Jansen RD, Nansel DD, Szlazak M, Four Quadrant Forceplate Analysis of Postural Sway: Frequency Domain Characteristics Transactions of the Pacific Consortium for Chiropractic Research: {Proceedings of the Third Annual Conference on Research and Education Jun 18-19, 1988; A3: 1 – 11

Previous investigations of posture sway in humans using power spectral density analysis of center of force, though often judged promising, have consistently yielded high variability across individual trials as well as across subjects. Improvements in power spectral analysis are suggested, and a method of using eight or more 50 second standing trials per experimental condition with statistical tests between blocks is utilized. Test results are also contrasted with a two-week interval between measurements to display statistically consistent differences in spectra induced by eye closure. In addition, direction of sway was investigated by generating frequency distributions of vector angles and magnitude (sampled at 40ms) for each experimental block of eight or more trials. Results suggest that vector magnitudes (velocities) increase significantly with eye closure, while dominant direc