Fig 1.
The trip and slip perturbation system used for this study.
A slip was induced by a movable tile on two hidden low-friction rails with linear bearings that could be unlocked to slide up to 70cm upon foot contact. A trip was induced using a 14cm height tripping board that could be triggered to spring up from the walkway. The tripping board and slipping tile were not visually detectable and could be moved to any location along the walkway. Black and white vinyl stepping tiles were placed on the walkway to reproduce individual’s step length and a metronome was set to the individual’s cadence.
Table 1.
The study protocol.
Fig 2.
Gait parameters during non-perturbed trials (N1 to N6, n = 10) interspersed within slip and trip trials throughout the protocol.
The dots and error bars are means and standard errors, respectively. * p < 0.05, ** p < 0.01, n.s. p > 0.05.
Fig 3.
Changes in pre- and post-slip step kinematics during slip trials (n = 10).
Margin of stability (MoS) was the distance between an extrapolated (i.e. velocity-corrected) centre of mass (XCoM) to the closest base of support limit at foot touch down. XcoM displacement was the distance between the XCoM to the ankle joint of the supporting limb in the sagittal plane. The dots and error bars are means and standard errors, respectively. The arrows indicate the possible directions relating to better stability. S: slip. * p < 0.05, ** p < 0.01, *** p < 0.001, n.s. p > 0.05.
Fig 4.
Changes in pre- and post-trip step kinematics during trip trials (n = 10).
Margin of stability (MoS) was the distance between an extrapolated (i.e. velocity-corrected) centre of mass (XCoM) to the closest base of support limit at foot touch down. XcoM displacement was the distance between the XCoM to the ankle joint of the supporting limb in the sagittal plane. The dots and error bars are means and standard errors, respectively. The arrows indicate the possible directions relating to better stability. T: trip. * p < 0.05, ** p < 0.01, *** p < 0.001, n.s. p > 0.05.
Fig 5.
Strategies for balance recovery after slips (A) and trips (B) (n = 10). S: slip, T: trip. Changes in proportions of balance recovery strategies used were examined by applying the generalized linear mixed model (multinomial or binomial logistic regression). A significant effect of trials was observed in the trip trials (p<0.01). This indicate that the proportions of the lowering strategy in response to trips decreased (T1: 90% to T12: 10%) and the elevating-contact (T1: 0% to T12: 50%) and elevating-cross (T1: 10% to T12: 40%) strategies increased. There was no significant effect of trials in the proportion of strategies during the slip trials.