Leg muscle activation patterns during sit-to-stand on various compliance surfaces

Includes bibliographical references (pages 37-38)BACKGROUND: Previous studies have compared electromyographic (EMG) activity patterns of leg muscles on stable versus unstable supporting surfaces. This research represents a novel approach because the surface stability was modified throughout eight different stiffness conditions ranging from very soft/unstable surface to very firm/hard surface. OBJECTIVE: To analyze EMG activity patterns during sit-to-stand (STS) movement on various compliance surfaces. HYPOTHESIS: The main hypothesis was to look if there were any differences in lower limb muscle activation patterns on various compliance surfaces during sit-to-stand task. A secondary hypothesis was to look if there were any significant bilateral differences in muscle activation between left and right legs on various compliance surfaces. SETTING: Research was conducted at biomechanical lab at California State University, Northridge (CSUN). Supporting surface stiffness was modified with four eight-way adjustable-stiffness shock absorbers mounted between two force plates. A custom built platform was also used in this experiment. PARTICIPANTS: Seventeen CSUN student volunteers were recruited randomly by a pool of volunteers. EXPERIMENTAL PROCEDURE: Each participant performed a self-paced STS under eight surface stiffness conditions in randomized order. MEASURES: The mean EMG values of ten muscles during STS on various compliance surfaces were analyzed and compared according to eight distinct phases of force profile. RESULTS: There were no statistically significant differences found in mean EMG of the muscles examined under different supporting surface stiffness conditions. Right and left leg muscle activities were highly correlated in all phases and not significantly different. DISCUSSION: It was found that muscle activation patterns during sit-to-stand do not significantly change with variations of the surface compliance, suggesting that a sit-to-stand movement skill is preprogramed in a consistent way under all conditions. Regardless of the surface compliance left and right leg muscles were highly synchronized showing strong synergies. This study suggests that there were no neuromuscular adaptations to difference compliance surfaces in STS, but it is suggested to investigate whether long adaptation periods on a softer compliance surface environment will create any different results