Analysis of Stabilograms of Healthy Human Using Time and Frequency Characteristics

Static computer posturography method was used in this work together with stability posture tests to evaluate person's ability to maintain balance. Stabilogram, the curve reflecting the change of person's Center of Pressure (COP) location during balance maintenance, which results in three variables that depend on time - COP point ($\boldsymbol{x}, \boldsymbol{y}$ coordinates) and force applied to that point, was measured during six tasks. For each next task, part of a biological systems that participate in maintaining balance was excluded (visual system first, then proprioception system, then both). COP parameters were obtained in two domains: time (mean and standard deviation of normalized COP coordinates in sagittal and frontal plane, mean and standard deviation of module of normalized COP speed in sagittal and frontal plane, mean and standard deviation of module of normalized COP acceleration in sagittal and frontal plane) and frequency (spectral density power ratio in four frequency ranges: [0; 0.5], [0.5; 1], [1; 1.5], [1.5; 4] Hz for the frontal and sagittal planes). It was found that decrease of posture stability leads to increase of the frequency and amplitude of the COP fluctuations and spectral power is redistributed from low to the higher frequencies. Also, frequency and amplitude of the COP projection in the frontal plane is growing faster than in the sagittal, so instability in the frontal plane is larger due to less contact area of the foot with the supporting surface.