Trip recovery strategies following perturbations of variable duration

Abstract

Appropriately responding to mechanical perturbations during gait is critical to maintain balance and avoid falls. Tripping perturbation onset during swing phase is strongly related to the use of different recovery strategies; however, it is insufficient to fully explain how strategies are chosen. The dynamic interactions between the foot and the obstacle may further explain observed recovery strategies but the relationship between such contextual elements and strategy selection has not been explored. In this study, we investigated whether perturbation onset, duration and side could explain strategy selection for all of swing phase. We hypothesized that perturbations of longer duration would elicit lowering and delayed-lowering strategies earlier in swing phase than shorter perturbations. We developed a custom device to trip subjects multiple times while they walked on a treadmill. Seven young, healthy subjects were tripped on the left or right side at 10% to 80% of swing phase for 150 ms, 250 ms or 350 ms. Strategies were characterized by foot motion post-perturbation and identified by an automated algorithm. A multinomial logistic model was used to investigate the effect of perturbation onset, side, and the interaction between duration and onset on recovery strategy selection. Side perturbed did not affect strategy selection. Perturbation duration interacted with onset, limiting the use of elevating strategies to earlier in swing phase with longer perturbations. The choice between delayed-lowering and lowering strategies was not affected by perturbation duration. Although these variables did not fully explain strategy selection, they improved the prediction of strategy used in response to tripping perturbations throughout swing phase.

Effects of exoskeletal gait assistance on the recovery motion following tripping

“…In all the trials, the elevating strategy was selected. This selection was consistent with the relationship between the tripped timing and recovery strategy reported previously [10] A typical recovery motion pattern is shown and described in Fig 3. As one of the features of the elevating strategy, the tripped leg stepped forward at the FS. Furthermore, the recorded reaction motion suggested that the tripping affected the motion of the opposite step, i.e., the SS.…”

“…Regarding the recovery motion following tripping, an elevating strategy was anticipated in this experiment according to previous research studies which analyzed the relationship between the phase of tripping and reaction strategy [8,10]. Furthermore, preliminary experiments suggested that the fall avoidance motion could not be completed within a single step.…”

“…The two major strategies adopted against tripping during gait are the "elevating" and "lowering" strategies [8]. When tripped in the early to the middle parts of the swing phase, humans frequently overcome the obstacle by lifting the tripped leg [9,10]. This is referred to as the elevating strategy.…”

Control strategies for active lower extremity prosthetics and orthotics: a review

“…The user, as an integral element of the control system, is also partially responsible for ensuring safety. This includes the rational avoidance of potentially unsafe situations, but also the response to unexpected locomotive events, such as tripping, stumbling and slipping [ 114 – 116 , 118 , 175 , 199 , 240 ]. Falls represent a substantial hazard to the user, and so the device must (at minimum) not increase the risk of falling.…”

Evidence of impaired neuromuscular responses in the support leg to a destabilizing swing phase perturbation in hemiparetic gait

“…A custom code calculated the average swing phase duration for each subject based on the vertical ground reaction forces output by the treadmill force plates. A custom device (Shirota et al 2014) induced trips by interrupting the foot via a retractable cable attached to the foot (Fig. 1).…”