The primary aim of the present study was to investigate if there is an association between symptoms of ADHD and motor skills, in African cultures also, as has already been implicated in Western studies [8,17,24,40,41] and whether these motor problems will differ as a function of ADHD subtype, gender, age, and hand dominance. The study compared South African children from seven different ethnic groups with symptoms of the three ADHD subtypes with a Non-ADHD comparison group on three measures of motor functioning: the Grooved Pegboard, which measures manual dexterity, complex coordination and movement speed; the Maze Coordination Task, which measures complex coordination, goal-directed fine movements, accuracy and stability of movement; and the Finger Tapping Test, which is a simple measure of finger movement and speed [42]. The tasks were performed with both the dominant and the non-dominant hands because when a task is performed with the non-dominant hand, it becomes more complex, probably because it requires continuous attention and more control [43,44].
Association of motor problems with ADHD
The performance of all groups with symptoms of the three ADHD subtypes was significantly poorer on the Grooved Pegboard and the Maze Coordination Task than that of the non-ADHD comparisons. Maybe because the Finger Tapping Test is a simple measure of motor speed and does not involve complex coordination and goal-directed movements, there was no significant difference in performance between the children with ADHD symptomatology and the non-ADHD comparison group on this test. This result replicates that of a European study [45]. Deficits in motor control in ADHD have been reported previously especially when more complex motor sequences have to be performed [43]. Barkley [2] and Leung and Connolly [46] ascribe this to dysfunctional higher-order cognitive processes such as planning and behavioural organising, involved in the more complex motor tasks. However, not all researchers share this opinion. According to Sagvolden and co-workers [15,16] the neurobiological basis is predicted to be a hypofunctioning nigro-striatal dopaminergic system. Neuropsychological studies indicate that the areas involved in ADHD includes the basal ganglia, as well as the cerebellum and the prefrontal cortex [47].
The results of the present study show that the groups with ADHD symptoms were less impaired on the speeded task (Grooved Pegboard) than on the more complex Maze Coordination Task which requires more control, stability, and motor planning. The poor performance on the Maze Coordination Task indicated that children with ADHD symptoms appear to have problems with eye-hand coordination, and control of the task by means of prestructured motor plans [18] as this tasks requires planning ahead. The poorer performance on the Grooved Pegboard especially of the children with symptoms of ADHD-C, suggested that their eye-hand coordination is impaired when motor speed is required [48,49].
Subtypes
All three subgroups showing symptoms of the ADHD had motor performance problems when compared to children without ADHD symptoms. The group with ADHD-C symptoms performed significantly poorer on both the Grooved Pegboard and the Maze Coordination Task, while there were no significant differences for the Finger Tapping Test. It is interesting to notice that the group with ADHD-PI symptoms only differed significantly from the comparison group on the Maze Coordination Task, but not on the Grooved Pegboard. An explanation may be that the Maze Coordination Task is slightly more complex than the Grooved Pegboard, which measures accuracy, and motor speed, but not the same degree of complex eye-hand coordination and motor planning as is required by the Maze Coordination Task.
Only the girls with ADHD-HI symptoms differed significantly from the comparison group in both the Grooved Pegboard and Maze Coordination Task. This was however only the case with the dominant hand. In general, the findings were in line with other studies which found the most pronounced impairment in the children with symptoms of ADHD-C and ADHD-PI subtypes [23,24,41,50-52]. An association between symptoms of inattention and poor motor skills is well-documented [17,23,41]. The study by Pitcher, Piek and Hay [41] found that 58% of children with ADHD-PI, 49% of ADHD-C, and 47% of ADHD-HI were having motor problems. The present study also supports the findings of Hinshaw and co-workers, using the Grooved Pegboard in girls with ADHD, that most impairments are found in the ADHD-C subtype with the ADHD-PI group impaired to a lesser degree [53]. This finding is remarkable as the scores on the Inattention scale of the DBD rating scale did not differ between the two groups (22.86 ± 2.65 vs. 22.84 ± 3.07) and a strong link between inattentiveness and motor dyscontrol has been reported in most studies [22,23,41]. A possible explanation may be that the additional hyperactivity/impulsiveness symptoms add to the impairment of children with symptoms of ADHD-C. The reason may be that poor fine motor skills make greater demands on sustained attention; therefore fine motor movements will be more affected in children with attention deficits than comparison children performing fine motor skills smoothly [41]. There is a strong association between inattention and movement difficulties, as a more pronounced inattention predicts more difficulties in motor coordination [23,41]. The lesser association of ADHD-HI symptoms with motor problems is also confirmed by most studies [41]. Impulsiveness has been associated with motor problems by Tseng and co-workers [54], their explanation was that impulsive children are more inaccurate and do not learn from their mistakes.
Gender differences
Sex differences have only been infrequently assessed in the literature. Gaub and Carlson in their meta-analysis [55] found no difference in motor skills between the genders. In the present study, girls performed both the Grooved Pegboard and the Maze Coordination Task significantly poorer than the boys. This was however only the case with the dominant hand. This finding may support the statement by Biederman and co-workers [56] that, although ADHD is less frequent in girls, the symptoms are more severe than in boys.
Age effect
Age was the most pronounced of the statistical effects. For all measures, except one, significant differences were only found in the younger group with symptoms of ADHD, when compared with the non-ADHD comparison group. The exceptions were the children with ADHD-C symptoms on the Grooved Pegboard. Independent of hand used, their performance was significantly poorer than that of the comparison group without ADHD symptoms. Some studies show that, although some children seem to outgrow their motor problems, they often persist into adulthood [57]. The results could be attributed to the effect of maturation on neuropsychological performance [21] and therefore the tasks could have been insensitive to differences in motor functioning between older children with and without symptoms of ADHD in the present study.
Hand dominance
When the children with symptoms of ADHD showed significantly poorer performance with one hand only, it was the dominant hand. This was the case for both the boys and girls with ADHD-PI symptoms in the Maze Coordination Task and for only the girls with ADHD-HI symptoms on the Grooved Pegboard. This supports the findings of Kalff and co-workers [43] that children at risk for ADHD were disproportionately more inaccurate and had more unstable performance with their preferred hand than other children. The exception was the result of the younger boys with symptoms of ADHD-HI on the Maze Coordination Task where there was a significant poorer performance with the non-dominant hand when compared with their non-ADHD comparisons.
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