Center of pressure control for balance maintenance during lateral waist-pull perturbations in older adults

Abstract

When balance is disturbed, location of the center of pressure (COP) contributes to a person’s ability to recover from a perturbation. This study investigated COP control prior to first step lift-off (FSLO) during lateral perturbations in older non-fallers and fallers. 38 Non-Fallers and 16 Fallers received lateral waist-pulls at 5 different intensities. Crossover stepping responses at the intensity level where the largest number of subjects responded with crossover steps were analyzed. Whole-body center of mass (COM) and COP positions in the medio-lateral (ML) direction with respect to the base of support (BOS), and COP velocity were calculated. An inverted pendulum model was used to define the BOS stability boundary at FSLO, which was also adjusted using the COP position at FSLO (functional boundary). No significant differences were found in the COP velocities between Fallers and Non-Fallers (p>.093). However, the COP positions for Fallers were located significantly more medial at FSLO (p≤.01), resulting in a significantly reduced functional boundary. Although the stability margins, measures of stability based on the BOS, were significantly larger than zero for Fallers (p≤.004), they were not significantly different from zero for the functional boundary, i.e., reaching the functional stability limit. Fallers had reduced functional limits of stability in the ML direction, which would predispose them to more precarious stability conditions than Non-Fallers. This could be a cause for taking more steps than Non-Fallers for balance recovery as we observed. The functional boundary estimation may be a more sensitive marker of balance instability than the BOS boundary.

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

“…Our previous study found a reduced functional limit of stability for COP movement in older fallers, who took multiple steps more often, compared with older non-fallers, which indicated a functional deficit in stabilizing lateral balance related to a limitation in actively controlling the COP (Fujimoto et al, 2015). In contrast, the COP positions at first step lift-off were similar between the responses in the present study (Table 2), indicating no differences in the functional stability boundaries.…”

“…6 male and 10 female participants had a history of falls during the year prior to testing as indicated by self-report. The exclusion criteria were the same as those reported in our previous studies (Bair et al, 2016; Fujimoto et al, 2015; Young et al, 2013; Yungher et al, 2012). All participants provided written, informed consent prior to participation, and the study was approved by the Institutional Review Board at the University of Maryland School of Medicine and the Baltimore Veteran’s Administration Medical Center.…”

“…The system has been previously described (Pidcoe and Rogers, 1998) and used in prior studies (Bair et al, 2016; Fujimoto et al, 2015; Hilliard et al, 2008; Mille et al, 2013, 2005; Young et al, 2013; Yungher et al, 2012). Six trials were conducted for each of 5 different pull intensities to the left and to the right (2 directions × 5 intensities × 6 repetitions).…”

“…1). Since previous studies have shown that the area functionally used for COP movement is smaller than the actual BOS (Fujimoto et al, 2015, 2013; King et al, 1994), the lateral stability boundary was adjusted based on the COP position at FSLO, considering it as a functional limit for COP movement to control the COM (Fig. 1).…”

Lateral Perturbation-Induced Stepping: Strategies and Predictors in Persons Poststroke

“…The impaired cutaneous sensation of the feet may result in detection errors of the center of pressure beneath the feet in relation to the position and motion of body’s COM and the stability margin of the BOS. 43 In our study, a lateral step of the paretic leg was initiated with comparatively mild deficits in paretic foot cutaneous sensation, and a crossover or medial step was used when the cutaneous sensation of the paretic foot was impaired. The reverse was true when pulled towards the non-paretic side.…”