Changes in the symmetry of external perturbations affect patterns of muscle activity during gait initiation

Gait initiation is associated with changes in the steady state and experiencing an external perturbation during initiation of gait could further threaten balance stability.

The aim of the study was to investigate if changes in the symmetry of the perturbations affect patterns of muscle activity during gait initiation.

Eleven young health participants were instructed to stand on the force platform and wait for the instruction of taking a right step, left step or stand still while experiencing a pendulum perturbation applied to the back of both shoulders (symmetric), back of the right shoulder (asymmetric) or no perturbations. Bilateral electromyographic activity (EMG) of dorsal and ventral muscles, moments of the pendulum release and perturbation impact, center of pressure (COP) displacements and pelvic movements were recorded and analyzed before and after the onset of the perturbation.

Taking the right/left step in presence of symmetric perturbation did not affect the temporal sequence of COP and pelvic movements. The onset of COP and pelvic movement occurred before the perturbation impact at the shoulder levels. The factors of step and perturbation did not significantly affect integrals of bilateral muscles at the pendulum release. After the pendulum release, ventral and dorsal EMG integrals of the trunk, thigh, and shank segments increased or decreased corresponding to the swing and stance leg. Changes in muscle activities were also associated with the symmetric or asymmetric perturbations before and after the perturbation impact.

The outcome of the study provides information about strategies used to coordinate the activity of muscles while body perturbations are induced during gait initiation.