Introduction: Changes that occur during stance on a soft surface also appear at the level of the central nervous system and are similar to changes seen in motor learning. Aim: In this study on young and healthy subjects we were interested in effects of successive stance on a soft surface on the movement of center of pressure and whether they reach a plateau. Methods: The study involved 17 young subjects, 12 females and 5 males. The subjects were aged 18 to 25 years. We examined the effects of standing on a soft surface on center of pressure for ten consecutive days. The subjects were standing on the pressure plate Kistler 9286AA which Airex® pad was placed on (in 3rd and 4th condition), without shoes, with their feet tight together, hands relaxed along the body, the head straightened. For the performed measurements we used the modified sensory interaction test. Measurements: 1. firm surface - eyes opened, 2. firm surface – eyes closed, 3. soft surface – eyes opened, 4. soft surface – eyes closed. The test lasted for 60 seconds. On the first and last day, we carried out all four measurements, while the rest of the days we only performed measurements on a soft pad as balance training. Observed variables were path x, path y, mean velocity of the center of pressure, surface area of movement of the center of pressure using the PCA method and FAO method. Results: T test showed statistically significant difference (p<0.05) only while standing on a soft surface with eyes closed between the first last measurement when moving the center of pressure in the AP and the ML direction and at the velocity of the movement of the center of pressure. When standing on a soft surface with eyes closed, the path of movement of center of pressure in the AP direction decreases by 17%, in the ML direction by 19% and the velocity of movement of center of pressure also decreases by 18%. With eyes closed, the area also decreases by 12%. The analysis of 10 consecutive measurements showed significant difference between the ninth and tenth consecutive measurement (p = 0.011) for the AP path of center of pressure on soft surface with eyes opened. For the other three variables, the differences between the individual measurements were not statistically significant. With eyes closed, the AP path variable approached the limit of statistical significance (p = 0.078). The post hoc test showed the largest difference between the first and tenth measurement (p = 0.101). Discussion and conclusion: The obtained results did not show statistically significant changes between consecutive measurements, therefore, we cannot conclude on the greater stability or the effect of motor learning in repetitive standing on a soft surface. In order to generalize the results we should repeat the study with larger number of subject and/or increase the number of training units and/or increase the complexity of stance.
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