Bjo ¨ rn Sondell* Lars Nyberg Staffan Eriksson Department of Community Medicine and Rehabilitation Umeå University Umeå, Sweden *Correspondence to bjorn.sondell@germed.umu.se Bjo ¨ rn Engstro ¨m Anders Backman Kenneth Holmlund VRlab Umeå University Umeå, Sweden Go ¨ sta Bucht Lillemor Lundin-Olsson Department of Community Medicine and Rehabilitation Umeå University Umeå, Sweden Presence, Vol. 14, No. 2, April 2005, 191–197 © 2005 by the Massachusetts Institute of Technology Altered Walking Pattern in a Virtual Environment Abstract Falls and fractures among elderly persons constitute a major health problem. Many falls occur while walking and falls that occur during turning often result in a fracture. Methods aimed at understanding the complex mechanisms involved in walking should therefore assess tested individuals during walks and turns. In order to iden- tify persons at risk and take the correct preventive measures, it is important to find methods that quantify movements as the tested persons are processing multisen- sory input. In a clinical setting this is sometimes difficult to achieve in a controlled manner, since tests are difficult to set exactly the same from one time to another. Using a virtual environment (VE) and a tracker system, conditions such as light, sound, events, body movements, and room size can be controlled and measured. Tests in VE can therefore be identically reproduced over and over again to evaluate if a person can withstand changing outer demands at any given moment. In order to perform quantitative measures 8 persons (21–74 years) were tested in immer- sive virtual reality. The VE was a corridor in which expected and unexpected events could be produced. Events studied were doors swinging open in front of the sub- jects during a walk and a virtual tilting of the environment. Trackers were used for collecting and analyzing the movement data. Our results show that the system was well tolerated among the subjects and that there was a clear tendency that the system could generate fall tendency among the subjects. There was also a differ- ence among the subjects regarding walking strategies when subjected to the various events. 1 Introduction Falls and fall-related injuries pose a serious threat to common health and are the most common cause of injury in old age (Sjo ¨gren & Bjo ¨rnstig, 1989; Nyberg, 1996; Binder, 2002). One in three community-living persons aged 65+ fall every year, many of them more than once, and almost half of these falls lead to an injury. Most falls occur during walking (Jensen, Lundin-Olsson, Nyberg, & Gustafson, 2002). One out of twenty falls leads to a fracture (Ti- netti, Speechley, & Ginter, 1988; Luukinen, Koski, Laippala, & Kivela ¨, 1997). If a fall occurs during turning it more often results in a fracture (Cummings et al., 1995). In Sweden (population 9,000,000), about 18,000 persons suffer a hip fracture every year, and this number will increase as the aging population increases (Socialstyrelsen, 2003). A hip fracture imposes limitations to the af- fected individual and is a common reason for moving to a residential care facil- ity (Sernbo & Johnell, 1993; Tinetti & Williams, 1997). This type of fracture Sondell et al. 191