Single and multiple step balance recovery responses can be different at first step lift-off following lateral waist-pull perturbations in older adults

Abstract

An inability to recover lateral balance with a single step is predictive of future falls in older adults. This study investigated if balance stability at first step lift-off (FSLO) would be different between multiple and single stepping responses to lateral perturbations. 54 healthy older adults received left and right waist-pulls at 5 different intensities (levels 1–5). Crossover stepping responses at and above intensity level 3 that induced both single and multiple steps were analyzed. Whole-body center of mass (COM) and center of pressure (COP) positions in the medio-lateral direction with respect to the base of support were calculated. An inverted pendulum model was used to define the lateral stability boundary, which was also adjusted using the COP position at FSLO (functional boundary). No significant differences were detected in the COP positions between the responses at FSLO (p ≥ 0.075), indicating no difference in the functional boundaries between the responses. Significantly smaller stability margins were observed at first step landing for multiple steps at all levels (p ≤ 0.024), while stability margins were also significantly smaller at FSLO for level 3 and 4 (p ≤0.048). These findings indicate that although reduced stability at first foot contact would be associated with taking additional steps, stepping responses could also be attributable to the COM motion state as early as first step lift-off, preceding foot contact. Perturbation-based training interventions aimed at improving the reactive control of stability would reduce initial balance instability at first step lift-off and possibly the consequent need for multiple steps in response to balance perturbations.

Perturbation-evoked lateral steps in older adults: Why take two steps when one will do?

“…Consistent with previous studies following forward loss of balance, a reduced first step MoS was found for multistep responses compared to single step responses (Arampatzis et al, 2008; Barrett et al, 2012; Carty et al, 2011; Carty et al, 2012) and in cross-over steps following a lateral loss of balance (Fujimoto et al, 2017). Additionally, the stability limit was not reached at first step termination in many cases despite additional steps being taken, a finding consistent with previous reports that steps are frequently taken before the stability limit is reached (Pai et al, 1998).…”

“…Differences in MoS between multistep and single step responses, in the present study, were attributable to differences in CoM velocity at step termination and the BoS-CoM relationship. There were no significant differences in BoS boundary as a result of multistep responses compared to single step responses, which is consistent with anteroposterior perturbations (Arampatzis et al, 2008; Carty et al, 2012) and previous work in cross-over steps (Fujimoto et al, 2017). These results indicate efficient CoM control is an important factor in achieving a sufficient MoS to avoid additional protective steps.…”

“…Therefore, the functional BoS would be more accurately defined by the center of pressure location, as reduced functional center of pressure limits have been shown to discriminate between fallers and non-fallers (Fujimoto et al, 2015). However, no difference in the functional base of support in single versus multistep responses was identified in a study of lateral stepping (Fujimoto et al, 2017). Based on results of previous work (Fujimoto et al, 2017), the relative differences in MoS between single and multistep response would likely be similar to those found if functional BoS were reported in this study.…”

“…The CNS appears to alter the response in real time (Fujimoto et al, 2017) based on the evolving balance state, i.e. the central nervous system (CNS) monitors the current and future states of the CoM relative to the BoS (Maki and McIlroy, 1999; Rogers and Mille, 2016).…”

“…the central nervous system (CNS) monitors the current and future states of the CoM relative to the BoS (Maki and McIlroy, 1999; Rogers and Mille, 2016). Reduced dynamic stability at first step foot contact, and as early as first step lift off, has been linked with additional steps following lateral perturbations (Fujimoto et al, 2017), although only cross-over step types were analyzed. Reduced dynamic stability at first step foot contact following an anterior-posterior perturbation (Carty et al, 2011) has also been linked with additional steps.…”