Many researchers have referred to the human body as an inverted pendulum. The inverted pendulum model, relating the center of mass (COM), the controlled variable, with the center of pressure (COP), the controlling variable, shows that the differences between COP and COM are proportional to the horizontal accelerations of the body. Using the three-dimensional motion analysis synchronized with three force plates, the inverted pendulum model was applied to four different movements (quiet standing, intended postural sway, falling and walking) in twenty healthy volunteers who have no musculoskeletal problems and balance disorders in order to investigate the relationship among COP, COM and the horizontal acceleration of the body. We also performed the crosscorrelation analysis between (COP-COM) and the horizontal acceleration of the body. Results revealed that (COP-COM) had high negative correlations with the horizontal acceleration in quiet standing and postural sway. In addition, high negative correlations between (COP-COM) and horizontal accelerations of the body were found before falling occurs, but high positive correlations were found once falling occurs. However, during walking, high negative correlations between (COPCOM) and midial/lateral accelerations of the body were found. Therefore, the correlation between (COP-COM) and horizontal accelerations of the body based on the inverted pendulum model can be used to determine the postural stability in falling.