Contributions of Distinct Trunk Segments to Control of Posture and Reaching During Typical Development
Rachwani Parshotam, Jaya
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Rachwani Parshotam, Jaya
The relationship between the development of sitting postural control and of reaching during infancy has not been addressed in detail. It has recently been shown that trunk control develops starting with the head, then the upper trunk and subsequently the lower/pelvic regions. However, previous studies on infant reaching evaluated infants during supported supine or reclined sitting positions, failing to address the contributions of distinct regions of the trunk to reaching. This dissertation explores the relationship between the progression of trunk control and reaching performance in healthy infants. The effects of stabilizing the upper and lower regions of the trunk were assessed by providing vertical trunk fixation at two levels of support (thoracic and pelvic). Documentation of postural and reaching performance reflected how control of the free regions of the trunk modulated both behaviors. First, kinematic data were collected in infants aged 4-6 months who were grouped according to their sitting ability and extent of trunk control. Second, a longitudinal study was implemented in which kinematic and electromyographic recordings were collected bi-monthly from 2.5-8 months. Results from the cross-sectional study showed that postural stability and reaching kinematics of the two groups were similar when they received support at the thoracic level but differed when the support was limited to the pelvic level. Infants who were able to sit independently outperformed the infants who were unable to sit without help. These data were further expanded with the results obtained from the longitudinal study, showing that during the months prior to independent sitting, infant reaches were impoverished and were associated with a lack of postural stability when provided with pelvic, in comparison to thoracic, support. In addition, infants displayed inefficient muscle patterns in response to the instability. Differences between levels of support were not observed once infants acquired independent sitting. Taken together, these results offer detailed measures of the progression of trunk control and its relation to reaching. This raises important questions regarding whether this more specific approach may create the foundation for evaluating and improving trunk control in atypically developing populations. This dissertation includes previously published and unpublished co-authored material.