title: Mechanisms of Balance Recovery from a Slip and Interventions in Older Adults
Creators: name: Debelle, H
Publisher: name: Liverpool John Moores University
Year: 2023

description: Falls in older adults can have major health and economic consequences. Slips with forward loss of balance have long been considered less dangerous than other types of gait perturbations and have scarcely been investigated. It has however recently been shown that slips with forward loss of balance can trigger falls that can lead to severe injuries for older adults. At present, the mechanisms by which older adults recover their balance following slips with forward loss of balance are unknown, which hinders our capability to design effective evidence-based fall prevention interventions. Therefore, this thesis aims to comprehensively investigate the biomechanics of balance recovery following induced slips, and to explore possible fall prevention interventions aiming at improving participants’ balance recovery. First, a slip-like gait perturbation protocol, that reduces participants’ stability and was developed using a split-belt instrumented treadmill, is presented and tested in young adults. Chapter 2 shows that this protocol is experimentally valid, and that young participants recover their balance over multiple steps through an adjustment of their gait kinetics and kinematics. In Chapter 3, the same protocol is applied to older and younger adults using repeated perturbations to assess the mechanisms of balance recovery and the adjustments to repeated perturbations. Both young and older participants could recover their balance and learn how to better recover with repeated exposures. Independent of age group, participants modified their knee moments, ankle moments and step length following the first slip, and most of these changes were correlated with poor balance on the following steps. Improved balance recovery with repeated perturbations was achieved by refining these kinetic and kinematic responses to retain only those beneficial strategies (increased step length). Finally in Chapter 4, balance recovery is correlated with participants muscle-tendon units’ properties, and a nutritional (collagen and vitamin C) intervention aiming at improving older participants’ tendon stiffness is trialled. Following findings from Chapter 2 and 3, muscle-tendon units’ properties which may be relevant for balance recovery were selected for analysis, but despite this specificity no significant relationship was found between the selected properties of the muscle-tendon units and participants’ balance recovery. These findings suggest that fall prevention interventions focussing on the maximum mechanical properties of the effectors would likely not improve participants balance recovery following this type of gait perturbation because recovery may not rely on maximal properties of the effectors. On the contrary, as shown in Chapter 3, interventions training the motor task itself seem to be effective at improving balance recovery within the training session, and could therefore be used as preventive interventions to decrease older adults’ risk of falling if long term retention existed. The Covid-19 pandemic impacted the nutritional intervention to the extent that it is not possible to provide a definitive conclusion concerning potential effects of collagen and vitamin C supplements on tendons’ mechanical properties.