The Biomechanics of Reactions to Impending Falls (Myoelectric Latencies, Kinematics).

The biomechanics of human responses to impending falls were investigated in a first attempt study through use of experimental observations of subjects and model simulations. Responses of subjects, initially st and ing, to a horizontal floor anterior step acceleration pulse of mean amplitude 0.18g were recorded in terms of whole body sagittal plane motions and myoelectric activities. The 11 normal male subjects exhibited complex responses in arresting the impending fall this stimulus initiated. Four distinct patterns of body segment response motions were observed in the first 500 ms of response: whole body movement, upper body rigid, whole body rigid, and stepping responses. Myoelectric activity measurements showed that the ankle joint muscles contracted first, beginning at about 135 ms after initiation of motion, and muscles crossing each more superior joint were contracted later. Trunk agonist and antagonist muscles were cocontracted for a period of between 100 ms to 400 ms. Nine and 12-body simulation models were used to calculate joint response torques from the body kinematic and myoelectric latency measurements. The joint torques were largest at the ankles and knees (30% to 120% maximum voluntary strength), and smaller at the hips, torso and shoulder joints. These torques resisted dorsiflexion and extension moments in the ankle and knee, while at the hip, torso and arm joints they resisted at various times both flexion and extension moments.PhDBiomedical engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161309/1/8702819.pd