The young child's EMG firing pattern is most "primitive" in the plantar flexors, whose activity is radically prolonged in many studies of children. Plantar flexor activity is important to the ankle strategy, and to knee stability in stance. Therefore, poor ankle control leads to generally shorter single limb stance time and generally impaired balance.
Sutherland and others have hypothesized that lack of myelination and slowness of both motor impulses and sensory feedback is responsible for prolongation of muscle activity in children. They point out that CNS myelination occurs in the following sequence:
They further emphasize that this process is complete at about twelve months, the time when most children begin to walk independently.