DO YOUNG HEALTHY ATHLETES MAINTAIN BETTER THEIR STANDING EQUILIBRIUM IF BAREFOOTED?

Abstract

INTRODUCTION: The present study assessed the influence of sport shoes on the maintenance of equilibrium while standing on a monoaxis tilting platform. METHODS: Ten young healthy athletes (5 women, 5 men) aged 19-25 years (mean 21.5) were asked to stand on a 65x65 cm wooden platform that tilted on a steel half sphere with a 25 cm radius. The subjects were instructed to keep the platform as horizontal as possible over a 30 s test. The task was repeated three times with the subjects barefooted, and three times with the subjects wearing their own (habitual) sport shoes. To avoid the effect of fatigue, each test was performed with a 30 minutes interval, and to avoid any learning effect, the order of the six tests was randomized between the 10 subjects. A 2-cm spherical retro-reflective marker was positioned on each of the four corners of the platform. During the test, the three-dimensional coordinates of the centers of gravity of the markers were automatically collected using a motion analyzer system (ELITE, BTS, Milan, Italy). The system consists of four high resolution infrared sensitive CCD video cameras coupled with a video processor. The system has a sampling ratio of 100 Hz, and 3000 sets of data were therefore available for each subject and test. For each set of data, original software calculated the movement of the platform versus the ground (reference) in the last 20 s of each test. From the center of gravity of the platform (origin of axes), the directrix of the plane was computed. Its vertical movements appeared negligible, and only its antero-posterior and laterolateral (left-right) inclinations were further analyzed by computing the instantaneous angular velocity during the trial, the area of the confidence ellipse of the directrix at length 1 (proportional to the variability of the oscillation), and the distance between the origin of axes and the center of the ellipse (modulus, which is proportional to the mean oscillation). Bivariate analysis was used for the last two calculations. Mean values were computed for the barefooted and sport shoes conditions, and compared using Student’s t. RESULTS: On average, when barefooted, the subjects showed a significantly smaller area of oscillation (i.e., the platform movement was less variable) than when wearing sport shoes (p<0.05). Consistent (but not significant) modifications were found in the other variables. No gender differences were found. CONCLUSIONS: The proprioceptive receptors of the foot and ankle seem to work faster and more efficiently in barefooted young athletes, allowing a better maintenance of posture, with smaller oscillations in the horizontal plane.