Mechanisms Leading to a Fall From an Induced Trip in Healthy Older Adults

Abstract

BACKGROUND: Tripping is a leading cause of falls in older adults, often resulting in serious injury. Although the requirements for recovery from a trip are well characterized, the mechanisms whereby trips by older adults actually result in falls are not known. This study sought to identify such mechanisms. METHODS: Trips were induced during gait in 79 healthy, community-dwelling, safety-harnessed, older adults (50 women) using a concealed, mechanical obstacle. Kinematic and kinetic variables describing the recovery attempts were compared between those who fell and those who recovered. Subjects were analyzed 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 lowering 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 second; 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 lumbar flexion and buckling of the recovery limb. The elevating strategy fall was associated with a faster walking speed (93% vs 68% +/- 11% bh per second; 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, accompanied by back and knee extensor weakness, may also lead to falls following a trip. Deficient stepping responses did not contribute to the falls.