The Relationship Between Motor Coordination and Intelligence Across the IQ Range

OBJECTIVE: In both clinical practice and research, motor delay is understood to be explained, at least in part, by intellectual abilities; however, no data are available to operationalize these criteria to guide clinical decision making. This study provides data on IQ and motor skills in children to answer 3 research questions concerning the relationship between IQ and motor skill: (1) Can motor coordination impairment be explained in terms of general intellectual retardation? (2) What level of motor performance should be expected given the person's measured intelligence? (3) At what point are motor difficulties considered to be in excess of those usually associated with mental retardation?

METHODS: IQ and motor skill data were analyzed from a group of 460 children identified with/without motor difficulties from both clinical and educational settings.

RESULTS: Typical and atypical motor skill was seen at all IQ levels, 19% of the variance in motor outcomes was explained by IQ scores, and for each SD lower IQ, a mean loss of 10 percentile motor points should be expected.

CONCLUSIONS: Although individuals with a lower measured IQ more often showed poorer motor performance than those with a higher measured IQ, motor skill at all levels of proficiency was seen in all IQ categories. These findings have important implications for clinical judgments and decision-making, as well as for future research directions to further operationalize the criteria relating to motor disorders in both the Diagnostic and Statistical Manual of Mental Disorders, Fourth Revision, and the International Classification of Diseases, 10th Revision.