Mechanisms leading to a fall from an induced trip in healthy older adults

Background. Tripping is a leading cause of falls in older adults. often res ulting in serious injury. Although the requirements for recovery from a tri p are well characterized, the mechanisms whereby trips by older adults actu ally result in falls are not known. This study sought to identify such mech anisms. Methods. Trips were induced during gait in 79 healthy, community-dwelling, safety-harnessed, older adults (50 women) using a concealed. mechanical obs tacle. Kinematic and kinetic variables describing the recovery attempts wer e compared between those who fell and those who recovered. Subjects were an alyzed according to the recovery strategy employed (lowering vs elevating) and the time of the "fall" (during step vs after step). Results. Three apparent mechanisms of falling were identified. For a loweri ng strategy, during-step falls were associated with a faster walking speed at the time of the trip (91% +/- 8% vs 68% +/- 11% body height [bh] per sec ond; p < .001) and delayed support limb loading (267 +/- 49 milliseconds vs 160 +/- 39 milliseconds; p < .001). After-step falls were associated with a more anterior head-arms-torso center of mass at the time of the trip (6.2 +/- 1.3 degrees vs 0.2 +/- 4.4 degrees; p < .01), followed by excessive lu mbar flexion and buckling of the recovery limb. The elevating strategy fall was associated with a faster walking speed (93% vs 68% +/- 11% bh per seco nd: p < .001) followed by excessive lumbar flexion. Conclusions. Walking quickly may be the greatest cause of falling following a trip in healthy older adults. An anterior body mass carriage, accompanie d by back and knee extensor weakness, may also lead to falls following a tr ip. Deficient stepping responses did not contribute to the falls.