The purpose was to investigate central and peripheral processing mechanisms through the use of electromyography (EMG) to determine differences between the performance of children with and without ADHD on a lower extremity choice response time task. Sixteen children with ADHD were tested on and off medication along with 19 children without ADHD. For premotor time, the comparison group performed significantly faster than children with ADHD. The longer latencies exhibited in central processing of children with ADHD were related to midline crossing inhibition (MCI). Medication improved the speed of processing for children with ADHD, but did not negate MCI.