Development of isometric force and force control in children.

Fifty-six children between 5 and 12 years of age and 15 adults performed a task (pressing on a lever with the index finger of the preferred hand), in which a force had to be maintained constant at five levels with on-line visual feedback. Since this is a simple isometric task, the hypothesis is that optimal performance (in terms of force variability control) closely matches the maturation of the corticospinal tract up to age 10. It was found that maximum voluntary contraction (MVC) matured over the full range of the examined age groups. In contrast, the coefficient of variation of force showed maturation mainly up to the age of 9-10, as hypothesised. Gender differences were found for MVC but not for the other force control parameters. Power spectral density analysis revealed developmental differences in the lower (1-6 and 7-12 Hz) and higher frequencies bands (13-18 and 19-24 Hz). In the lowest frequency range the amount of energy decreased with age, presumably because young children (5-8 years of age) rely more heavily on control from proprioceptive and visual feedback. It is argued that with increasing neural maturation the control processes become more dependent upon internal representation manifested by feed forward control that starts to substitute feedback-based control.