Transient Changes In Muscle Activations

The instantaneous speed of walking is a function of the kinematics of limbs which in turn are determined by the forces generated in muscles through the application of the laws of motion from Newtonian mechanics. The movement is actively controlled by the motor commands generated in the central nervous system and sent to the musculoskeletal system through the descending tracts. These motor commands can be estimated with the electrical activities in the muscle tissue, which are recorded using electromyography (EMG) techniques. The activity of muscles as a function of time, also known as muscle activations provides information on how the motor commands change in order to control movement of the limbs and achieve a desired goal in this case a certain speed for walking. To study these changes, in this chapter we propose an experiment that elicits transient changes in muscle activations through the application of perturbations in a virtual reality environment.
Hypothesis #1: By averaging muscle activations over all gait cycles for each trial, we cannot differentiate between patterns of muscle activity during transient responses and those observed during steady-state walking trials. We will use a system identification approach to derive muscle activation profiles for perturbed trials and repeat the analysis using steady-state averaging method and then compare the results to normal walking trials to demonstrate the differences. Statistical tests will be used to evaluate the significance of the difference between normal and perturbed walking for the two methods of analysis. We also compare the qualitative patterns of changes in steady-state walking to changes in transient