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The development of postural adjustments during reaching in 6- to 18-month-old infants. Evidence for two transitions
I B Van der Fits1, E Otten, A W Klip
1Department of Medical Physiology, University of Groningen, The Netherlands.
Insights
Infant postural adjustments during reaching show two key developmental shifts. Around 8 months, infants gain adaptive postural control, and by 15 months, they develop anticipatory postural activity, especially in neck muscles.
Area of Science:
- Developmental neuroscience
- Motor control
- Human infant development
Background:
- Postural adjustments are crucial for stable reaching movements.
- Understanding infant motor development provides insights into neurological maturation.
- Early motor skills form the foundation for complex actions.
Purpose of the Study:
- To investigate developmental changes in postural adjustments during reaching in infants.
- To identify age-related transitions in motor control strategies.
- To examine the influence of sitting position and movement velocity on infant postural responses.
Main Methods:
- Longitudinal study of 10 healthy infants (6-18 months) and cross-sectional assessment of 18 infants (8-15 months).
- Electromyography (EMG) recorded from arm, neck, trunk, and leg muscles.
- Video recording of reaching movements in upright and long-leg sitting positions.
Main Results:
- Two developmental transitions in postural adjustments were observed.
- Around 6-8 months, infants showed infrequent postural muscle activation, followed by increased and adaptive activity.
- From 15 months, infants demonstrated consistent anticipatory postural adjustments, particularly in neck muscles.
Conclusions:
- Infant postural control during reaching undergoes significant developmental changes.
- Infants develop task-specific adaptation of postural responses by 8 months.
- Anticipatory postural activity emerges around 15 months, indicating advanced motor planning.
Abstract:
The present study focused on the developmental changes of postural adjustments accompanying reaching movements in healthy infants. We made a longitudinal study of ten infants between 6 and 18 months of age. During each session multiple surface electromyograms of arm, neck, trunk and leg muscles at the right side of the body were recorded during right-handed reaching movements in two positions ("upright sitting" in an infant chair and "long-leg" sitting without support). Simultaneously the whole session was recorded on video. Comparable data were present from the same infants at 3-5 months. Additionally, 18 infants (8-15 months) were assessed once during similar reaching tasks, but in these infants electromyographic activity of the trunk and neck muscles at both sides of the body were recorded. Our data revealed two transitions in the development of postural adjustments. The first transition was present around 6 months of age. At this age the postural muscles were infrequently activated during reaching movements. At 8 months ample postural activity reappeared and the infants developed the ability to adapt the postural adjustments to task-specific constraints such as arm movement velocity or the sitting position at the onset of the reaching movement. The second transition occurred between 12 and 15 months. Before 15 months the infants did not show consistent anticipatory postural activity, but from 15 months onwards they did, particularly in the neck muscles.