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How Spreading the Forefeet Apart Influences Upright Standing Control

Patrice R. Rougier

Resultant center-of-pressure (CP) displacements result along mediolateral (ML) and anteroposterior (AP) axes from strategies mobilizing hips and ankles, respectively, and thus, should be largely influenced by the angles between the feet. To assess this relation and the effects of foot position on postural performance, 9 healthy young adults were tested. The main results, as the forefeet are spread farther apart (from 30° in endorotation to 120° in exorotation), indicate (1) a larger contribution of the estimated ankle mechanisms in the generation of the CP trajectories along the ML axis, (2) increased variances along the longitudinal axis of the feet, (3) a constant longitudinal pattern of the CP trajectories under each foot whose main axis displays a progressively increased angle with the inner borders of the feet, and (4) increased variances for CP displacements along both ML and AP axes. These data emphasize the importance of foot positioning in stance control, especially along the ML axis where spreading the forefeet apart progressively increases the contribution of the mechanisms mobilizing the ankles.

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Visual Feedback of Force Platform Displacements for Balance Control Training: What Postural Ability Do Healthy Subjects Have To Develop To Decrease the Difference Between Center of Pressure and Center of Gravity Movements?

Patrice R. Rougier and Samir Boudrahem

Past studies have emphasized the beneficial effect of additional visual feedback (VFB) on the capacity of healthy adults to decrease the amplitudes of the center-of-pressure minus center-of-gravity (CP-CGv) movements. To better assess these capacities, 56 subjects were asked to stand still on a force platform and to use the visual information provided. Dependency coefficients, based on their capacity to lower their CP-CGv movements and therefore relax their lower limb muscles, as well as parameters aimed at characterizing their postural strategies were measured across VFB conditions including (1) CP displacements in real time (VFBCP0), (2) CP displacements with a 600-ms delay (VFBCP600), and (3) CP-CGv displacements with a 600-ms delay (VFBCP-CG600). A non-VFB condition (eyes open) was also included. Several linear correlations were used to specify the relation between subjects’ capacity to relax, compared with the VFBCP0 condition, across the three remaining conditions. The data highlight the complementary nature of the VFB conditions and establish the postural control behaviors necessary to use these VFB protocols efficiently.

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Standing on a Double-Seesaw Device is an Easy Way to Modify the Coordination Between the Two Feet for Controlling Upright Stance: Assessment Through Weight-Bearing Asymmetry

Patrice R. Rougier, Thibaud Coquard, Thierry Paillard, Clément Ankaoua, Jeanne Dury, Corentin Barthod, and Dominic Perennou

Healthy young subjects were instructed to modify their weight-bearing asymmetry when standing on a double-seesaw device. The results indicated decreased and unchanged amplitudes in the center-of-pressure movements under the unloaded and loaded legs, respectively. In addition, a concomitant increased contribution of the more loaded leg and a decreased contribution of the pressure distribution mechanism along the mediolateral axis were observed in the production of the resultant center of pressure, its amplitude remaining constant. Thus, contrary to what was previously reported for stance control on solid ground, one of the main characteristics of a double-seesaw device, by preventing increased amplitudes on the loaded side during weight-bearing asymmetry, would be to facilitate a greater independency of the feet in the stance control process.