Kinematics of recovery from a stumble.

BACKGROUND: Injuries most frequently related to accidents in elderly persons are falls during locomotion and stair ascent and descent. Although numerous risk factors have been related to falling behavior, effective strategies to predict and prevent falls have not evolved. The rationale underlying this study was that systematic experimental and analytical investigation of the effects of perturbations during locomotion and the subsequent requisites for recovery could lead to the development of clinically relevant evaluation(s) capable of identifying a predisposition to falling. The present study is the first biomechanical investigation of recovery from an anteriorly directed stumble. METHODS: Seven healthy, young males participated in this study. While the subjects walked along a walkway in the laboratory, stumbles were unexpectedly induced using a mechanical obstacle. Videotape records of these trials were analyzed and selected sagittal plane kinematics extracted. RESULTS: The perturbation caused an increase in the maximum trunk flexion angle from 4.3 degrees (control) to 18.3 degrees (p = .057), and this change was significantly associated with preperturbation walking velocity (p = .036). The maximum hip and knee flexion angles increased from 26 to 47 degrees (p = .039) and from 60 to 89 degrees (p = .009), respectively. The increases in maximum hip flexion velocity (79%) and maximum knee extension velocity (36%) were not significant. CONCLUSIONS: Identification of the principal elements of control during perturbed locomotion can contribute to understanding the relationship between specific age-related performance deficits and some types of falling behavior. The results suggest that recovery from a stumble is dependent upon lower extremity muscular power and the ability to restore control of the flexing trunk.