Is the motor impairment in Attention Deficit Hyperactivity Disorder (ADHD) a co-occurring deficit or a phenotypic characteristic?

Objectives: Motor difficulties are often reported in individuals with attention deficit hyperactivity disorder (ADHD). The aims of this study are to detail the motor profile of children with ADHD and to determine whether the motor impairment present in a large proportion of children with ADHD represents a phenotypic characteristic of ADHD or a co-occurring deficit. Methods: Participants with ADHD (N = 51; age 8 to 15 years) and typically developing (TD) motor matched control children (N = 75; age 4 to 11 years) completed the largest battery of assessments of motor function that have been used with this population to date, as well as a measure of inhibition as a behavioural measure of ADHD characteristics. Parents/caregivers also completed questionnaires relating to ADHD symptomology and a retrospective report of their child’s motor milestone achievement. Results: A motor deficit was observed in 47% of our ADHD sample. Few relationships were observed between ADHD core characteristics and motor competence. Furthermore, there was an uneven profile of motor performance across different motor tasks, relative to the TD children. Interestingly, it appears that motor milestone achievement is not delayed in ADHD. Conclusions: Our findings suggest that the motor deficit observed in ADHD is not inherent to ADHD. The motor deficit observed in some children with ADHD does not represent a simple delay in development and is not observed in infancy with respect to reaching motor milestones.