Injuries to older adults that are fall-related have become very prevalent in today's society. One third of older adults (65 years and older) report falls each year. This statistic is important to not only the elderly but the younger generations, as well. Health costs and natural aging make this issue important to everyone. Each year between $7-10 billion dollars are spent for health care of injuries that are the result of falls. Eleven percent of elderly falls result in serious injury. Across the country, there are around 250,000 hip fractures a year, most of which occur because impact on the hip region. Over 90% of fractures occur among the elderly, which makes this a rapidly growing health problem. Research has become focused on identifying the factors that are responsible for this high rate of injury. However, little is known about these mechanisms.

The present study examined step recovery among young and old subjects, as well as, male and female. Data was collected for this research in two experimental situations. The experiments were exactly the same in setup and design but differed in the instruction that was given to the subject before the trials began. In the first, the subject was simply told to regain their balance but in the second the subject was told to recover their balance using just a single step. Several step characteristics were measured in order to gain further insight into sources of difference between the groups.

The experimental setup consisted of a horizontal lean control cable, a padded hip belt, a safety harness, force plates, infrared emitting diodes, and an Optotrak. The control cable acted as a pulley to lean the subject out a certain percentage of their body weight. This was attached to the hip belt in order to hold the subject securely. The diodes were placed on the lower extremities of the subject and the Optotrak was used to locate them in three-dimensional space to about .1 mm accuracy. The diodes allowed for the movement of the legs to be tracked at all times. The subjects were leaned out at 15%, 20%, and 25% of their body weight. These trials were presented in sets of three fixed, initially randomized trial blocks where the forward fall was induced after a random time delay by releasing the lean-control cable.

The results were examined for age, gender, and recovery differences. First, differences in age (young vs. old) were examined. Old subjects tended to take a multiple step recovery more often than young subjects, with old female subjects having the largest percentage of multiple step trials. However, when the subjects were instructed to recover their balance with a single step, all groups were able to reduce the percentage of multiple step trials. Therefore indicating that the multiple step trials are not all because of physical limitations. There seems to be some psychological impact and choice. Another difference between the two groups was l iftoff time, the time between the release of the cable and the time a subject lifts their foot from the force plate. Old subjects had a significantly longer liftoff time. Also, lateral movement differed between the ages. Young subjects tended to locate their recovery step closer to the initial midline of their body than old subjects do. At all lean angles tested, the inward lateral movement increased.

Next, gender differences were investigated. The two groups were found to have the exact same step length and step time but significantly different step velocities. This is only possible because the toe clearance, how high the toe is raised above the platform, is larger for males. Therefore, justifying the different step velocities while having a similar step time and step length.

Finally, differences in recovery (single vs. multiple step) were studied. Single step recoveries were found to have a faster step velocity and thus a faster step time. However, liftoff time and step length did not differ between the two groups. Lateral movement was found to differ. The single step recovery was located more toward the midline of the body than the multiple step recovery. This was similar to the age difference in lateral movement. On the multiple step recoveries it was found that the second step usually tended to be lateral to the initial position of the foot in an effort to regain lateral stability.

So it was concluded that elderly prefer to take a multiple step recovery possibly because the first step that is taken to recover their balance does not sufficiently stabilize them laterally. Recovery steps that are located inward were found in young subjects and those who took a single step recovery. This seems to indicate that a smaller mediolateral stance width is more stable than a large one. Young subjects were found to be faster to liftoff and single step recovery had a faster step velocity and step time. Future directions may include studies on lateral movement and center of mass stabilization.