Abstract The study investigated whether physiological factors related to specific body systems can explain postural control as measured by the scalar distance at a given time between the center of pressure (COP) and the center of mass (COM), the COP–COM variable. The data from 46 healthy subjects and 29 subjects with disabilities due to stroke or diabetic peripheral neuropathy were analyzed. The biomechanical variable COP–COM was determined using two force platforms and an optoelectric system. Three systems were considered as possible predictors of the COP–COM amplitude: sensory (somatosensory and vision), musculoskeletal and central processor. A confirmatory analysis was done using structural equation modeling. Strength explained 23.74% of the COP–COM amplitude in the antero-posterior (A/P) with eyes open (EO) condition, and in the medio-lateral (M/L) direction strength explained 40.73 and 28.75% in the EO and eyes closed (EC) respectively. In the A/P direction with EC, 51.75% of the COP–COM amplitude variance was explained mainly by the somatosensory system. This study highlight the role of peripheral somatosensory input and muscle strength in the maintenance of postural stability during quiet stance in the elderly. The indirect action of the different systems on the COP–COM amplitude supports the systems theory.