24 Hz). Infants were tested in five conditions that varied in the amplitude of visual motion (from 0 to 8.64 cm). Gain and phase responses of infants' postural sway were analyzed. Our results showed that infants, from a few months post-sitting to 1 year post-walking, were able to control their sitting posture in response to various frequency and amplitude properties of the visual motion. Infants showed an adult-like inverted-U pattern for the frequency response to visual inputs with the highest gain at 0.52 and 0.76 Hz. As the visual motion amplitude increased, the gain response decreased. For the phase response, an adult-like frequency-dependent pattern was observed in all amplitude conditions for the experienced walkers. Newly sitting infants, however, showed variable postural behavior and did not systemically respond to the visual stimulus. Our results suggest that visual-postural entrainment and sensory re-weighting are fundamental processes that are present after a few months post sitting. Sensorimotor refinement during early postural development may result from the interactions of improved self-motion control and enhanced perceptual abilities.
Postural control for reaching
Thelen E1, Spencer JP. Postural control during reaching in young infants: a dynamic systems approach. Neurosci Biobehav Rev. 1998 Jul;22(4):507-14.
We conceptualize the coordinated development of posture and reaching within Schöner's (Ecological Psychology, 7:291-314, 1995) dynamic model of coupled levels of control: load, timing, and goal. In particular, the goal of postural stability must be maintained during a reach. Using longitudinal data from four infants followed from 3 weeks to 1 year, we show that coordination of the head with upper and lower arm activity is critical for successful reaching. First, infants acquire stable head control several weeks before reaching onset. Furthermore, reaching onset is characterized by a reorganization of muscle patterns to include more trapezius and deltoid activity, serving to stabilize the head and shoulder and provide a stable base from which to reach. We argue that initially, the system is working on postural stability and reaching as goals. Infants secondarily select appropriate muscle patterns to achieve those goals depending, in part, on their individual body sizes, body proportions and energy levels. Motor development proceeds as a continual dialogue between the nervous system, body, and environment.
Harbourne, R. T., Lobo, M. A., Karst, G. M., & Cole, J. Infant Behavior and Development Sit happens: Does sitting development perturb reaching development , or vice versa ?
The development of reaching and of sitting during the first year of life is typically studied as separate yet related behaviors. Interestingly, very soon after learning to reach, 4–7- month-old infants start coordinating their arms with their trunk and legs for sitting. In this longitudinal study, we focused, for the first time, on how infants learn to use their arms for the dual tasks of reaching for objects while providing arm support as they learn to sit. We hypothesized that the use of arms for support during sitting development would be a temporary perturbation to reaching and result in a nonlinear progression of reaching skill. Eleven infants were studied monthly from the time they began to prop sit to the time of sitting independence (5–8 months of age). Behavioral coding, kinematics, and electromyo- graphy (EMG) characterized reaching and posture while infants sat as independently as possible. Results revealed significant changes across time in trunk movement and hand use as infants transitioned through three stages of sitting: with arm support, sitting briefly without arm support, and sitting independently. Infants used their hands more for contac- ting objects and less for posture support linearly across time. In contrast, changes in posture control as indicated by pelvis and trunk movement demonstrated a U-shaped curve with more movement of these two body segments during the middle stage of sitting than in the first or last stage. During the middle stage of sitting infants reached persistently even though posture control, measured by pelvis and trunk movement, appeared to be signifi- cantly challenged. Muscle activation consisted of tonic and variable combinations of muscle pairings in early sitting. As infants progressed to sitting without hand support, variable but successful strategies utilizing lower extremity muscles in a tight linkage with reach onset emerged to provide prospective control for reaching. Our findings support the contention that reaching both drives the development of sitting in infancy as well as perturbs sitting posture, factoring into the assembly of the complex dual sit–reach behavior that supports and expands flexible interaction with the environment
Sitting development CP
Boxum AG, van Balen LC, Dijkstra LJ, Hamer EG, Hielkema T, Reinders-Messelink HA, Hadders-Algra M. Postural adjustments in infants at very high risk for cerebral palsy before and after developing the ability to sit independently. Early Hum Dev. 2014 Sep;90(9):435-41. doi: 10.1016/j.earlhumdev.2014.05.011. Epub 2014 Jun 25. PubMed PMID: 24971932.
Children with cerebral palsy (CP) have impaired postural control. Posture is controlled in two levels: direction-specificity, and fine-tuning of direction-specific adjustments, including recruitment order. Literature suggests that direction-specificity might be a prerequisite for independent sitting.
AIM: To study development of postural adjustments in infants at very high risk for CP (VHR-infants) during developing the ability to sit independently.
METHOD: In a longitudinal study surface electromyograms of the neck-, trunk- and arm muscles of 11 VHR-infants and 11 typically developing (TD) infants were recorded during reaching in sitting before and after developing the ability to sit unsupported (median ages: VHR 8.0 and 14.9months; TD 5.7 and 10.4months). Sessions were video-recorded.
RESULTS: In VHR- and TD-infants the prevalence of direction-specific adjustments and recruitment order did not change when the infantlearned to sit independently. In VHR-infants able to sit independently more successful reaching was associated with a higher frequency of bottom-up recruitment (Spearman's rho=0.828, p=0.006) and a lower frequency of simultaneous recruitment (Spearman's rho=-0.701, p=0.035), but not with more direction-specificity. In TD-infants not able to sit independently, more successful reaching was associated with higher rates of direction-specific adjustments at the neck level (Spearman's rho=0.778, p=0.014), but not with recruitment order.
