| Children with Attention-Deficit/Hyperactivity Disorder (ADHD) often demonstrate a wide range of behavioral, psychiatric, and cognitive difficulties, particularly in the domain of executive functioning. ADHD is also frequently associated with increased difficulties in motor control, dexterity, and sequencing. Although there have been past reports of motor differences between subtypes of ADHD, only one known study has examined such differences using current diagnostic standards for identifying ADHD-Combined Type (ADHD-C) and ADHD-Predominantly Inattentive Type (ADHD-I). The current study examined the differential pattern of motor deficits between subtypes of ADHD and investigated the relationship between motor deficits and problems in attention, hyperactivity, behavioral inhibition, and executive functioning. Eighty-one children were studied who were between 5 and 12 years of age and were diagnosed with either ADHD-C (n = 49), ADHD-I (n = 30), or ADHD-Predominantly Hyperactive/Impulsive Type (n = 2). Results showed a significant subtype effect on fine motor measures and parent ratings of gross motor skills, with the ADHD-C group performing more poorly than the ADHD-I group. However, these effects were only observed when the effects of age and subtype by age interaction were factored out. The interaction effect on several measures suggested that the younger ADHD-C group tended to perform worse than the ADHD-I group, but that the trend diminished or reversed as age increased. In addition, reduced motor performance in this study was correlated with problems in attention, vigilance, impulsivity, and working memory, but not with behavioral ratings of hyperactivity or disinhibition. These findings provide partial support for Russell Barkley's model of ADHD (1997a,b,c), which proposes that the behavioral, executive, and motor symptoms of ADHD are primarily produced by a central disorder of inhibition. |
