PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 39th ANNUAL MEETING-1995 655 STABILITY LIMITS IN EXTREME POSTURES: EFFECTS OF LOAD POSITIONING AND FOOT PLACEMENT

Although injuries related to postural stability are prevalent, ergonomic job analyses have traditionally not addressed stability issues. In this research, functional stability limits are quantified for persons standing in extreme postures under various external load and foot positioning conditions. Six subjects were tested while standing unladen and while holding a 5.2 kg load. The foot positions, or bases of support (BOS), were varied in width of the stance and sagittal separation of the feet. They were asked to lean and displace their center of gravity (COG) as far as possible in eight directions to the sides and front of the body. Stability measures based on these COG displacements were calculated. All controlled variables significantly affected the stability measures. When standing unladen, subjects extended their COG to within 99 % of their BOS limit. Movement was much more restricted when leaning while handling a load (89%), especially holding it with one hand on the shoulder (84%). On average, increased separation of the feet in a particular direction resulted in larger COG displacements in that direction. The results are discussed relative to their effects on balance and stability modeling