Postural control in healthy young adults using a double seesaw device.

Postural control on single and double seesaws was investigated in young healthy adults required to stand as still as possible on two side-by-side seesaws favoring pitch motion and lying on two separate force platforms. The device offers the possibility to get associated or dissociated seesaws and, if dissociated, to induce asymmetric patterns for the centers-of-pressure (CP) under both left and right feet by using different radii for the two seesaws. Substituting a parallelepiped volume to one seesaw offering a firm contact to one foot is also possible. The results indicated that dissociating the two seesaws led to increased resultant CP (CP) and vertically projected center-of-gravity movements (CG) only along the mediolateral axis, whereas a slight decreasing tendency characterized these movements along the antero-posterior axis. When standing on two independent seesaws with different radii, significantly larger CP displacements were seen along the antero-posterior axis under the foot lying on the more stable support, i.e., the seesaw with the longer radius or the parallelepiped volume. In these two asymmetrical conditions, the CP output results from a compensatory mechanism, i.e. larger movements under one foot to compensate for the decreased movements occurring under the opposite foot. This postural control strategy is aimed at allowing sufficient CP displacements in order to appropriately secure balance. Because of the complex sensorimotor coordination induced, involving differentially in certain cases both legs, the double seesaw device can be viewed as a possible tool for challenging postural control by inducing asymmetrical patterns between left and right feet CP movements.