Development of speed of repetitive movements in children is determined by structural changes in corticospinal efferents.

This study was aimed to determine the relationship between the maturation of corticospinal efferents, determined by transcranial stimulation of motor cortex, and the development of fastest repetitive voluntary motor activity in children. The development of fastest repetitive voluntary motor activity was assessed for 3 different types of movements including fastest repetitive tapping movements, aiming movements and a pegboard transportation task. These 3 motor activities were chosen as they were different as to their dependence on detailed sensory guidance. Despite these differences the speed of all 3 movements showed a very similar developmental profile, which was matched, however, by the developmental slope of the fastest cortico-motoneuronal efferents. Hence the development of central conduction times determines the speed of repetitive movements in children. In contrast, we could not observe significant effects of repetitive training on speed of these movements. We show for the first time that the development of fastest voluntary movements is a structure-bound phenomenon, being independent from learning.