Center of Pressure (COP) is a clinical measure to investigate the effect of sensory input disturbances on postural stability in the healthy, elderly population as well in people suffering from neuromuscular disease. Increased center of pressure velocity and sway area are interpreted as decreased stability or poor balance and are associated with fall risk. Body mounted inertial sensors have shown great promise as an easily implemented clinical measure of balance. The aim of the present study is to investigate if force-plate and accelerometer measurements provide similar physiological information when approximate entropy (ApEn) are evaluated from a time series. Seven young and thirteen older individuals (two with fall history and nine without any past fall) participated in this study. There were different complexity measures in healthy young and elderly participants when both force-plate and Inertial Measurement Unit (IMU) were assessed during the same time interval. Thus different control mechanisms are underlying to control trunk sway as measured by IMU than that of COP measured by force-plate.