| The study of gait transitions provides a unique opportunity to study human motor control. Locomotion is a coordination task, a propulsion task, and a postural stability task. At the gait transition, the motor control system must rapidly change patterns of intralimb coordination while maintaining upright postural stability. Additionally, as speed of walking increases, the demand for greater propulsive force increases resulting in increased energy demand. Finally, greater propulsive force and different patterns of coordination will be the result of increases in magnitude and changes in the patterns of muscle activation. This dissertation studies the interaction between these factors and their relationships with the gait transition. The results provide insights into the workings of the motor control system and to the source(s) of sensory feedback within the motor control system that influence the decision to change the type of locomotion pattern.; Two experiments were conducted to examine energy demand, muscular activation, and postural stability at the walk-to-run and run-to-walk transitions. In general, Experiment 1 results indicated that an increase in lower extremity mean muscle activation occurs at the walk-to-run transition, and at the run-to-walk transition, there is a decrease in lower extremity mean muscle activation and a reduction in energy demand. The exceptions to these general findings were energy demand for the walk-to-run transition and muscle activation in tibialis anterior for either transition. The changes for these dependent variables were not significant. Experiment 2 quantified head linear and angular accelerations and head/torso relative phase coordination relationships. Results indicated dependent measures either increased at the walk-to-run transition (head linear acceleration), decreased at the run-to-walk transition (head linear acceleration), or were not significantly different at either transition (head angular acceleration, head vertical/head pitch and head pitch/torso pitch variability of relative phase) at the walk-to-run transition.; Further examination of oxygen consumption, electromyographic activity for tibialis anterior, head angular acceleration, and variability of head vertical/head pitch and head pitch/torso pitch relative phase as predictors of the walk-to-run and run-to-walk transitions using a maintenance (or no significant change) hypothesis is warranted. This information will aid further understanding of the multifactorial nature of the motor control decision-making process. |
