Fall Inducing Movable Platform (FIMP) for Overground Trips and Slips
Abstract Background: The study of falls and fall prevention/intervention devices requires the recording of true fallsincidence. However, true falls are rare, random, and difficult to collect in real world settings. A system capableof producing falls in an ecologically valid manner will be very helpful in collecting the data necessary toadvance our understanding of the neuro and musculoskeletal mechanisms underpinning real-world falls events.Methods: A fall inducing movable platform (FIMP) was designed to arrest or accelerate a subject's ankle toinduce a trip or slip. The ankle was arrested posteriorly with an electromagnetic brake and acceleratedanteriorly with a motor. A power spring was connected in series between the ankle and the brake/motor toallow freedom of movement (system transparency) when a fall is not being induced. A gait phase detectionalgorithm was also created to enable precise activation of the fall inducing mechanisms. Statistical ParametricMapping (SPM1D) and one-way repeated measure ANOVA were used to evaluate the ability of the FIMP toinduce a trip or slip.Results: During FIMP induced trips, the brake activates at the terminal swing or mid swing gait phase toinduce the lowering or skipping strategies, respectively. For the lowering strategy, the characteristic leg loweringand subsequent contralateral leg swing was seen in all subjects. Likewise, for the skipping strategy, all subjectsskipped forward on the perturbed leg.Slip was induced by FIMP by using a motor to impart unwanted forward acceleration to the ankle with thehelp of friction-reducing ground sliding sheets. Joint stiffening was observed during the slips, and subjectsuniversally adopted the surfing strategy after the initial slip.Conclusion: The results indicate that FIMP can induce ecologically valid falls under controlled laboratoryconditions. The use of SPM1D in conjunction with FIMP allows for the time varying statistical quanticationof trip and slip reactive kinematics events. With future research, fall recovery anomalies in subjects can nowalso be systematically evaluated through the assessment of other neuromuscular variables such as joint forces,muscle activation and muscle forces.