How are postural strategies modified along the time?



Postural control is critical for effective performance of all goal-directed activities. For maintenance of postural equilibrium against gravity and environmental disturbances, central nervous system produces centrally organized patterns of muscle activity based on initial conditions, perturbation characteristics, learning and intention. These organized strategies are called "postural strategies". The purpose of this study was to examine how are these strategies modified along the time. For this purpose, eighteen healthy male subjects participated in this study. Subjects were randomly placed (with wide & narrow base of supports) on a tilt board that could be locked in two positions (toe-up & toe-down) at a specified angle. Electromyography (EMG) activity of tibialis anterior, pronea and gastrosoleus muscles was recorded for 10 seconds. The first and last 2 seconds were eliminated to reduce technical error. For every second, integrated electromyography (IEMG) was calculated using special software. Then, data were normalized according to the IEMG of the first second. For all muscles and in all positions, there were significant differences in muscle activity in different times periods (P<0.05). Also, analysis of data revealed a negative correlation between muscle activity and time (0.001