Symmetry of ground reaction forces and muscle activity in asymptomatic subjects during walking, sit-to-stand, and stand-to-sit tasks.

In addition to walking, essential activities of daily living include the ability to rise from a seated position and sit from a standing position. Although many high-quality studies have been performed on these common functional tasks, the objective of the current research is to quantify symmetry indices (SI) of ground reaction force (GRF) and electromyographical (EMG) variables between the non-dominant (ND) and dominant (D) sides of the body in asymptomatic subjects during walking, sit-to-stand, and stand-to-sit tasks. Thirty-five healthy subjects consented to participate in the study that included collection of bilateral GRF and muscle activity of the back, trunk, and legs during the stance phase of walking and sit-stand tasks. No significant differences in SI values between the ND and D sides of the body were found, indicating that asymptomatic subjects walk, stand up, and sit down in a rather symmetric manner. Gait stance time, peak vertical GRF at heel strike, and peak vertical GRF during the entire sit-stand cycle were found to be "perfectly symmetrical" with SI values equal to 1. Future studies will involve similar analyses to determine the level of asymmetry among symptomatic subjects.