A multivariate analysis of frontal plane postural sway: Postural coordination as modified by sensory condition and aging

Documentation of postural sway kinematics presents a challenge to researchers due to the typical non-linear characteristics of biological systems. This research project investigated frequency specific components of frontal plane postural sway to provide quantifiable measures of the coordination between both sides of the body as influenced by altered sensory conditions and aging.;Using a cross-sectional experimental study design, ten healthy young and thirty elderly adults were tested for quality of standing balance using four conditions manipulating visual and surface sensory input. Each subject participated in two test sessions involving the collection of center of pressure (COP) and center of mass (COM) coordinates using two standard force platforms and a 3-D motion analysis system. Bilateral interactions of COP frequencies along with COM dynamic patterns were characterized by a multivariate coherence analysis over a time-varying spectral plane. Variables such as COP signal response magnitude (MAGCOP), phase angle (PHZCOP) and modal frequency (fDOM) were used along with COM root mean square velocity (RMSCOM) and mean squared error (MSE COM) to aid in constructing a statistical model of postural symmetry and coordination. Repeated-measures MANOVA statistics were used to compare coordination indices across age groups and sensory conditions.;Results indicated a significant difference in COP variables relating to phase (PHZCOP) and dominant frequency (f DOM) in healthy elders compared to values for younger participants. Elders in general exhibited at least a 40% increase in phase difference between both sides of the body during quiet stance and a 26% lower dominant frequency. This trend was even greater in elders with higher secondary aging factors. Characteristic equations used to describe sway patterns indicated that vision aided healthy elders in maintaining frequencies similar to that of younger participants. However, decreased somatosensory health or conditions with altered surface feedback, dramatically increased phase differences between both sides of the body in elders with significant associated increases in COM sway variance (MSECOM).;In conclusion, it was found that an analysis of frontal plane postural sway patterns is warranted and that techniques using multivariate spectral analysis, aid in differentiating sensory influenced control mechanisms of standing posture in both the young and elderly.