The purpose of this research is to document the development of lower extremity neuromotor control in children. Functional and adaptive motor skills require the task-appropriate combination of muscular and non-muscular forces (e.g., gravity, or the passive-reactive interaction of moving body segments). The muscle force is the only force under neuromotor control. Thus, the acquisition of skill requires that the neuromotor system adjust the muscle response to each context of forces. From the perspective of physics, each force is described by its magnitude and its direction. For successful task completion, then, it is insufficient that we simply produce large quantities of force, we must also apply the force in the appropriate direction. There is no reason to believe that increasing force production capabilities of children (e.g., increases in force magnitude) are automatically accompanied by task-appropriate force direction control. Thus force magnitude and force direction are hypothesized as separable developmental mechanisms contributing to skill acquisition.
We will test this hypothesis by using the task of cycling. Force direction control is necessary to push the pedal around its trajectory and to do this at various speeds. Force magnitude control is necessary to cycle against increasing resistance. Children between the ages of 4 and12 will ride a stationary bicycle, pedaling against at multiple workloads and at multiple cadences. We will monitor both the kinematics of their movements - the positions, velocities, and accelerations of their leg movements - and the muscle activation patterns associated with the pedal trajectories under different workloads and cadences. The central hypothesis is this series of studies is that age is a significant factor only when experience is low. Specific inquries include: A) The effect of maturation: Holding experience constant, we can assess age-related changes in performance and the underlying mechanisms related to muscle coordination and force control. B) The effect of experience: Holding age constant, we can assess the effect of experience on developing force control. C) The adaptability of the neuromotor system: With age- and experienced-matched subjects, we can assess the adaptability of the system by manipulation of cadence and workload in the cycling tasks. These manipulations will reveal age- and experience related trends in responsiveness to changes in context (e.g., external forces). D) Trainability of the neuromotor system: At what age is the neuromotor system responsive to training? By implementing a training study, we can begin to document the effectiveness of training at difference levels of maturation and experience.
The significance of this work lies in its potential contribution to understanding how the developing neuromotor system solves movement problems - specifically the developmental trajectory in the construction of muscular and non-muscular forces to produce functional movement. In the applied domain, this work will also provide information about age-related sensitivity to task manipulations and training. This information is important for understanding children's readiness and responsiveness to educational and therapeutic interventions.
