The stock market indexes in research on human balance.

PURPOSE: The aim of the study was to demonstrate the possibility of using stock exchange indices to assess the ability to maintain balance as a supplement to analyzes using values determined in the time and frequency domains. METHODS: 83 healthy people (56 females, 27 males, age years 21 SD = 1.3 years) participated in the research. Measurements were performed with open and closed eyes and in the virtual environment with two sceneries oscillating at four frequencies. The results determined in the time and frequency domains were analyzed in relation to the results calculated with the use of stock exchange indicators for which the Trend Change Index was formulated. Performed measurements made it possible to determine the average COP speed, the average COP speed and range of movement towards AP, power spectral density PSD and stock exchange indices. RESULTS: In the case of PSD values for the ranges above and below 0.5 Hz, statistically significant differences occurred for most measurements. Obtained values of TCI coefficient were similar and no statistically significant differences were observed. The maximum values of the PSD medians were obtained in trials with the oscillating scenery. CONCLUSIONS: Conducted analyzes showed that use of stock exchange indicators broadens the interpretative possibilities of COP measurements by determining the number of consecutive skips (changes in the direction) of the COP and prioritizing according to the times between them. The applied stock market analysis methods also filtered out changes in the position resulting from noises that could not be removed with the use of standard low-pass filters.

Analysis of center of pressure displacements and head movements triggered by a visual stimulus created using the virtual reality technology.

PURPOSE: The purpose of the study was to determine how a stimulus presented in the virtual reality environment as a simulation of a fall off the stairs, triggers a loss of balance. The study also examined if the head movement measurements and the analysis in the frequency domain could increase the range of interpretation. METHODS: 11 healthy individuals were tested, two [A1] were identified as more susceptible to the introduced disturbance, and one reported having dizziness, car sickness and fear of heights. Measurements of center of pressure (COP) and head positions were performed in the real and in the virtual environment. The beginning of the simulation was either unexpected or preceded by a signal. The analysis included standard parameters determined in time domain as well as the amplitude of the first harmonic from the fast Fourier transform (FFT). RESULTS: The analysis did not reveal statistically significant differences between results obtained: in real and virtual environments, with and without the warning signal. It was possible to notice the effect of virtual disturbance in the three selected individuals; this was particularly evident in the analysis of the first harmonic of the FFT. CONCLUSIONS: The conducted tests revealed that the limitation of the analyses exclusively to the time domain could be insufficient for a comprehensive interpretation. The effect of introduced disturbance was particularly noticeable in the analysis of the first harmonic for head movement. The application of this parameter could enable a more accurate investigation of a strategy aimed at maintaining balance.

The effect of selected lower limb muscle activities on a level of imbalance in reaction on anterior-posterior ground perturbation.

PURPOSE: We investigated whether an increase in muscular tone induced by the information about imminent posture destabilisation brings a positive result and prevents such destabilisation. METHODS: We measured forward and backwards movements of 38 participates (27 females and 11 males, aged 23 (SD 2.6)) on the treadmill (forward and backward movements). All participants were subjected to three test condition trials (Tr): 1) subject did not know the nature and time of perturbation (Tr1); 2) subject knew the nature of perturbation but did not know time (Tr2); 3) both the time and nature of perturbation were known precisely (Tr3). The tests resulted in the determination of muscular activity connected with a postural adjustment as well as values of pressure exerted by the forefoot on the ground, and the angle of flexion in the knee joint. RESULTS: In terms of postural adjustments, it was possible to observe statistically significant differences in muscular activity between Tr1 and Tr2 with reference to Tr3. No statistically significant differences were identified in all phases regarding values of forefoot pressure and those concerning the angle of flexion in the knee joint. An increase in the muscle tone before perturbation was correlated with the displacement and the velocity of the COP after perturbation. CONCLUSIONS: The results obtained indicate that knowledge of the expected time of perturbation is responsible for postural adjustment. Furthermore, muscle tone resulting from an adjustment of perturbation and responsible for the stiffening of lower limbs triggered greater displacement of the COP after perturbation.