Biomechanics of slips and falls in the elderly: Effects of restricted arm motion on recovery strategies
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Slip and fall accidents pose a serious threat to elderly individuals. Several researchers, over the past few decades, have successfully quantified different gait parameters pertaining to the biomechanics of slips and falls to help reduce the incidence of slip and fall accidents in the elderly. However, a comprehensive understanding of mechanisms including strategies used by the elderly for recovery during a slippery perturbation under different arm restriction conditions is still lacking. This research study investigated gait patterns in young and elderly individuals, in terms of proactive and reactive strategies that individuals used to reduce their likelihood of a fall related injury during a slippery perturbation under different arm restriction conditions. In addition to the gait parameters, the strength capabilities of the lower extremities of young and elderly individuals were also explored. Lastly, a logistic regression equation was developed to predict falls and recoveries. The study did help identify successful strategies used for recovery under different arm restriction conditions. In addition, unsuccessful reactive movements that resulted in falls were also pointed out. Proactive strategies identified including reduced step length, walking velocity, heel contact velocity and foot floor angle were used by both younger and older individuals when they knew the floor was slippery. Reduced step length, foot floor angle and walking velocity were also noted when one or two arms of individuals were restricted. In terms of age, more elderly individuals fell when compared to younger individuals. Several other variables including average sliding heel velocity, peak sliding heel deceleration and separation between whole body center of mass and sliding heel also showed differences for age. Significant differences were noted not only between older and younger individuals but also between fallers and non-fallers in terms of the recovery effort. Variables including average sliding heel velocity, maximum and minimum differences between the upper body center of mass (UBCOM) and the lower body center of mass (LBCOM) showed differences between fallers and non-fallers. In terms of arm restriction, both young and older individuals showed significant differences in maximum wrist velocities for the different arm restriction conditions. Differences in maximum velocities between the WBCOM and heel when comparing the no-arm and two-arm restriction, and also the no-arm and one-arm conditions were also found. In terms of strength, knee and ankle torques were found to be significantly higher for younger individuals when compared to elderly individuals. The leg collapse that was observed which resulted in falls was an additional indicator of poor strength in the elderly. The primary contribution to elderly gait literature and the biomechanics of slips and falls through this study was the development of a novel method through the exploration of UBCOM-LBCOM dynamics during recovery effort from a slippery perturbation under different arm restriction conditions. In terms of findings, the study did show that individuals were able to recover better when their arms were not restricted. The study did also show that the elder fallers were unable to ‘catch up’ by moving their trunk (and UBCOM) quickly to keep up with the sliding heel (and the LBCOM. On the other hand, younger non-fallers were able to have a higher difference in velocities between the UBCOM and LBCOM, and still ‘catch up’ successfully. Thus, the study of UBCOM-LBCOM dynamics might be useful in better understanding elderly slips and falls.