Biomechanical analysis of human fall responses.

The epidemic occurrence of falls and fall-related injuries in the elderly is widely recognized, but little specific knowledge of why this happens exists. Whatever the underlying neurological or musculoskeletal causes, responses to an impending fall are ultimately expressed in the body segment motions that ensue and in the joint muscle strengths developed during those responses. Despite this, few studies of fall response biomechanics in either young or elderly subjects have been reported. Healthy young and elderly subjects were accelerated up to.17g while standing on a movable platform. Body segment kinematics, foot/platform reaction, and myoelectric signal data were gathered. An inverse dynamics model of whole body was developed and used for the computation of joint torques and total angular momentum about the whole body pivot point. This model was validated by comparison of computed foot/platform with measured foot/platform reactions. A dynamic optimization scheme was developed to predict the response without recourse to experimental observations. The magnitudes of body segment rotations and joint torques were small compared to maximum range of motions and maximum voluntary strengths. No statistically significant differences between young and old subjects were found in body segment rotations or joint torque magnitudes. Angular momentum about the whole body pivot point was suggested as a measure of the state of balance. Also, timing of angular momentum peaks was used as a parameter of how fast balance was recovered. Although none of the subjects presented any evidence of mobility impairments, significant differences between young and elderly subjects were found in the time required to regain balance. The old subjects stepped in response to the platform acceleration significantly more often than did the young subjects. In the dynamic optimization, sum of the square of second derivative of total angular momentum about the whole body pivot point was used as the objective function. The results predicted by the optimization scheme were in general in good agreement with the experiment results. Also, the optimization result showed that foot/platform reaction was the most important of all the motion constraints.PhDApplied MechanicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/103317/1/9034402.pdfDescription of 9034402.pdf : Restricted to UM users only