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Updated: Sep 27, 2026
An Instrumented Pull Test to Characterize Postural Responses
Published on: April 6, 2019
Longitudinal Development of the Automatic Postural Response in Infants
H. Sveistrup1, M. H. Woollacott
1Department of Occupational Therapy, Faculty of Health Sciences, University of Ottawa, 451 Smyth, Ottawa, Ontario 1H 8M5, Canada.
Insights
Infants develop automatic postural responses by coordinating muscle activation, progressing from single muscles to functional synergies. This sensory-motor development continues even after independent walking begins.
Area of Science:
- Developmental motor control
- Neuroscience
- Biomechanics
Background:
- Postural control is crucial for independent movement.
- The development of automatic postural responses (APRs) in infants is not fully understood.
- Understanding APR development informs interventions for motor impairments.
Purpose of the Study:
- To investigate the developmental trajectory of automatic postural responses in infants.
- To analyze muscle activation patterns and timing during postural perturbations.
- To determine how sensory-motor organization evolves during early locomotion.
Main Methods:
- Longitudinal study of 9 infants from pre-independent standing to independent walking.
- Surface electromyography (sEMG) recorded leg and trunk muscle activity.
- Analysis of muscle onset latencies and activation consistency following support surface translations.
Main Results:
- Infants initially activated muscles in isolation or pairs, progressing to functional synergies.
- Three-muscle postural responses were inconsistent in younger, non-walking infants.
- The proportion of trials with muscle activity increased significantly (p < .05) post-independent walking.
Conclusions:
- Automatic postural responses develop progressively, starting with simpler muscle activations.
- Functional muscle synergies emerge as infants gain postural control and independent walking skills.
- This study highlights the maturation of sensory-motor organization during infant development.
Abstract:
In this longitudinal study, the development of automatic postural responses elicited during stance following perturbation of the support surface was investigated. Infants (N = 9) unable to stand without support were tested initially: follow-up tests were performed until the infants were able to stand and walk independently. Surface electromyographic recordings of leg and trunk muscle activity following a postural perturbation induced by a forward or backward translation of the support surface were made for each infant. Muscle onset latencies following the perturbation and the proportion of trials in which muscle activity was recorded were determined. First, infants activated appropriate muscles either in isolation or in pairs and then combined these muscles into functional synergies. Although activation of all three postural muscles was recorded in infants before they were able to stand and walk independently, the three-muscle response was not consistent in the youngest children. The proportion of trials eliciting muscle activity continued to increase (p <.O5) after infants began to walk independently, with postural muscle activity recorded in virtually every trial by late independent walking. Thus. the automatic postural response elicited during stance was shown to begin with activity in single or paired muscles, followed by activation of the postural muscles in functional synergies. These data illustrate the progressive development of an effective sensory-motor organization.
