Longitudinal Development of Manual Motor Performance in Autism Spectrum Disorder from Childhood to Mid-Adulthood and Predictions of Adaptive Daily Living Skills

Background: Cross-sectional studies suggest that individuals with Autism Spectrum Disorder (ASD) exhibit difficulties with motor skills (for a meta-analysis see Fournier et al., 2010). However, the longitudinal development of motor skills in ASD, especially from childhood into adulthood, is unclear. A key question is whether motor skills improve, plateau, or decline in ASD from childhood into adulthood. Because many activities of daily living require manual motor skills (i.e., dressing, preparing food, etc.), another key question is whether difficulty with motor skills is predictive of both current and future adaptive daily living skills.

Objectives: 1) To examine age-related changes in repeated measures of grip strength and finger tapping in ASD compared to typical development from early childhood into mid-adulthood, and 2) to examine manual motor performance as a predictor of current and later (adulthood) daily living skills.

Methods: Ninety males with ASD and 56 age-matched males with typical development between the ages of 5 and 39 years (M = 18.0 years) were included in these analyses. Participants completed bimanual measures of grip strength and finger tapping speed and the Vineland Adaptive Behavior Scales up to three times over the course of 10 years as part of a broader longitudinal study. Mixed-effects penalized regression spline models examined manual motor performance as a function of diagnostic group and age. Partial correlations (controlling for age and IQ) examined whether Time 1 manual motor performance could significantly predict Vineland daily living standard scores concurrently and ten years later.   

Results: The ASD and typically developing groups demonstrated significantly different developmental trajectories for grip strength (p < .001) and finger tapping speed (p < .001). Follow-up analyses demonstrated that in participants younger than 15 years of age, there were trends but no significant group differences in grip strength, t(88) = 1.76, p = .09, d = 0.388, or finger tapping, t(88) = 0.87, p = .39, d = 0.191. However, in individuals 15 years and older, group differences were sizable and significant in both grip strength, t(139) = 6.56, p < .001, d = 1.136, and finger tapping, t(139) = 5.38, p < .001, d = 0.933. Across both groups, grip strength and finger tapping speed significantly predicted both concurrent daily living skills and daily livings skills 10 years into the future (all p’s < .04, controlling for age and IQ). This finding remained even when only including adults in the analyses.

Conclusions: The group with ASD demonstrated atypical manual motor development, characterized by similar performance on grip strength and finger tapping from 5 to 14 years of age but increasingly poorer performance in grip strength and finger tapping from 15 to 39 years of age. These results suggest that individuals with ASD may experience increasingly more pronounced manual motor performance difficulties as they transition from adolescence into adulthood. Moreover, motor skills were found to relate to both current and future daily living skills (both across our entire sample and only in the adults), which suggests that manual motor performance may predict independent living skills in adulthood.