Recovery From a Forward Falling Slip: Measurement of Dynamic Stability and Strength Requirements Using a Split-Belt Instrumented Treadmill

Abstract

Aim: Falls commonly occur from trips and slips while walking. Recovery strategies from trips and backward falling slips have been extensively studied. However, until recently, forward falling slips (FFSs) have been considered less dangerous and have been understudied. This study aimed first to create an application to realistically simulate FFSs using a split-belt instrumented treadmill and then to understand the biomechanical requirements for young adults to recover from an FFS. Methods: We developed a semi-automatic custom-made application on D-Flow that triggered FFSs by briefly and unexpectedly increasing the speed (a = 5 m•s −2) of the right belt during stance. To validate the protocol, we tested against criteria defined for an ecologically and experimentally valid FFS: unexpected occurrence of the slip, increased foot velocity, forward loss of balance during the slip and consistent perturbation timing. We evaluated the recovery strategies of 17 young adults by measuring dynamic stability, joint moments and ground reaction force (GRF) vector angles before, during and on 15 steps following the FFS. Results: The application successfully triggered FFSs, according to the criteria we defined. Participants' balance returned to normal for a minimum of three consecutive steps in 10.9 (7.0) steps. Recovery from the FFSs was characterised by larger hip flexor and knee extensor moments to support the centre of mass during the slip, and a longer first recovery step with large hip extensor moments to arrest the fall followed by large knee extensor moments to raise and advance the centre of mass into the next step (p < 0.001 compared with normal gait). Subsequent steps progressively returned to normal. Conclusion: This is the first study to experimentally simulate FFSs meeting the aforementioned criteria, and to measure their effects on the dynamic balance and kinetic parameters. The split-belt instrumented treadmill proved a promising tool to better study the mechanisms of falls and recovery. The required large hip and knee joint moments generally agree with findings on trips and backward falling slips and provide an indication of the functional capacities that should be targeted in fall-prevention interventions. These findings should be used to better understand and target the mechanisms of balance loss and falls in older adults following FFSs.

Small Directional Treadmill Perturbations Induce Differential Gait Stability Adaptation

“…4), suggesting that subjects were destabilized initially before gradually regaining stability during the Stick0.4, Slip0.4, and M1 perturbations. These results are consistent with previous studies that showed that treadmill belt and shift perturbations decreased MoS AP (Debelle et al 2020; McAndrew Young et al 2012; McCrum et al 2018). Adjusting foot placement and BoS is a common approach to modulate MoS (Hof et al 2010; Süptitz et al 2013), which was evident in our Stick0.4 perturbation.…”

“…Adjusting foot placement and BoS is a common approach to modulate MoS (Hof et al 2010; Süptitz et al 2013), which was evident in our Stick0.4 perturbation. Other studies demonstrated the importance of center of mass control to modulate MoS (Debelle et al 2020; McCrum et al 2019), which was evident in the Slip0.4 and M1 perturbations. MoS did not always decrease in response to perturbations.…”

“…Both the BoS AP and XcoM AP increased in response to our Slip0.4 perturbation, but subjects mainly modulated their XcoM AP while adapting to the Slip0.4 perturbation. The XcoM AP responses were likely related to the decreased hip flexor moment of the right stance leg to reduce the forward rotation and acceleration of the upper body (Debelle et al 2020). Even though the BoS AP also changed during adaptation, these changes were smaller than the XcoM AP and were probably a consequence of the facilitated forward swing phase induced by the Slip0.4 perturbation.…”

“…Perturbations during walking can induce potential losses of balance and elicit corrective locomotor adaptations, which are useful for understanding human balance control (Mansfield et al 2015; Torres-Oviedo et al 2011). There are multiple approaches to perturb gait stability, including split-belt walking (Buurke et al 2018; Torres-Oviedo et al 2011), visual flow distortions (Franz et al 2016; O’Connor and Kuo 2009), waist pulling (Hof et al 2010; Vlutters et al 2018), platform displacements (Afschrift et al 2018; McIntosh et al 2017), and rapid changes in treadmill belt speed (Debelle et al 2020; Patel and Bhatt 2018). Studies using discrete perturbations such as waist pulling, platform displacements, and changes in treadmill belt speeds often apply the perturbation once out of every 5-20 strides (Afschrift et al 2018; Debelle et al 2020; Hof et al 2010; McIntosh et al 2017; Patel and Bhatt 2018; Vlutters et al 2018).…”

Children With Developmental Coordination Disorder Show Altered Visuomotor Control During Stair Negotiation Associated With Heightened State Anxiety

“…where pCoM is the AP position of the CoM, vCoM is the instantaneous AP velocity of the CoM, g is acceleration due to gravity, and l is the absolute distance between the CoM and the ankle joint center. Margin of stability was calculated at initial contact on each of the seven steps (Debelle et al, 2020). For ascent, foot-step-edge clearance was defined as the minimum vertical distance between toe markers on the lead limb and the step edges (toe clearance).…”