CONCLUSIONS: In VHR- and TD-infants postural adjustments during reaching in terms of direction-specificity and recruitment order are not related to development of independent sitting. Postural adjustments are associated with success of reaching, be it in a different way for VHR- and TD-infants.
Autism and sitting development in infants with ASD
Nickel, L. R., Thatcher, A. R., Keller, F., Wozniak, R. H., & Iverson, J. M. (2013). Posture Development in Infants at Heightened vs. Low Risk for Autism Spectrum Disorders. Infancy : The Official Journal of the International Society on Infant Studies, 18(5), 10.1111/infa.12025. http://doi.org/10.1111/infa.12025
Evidence suggests that children and adults diagnosed with autism spectrum disorders (ASD) exhibit difficulties with postural control. Retrospective video studies of infants later diagnosed with ASD indicate that infants who eventually receive an ASD diagnosis exhibit delays in postural development. This study investigates early posture development prospectively and longitudinally in 22 infants at heightened biological risk for ASD (HR) and 18 infants with no such risk (Low Risk; LR). Four HR infants received an autism diagnosis (AD infants) at 36 months. Infants were videotaped at home at 6, 9, 12, and 14 months during everyday activities and play. All infant postures were coded and classified as to whether or not they were infant-initiated. Relative to LR infants, HR infants were slower to develop skill in sitting and standing postures. AD infants exhibited substantial delays in the emergence of more advanced postures and initiated fewer posture changes. Because posture advances create opportunities for infants to interact with objects and people in new and progressively more sophisticated ways, postural delays may have cascading effects on opportunities for infant exploration and learning. These effects may be greater for infants with ASD, for whom posture delays are more significant.
LeBarton ES, Iverson JM. Associations between gross motor and communicative development in at-risk infants. Infant Behav Dev. 2016 Aug;44:59-67. doi: 10.1016/j.infbeh.2016.05.003. Epub 2016 Jun 14. PubMed PMID: 27314943; PubMed Central PMCID: PMC4992626.
Infants' advances in locomotion relate to advances in communicative development. However, little is known about these relations in infants at risk for delays in these domains and whether they may extend to earlier achievements in gross motor development in infancy. We examined whether advances in sitting and prone locomotion are related to communicative development in infants who have an older sibling with autism spectrum disorder (ASD) and are at risk for motor and communication delays (heightened-risk; HR). We conducted a longitudinal study with 37 HR infants who did not receive an ASD diagnosis at 36 months. Infants were observed monthly between the ages of 5 and 14 months. We assessed gross motor development using the Alberta Infant Motor Scales (AIMS) and recorded ages of onset of verbal and nonverbal communicative behaviors. Results indicated increased presence of early gross motor delay from 5 to 10 months. In addition, there were positive relations between sitting and gesture and babble onset and between prone development and gesture onset. Thus, links between gross motor development and communication extend to at-risk development and provide a starting point for future research on potential cascading consequences of motor advances on communication development.
Assessment of sitting
Butler, P., Saavedra, S., Sofranac, M., Jarvis, S., & Woollacott, M. (2010). Refinement, Reliability and Validity of the Segmental Assessment of Trunk Control (SATCo). Pediatric Physical Therapy : The Official Publication of the Section on Pediatrics of the American Physical Therapy Association, 22(3), 246–257. http://doi.org/10.1097/PEP.0b013e3181e69490 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2927393/#APP1
Purpose: The Segmental Assessment of Trunk Control (SATCo) provides a systematic method of assessing discrete levels of trunk control in children with motor disabilities. This study refined the assessment method and examined reliability and validity of the SATCo.
Methods: After refining guidelines, 102 video recordings of the SATCo were made on 8 infants with typical development followed longitudinally from 3–9 months of age and 24 children with neuromotor disability mean age 10 yr 4 mo. Eight researchers independently scored recordings.
Results:ICC values for inter-rater and intra- reliability were > .84 and >.98 across all data sets and all aspects of control. Tests of concurrent validity with the Alberta Infant Motor Scales resulted in coefficients ranging from .86 to .88.
Conclusion:The SATCo is a reliable and valid measure allowing clinicians greater specificity in assessing trunk control.
Child rearing practices and sitting
Karasik LB, Tamis-LeMonda CS, Adolph KE, Bornstein MH. Places and postures: A cross-cultural comparison of sitting in 5-month-olds. J Cross Cult Psychol. 2015 Sep;46(8):1023-1038. Epub 2015 Jul 13. PubMed PMID: 26924852; PubMed Central https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4767024/
Motor development-traditionally described in terms of age-related stages-is typically studied in the laboratory with participants of Western European descent. Cross-cultural studies typically focus on group differences in age-related stages relative to Western norms. We adopted a less traditional approach: We observed 5-month-olds and their mothers from six cultural groups around the world during one hour at home while they engaged in natural daily activities. We examined group differences in infants' sitting proficiency, everyday opportunities to practice sitting, the surfaces on which sitting took place, and mothers' proximity to sitting infants. Infants had opportunities to practice sitting in varied contexts-including ground, infant chairs, and raised surfaces. Proficiency varied considerably within and between cultural groups: 64% of the sample sat only with support from mother or furniture and 36% sat independently. Some infants sat unsupported for 20+ minutes, in some cases so securely that mothers moved beyond arms' reach of their infants even while infants sat on raised surfaces. Our observations of infant sitting across cultures provide new insights into the striking range of ability, varied opportunities for practice, and contextual factors that influence the proficiency of infant motor skills.