Movement Skill Trajectories Among Children with ASD

Background: Movement skills play a critical role in development.  The performance of movement skills by school-aged children with autism spectrum disorders (ASD) is impaired compared to same aged typically developing peers and to younger typically developing children matched on developmental level.  These movement skill differences become more obvious with increasing age and children with ASD appear to fall further behind -- these increasing differences may reflect the limited opportunities of children with ASD to practice and improve their movement skills.  One theory is that children with ASD do not have requisite skills to build on, which supports the contention of unique developmental trajectories among children with ASD in the movement domain.  However, much of the research to date has examined performance at a single point in time and made inferences about development by looking at studies spanning across age groups.  The use of trajectories puts a focus on change over time within the same individuals.

Objectives: This study explored the performance of 12 fundamental movement skills using the Test of Gross Motor Development (TGMD-2), a standardized assessment that includes specific performance criteria to examine both locomotor and object control skills. 

Methods: 22 children with ASD (aged 9 to 12 years) were individually-matched on movement skill proficiency to 22 typically developing children based on the raw scores from the locomotor and object control subtests of the TGMD-2 (p =  .715 and p = .805,  respectively).  In order to match the groups on movement skill performance, the comparison group was significantly younger (aged 4 to 6 years).  To explore trajectories of movement skill development, 17 children with ASD and 15 typically developing children were followed for 3 consecutive years.  Using hierarchical linear regression, two developmental trajectories were established for each participant, one for locomotor skills and the other for object control skills.  Each trajectory had its own parameters - intercept (i.e., starting point) and gradient (i.e., rate of change). 

Results: The groups were closely matched on movement skill, as such there was no difference in intercepts between the groups on locomotor (p = .983) and object control (p = .538) skills.  However, group differences in the gradients were found on both movement skill subtests (p < .01).  This latter finding supports different developmental trajectories for children with ASD in the movement skill domain.

Conclusions: The significant age difference between these groups clearly demonstrates a delay in the development of movement skills among children with ASD and longitudinal comparisons revealed different developmental trajectories between the groups.  Despite being significantly older, children with ASD seemingly reached a plateau in performance, while the younger, typically developing children continued to refine their movement skills with increasing age.   Intervention approaches need to target these different rates of development.