Washington K, Shumway-Cook A, Price R, Ciol M, Kartin D; University of Washington, Seattle, WA., USA. kwpt@u.washington.edu.

PURPOSE: The purpose of this study was to examine the spatial and temporal organization of muscle activity in response to seated forward platform perturbations in infants who were typically developing and in infants at risk for ongoing neuromotor delays. We proposed two hypotheses for the basis of neuromotor delays. First, neuromotor delays in infants at high risk may be due to immature responses to external threats to balance, characterized by a cephalocaudal muscle recruitment pattern. A second hypothesis was that neuromotor delays are associated with abnormalities in the timing and organization of postural muscle activity. SUBJECTS: Twelve infants who were typically developing (TD) and 12 infants with motor delays who were at high risk (HR) for ongoing neuromotor problems participated. All infants were 8 to 10 months of age, and all were independent sitters. METHODS AND MATERIALS: Infants were placed on a moveable balance platform system in long sitting. The system consisted of 2 moveable force plates embedded in the larger stationary balance platform. Ten trials of forward perturbation were given to the seated infants by a horizontal forward translation of the force plates (6 cm amplitude, 12 cm/sec velocity). Surface EMGs recorded muscle responses in the neck, trunk, and leg muscles. Center of pressure (COP) measures including total sway path, root mean square anterior/posterior and medial /lateral displacement, and time to stabilization were recorded. ANALYSES: A non-parametric statistic, the Mann-Whitney U, was used to analyze differences in the types of muscle responses, to compare the spatial organization and temporal characteristics of muscle patterns, and to compare COP measures for the two groups of infants. RESULTS: The infants who were TD demonstrated significantly more (Mann-Whitney U, two-tailed, p = .006) phasic responses than the infants at HR, who had more tonic activity and more no burst trials. The infants who were TD demonstrated caudalcephalo, directionally appropriate recruitment patterns more often than the infants at HR. There were no significant differences between the two groups on any of the COP measures or in onset latencies. CONCLUSIONS: Results suggest that seated postural control in infants at HR for ongoing motor delays can be characterized by elements of both immaturity and abnormality. Increased understanding of the characteristics of postural responses in infants at HR may aid physical therapists in targeting improved intervention strategies for these infants. FUNDING SOURCE: Grant # HD39629, National Center for Medical Rehabilitation Research, National Institute of Child Health and Human Development. No potential material gain for any author.

Copyright 2004 by the American Physical Therapy Association

Reprint Information
Requests for reprints should be directed to the corresponding author of the article. Students and other academic customers may receive permission to reprint copyrighted material from Physical Therapy by contacting the Copyright Clearance Center Inc, 222 Rosewood Dr, Danvers, MA 01923. Similar inquiries by all others should be made to the APTA Editorial Office, Attn: Physical Therapy.