The relation between kinematic synergy to stabilize the center of mass during walking and future fall risks: a 1-year longitudinal study

Abstract

Background: Incorrect body weight shifting is a frequent cause of falls, and the control of the whole-body center of mass (CoM) by segmental coordination is essential during walking. Uncontrolled manifold (UCM) analysis is a method of examining the relation between variance in segmental coordination and CoM stability. However, no prospective cohort study has thoroughly investigated how variance in segmental configurations to stabilize the CoM relates to future falls. This study explored whether variance to stabilize the CoM was related to future falls.

Methods: At the baseline visit, 30 community-dwelling older adults walked 20 times on a 6-m walkway. Using kinematic data collected during walking by a three-dimensional motion capture system, UCM analysis was performed to investigate how segmental configuration contributes to CoM stability in the frontal plane. One year after the baseline visit, we evaluated whether the subjects experienced falls. Twelve subjects had experienced falls, and 16 had not. Comparisons of variance between older adults with and without falls were conducted by covariate analysis.

Results: No significant differences in variance were found in the mediolateral direction, whereas in the vertical direction, older adults with fall experiences had a greater variance, reflecting an unstable CoM, than those with no fall experiences.

Conclusions: We verified that the high variance in segmental configurations that destabilize the CoM in the vertical direction was related to future falls. The variables of UCM analysis can be useful for evaluating fall risk.

Keywords: Aging; Center of mass; Falls; Segmental coordination; Uncontrolled manifold.

Fig. 1

Illustrations of the segmental angles for the geometric model. Eight segments and 16 degrees of freedom are used for the analysis; 8 degrees of freedom in the frontal plane (Θ₁: left shank, Θ₂: left thigh, Θ₃: pelvis, Θ₄: right thigh, Θ₅: right shank, Θ₆: lower trunk, Θ₇: upper trunk, Θ₈: head) and 8 degrees of freedom in sagittal and transverse plane (α₁: left shank, α₂: left thigh, α₃: pelvis, α₄: right thigh, α₅: right shank, α₆: lower trunk, α₇: upper trunk, α₈: head). The segments were defined from marker data (black circle) as follows: shank; ankle to knee joint, thigh; knee to hip joint, pelvis; left hip to right hip joint, lower trunk; middle point of both hip joints to T10, upper trunk; T10 to C7, neck; C7 to middle point of foreheads

Fig. 2

Box plots of the CoM position (a, b) and CoM variability (c, d). Box plots of CoM indices in Faller (grey boxes) and Nonfaller (white boxes) for three phases, Early-, Mid-, and Late-SS phases are shown. Dots represent values in each subject. The horizontal line displays the median and the box-edges display the 25th and 75th percentiles. Upper panels: CoM position in the ML (a) and in V (b) directions; Lower panels: CoM variability in the ML (c) and V (d) directions. V direction: vertical direction, ML direction: mediolateral direction, SS: single stance phase. Statistically significant major effects are shown with one star (p < 0.05)

Fig. 3

Box plots of the variance components. Box plots of CoM indices in Faller (grey boxes) and Nonfaller (white boxes) for three phases, Early-, Mid-, and Late-SS phases are shown. Dots represent values in each subject. The horizontal line displays the median and the box-edges display the 25th and 75th percentiles. Upper panels: V_UCM in the ML (a) and V (b) directions, Middle panels: V_ORT in the ML (c) and V (d) directions, Lower panels: ΔV_Z in the ML (e) and V (f) directions. Statistically significant major effects are shown with one star (p < 0.05). For abbreviation, see the caption for Fig. 2

Fig. 4

The correlations between V_ORT for the vertical CoM position and V_UCM for the vertical swing foot position. The horizontal axes represent V_UCM for swing foot position, and the vertical axes represent V_ORT for CoM position. Upper panels: the correlations in the Early-SS phase, Middle panels: the correlations in the Mid-SS phase, Lower panels: the correlations in the Late-SS phase. Statistically, significant correlations are shown with one star (p < 0.05). For abbreviation, see the caption for Fig. 2