Short-term effects on postural control can be evidenced using a seesaw

▶ When standing on a seesaw, a new coordination needs to be learned again. ▶ This coordination involves both center of pressure (CP) and center of gravity (CG). ▶ The effects of this learning can be highlighted after a 20min training. ▶ Its main effect is a decrease of the difference between CP and CG movements. ▶ This decrease stems from a lessened control of the CP–CG movements. Postural control strategies are frequently assessed through posturography on a firm surface. Their motor efficiency is related to the coordination between center-of-gravity (CG) and center-of-pressure (CP) movements, which results from long-term training. However, when standing on a seesaw favoring pitching body motions, a new coordination, requiring short-term training, needs to be learned again. On this type of device, somesthetic cues from the ankle joints become invalid and motor command is amplified because of the curvature of the contact ridges. To highlight the mechanisms involved in short-term improvements of postural control, 11 healthy young adults were trained for 20min by standing on a seesaw with their eyes closed. Two series of posturographic measurements, before and after the training, were recorded whilst the subjects stood on the seesaw with eyes closed. The results indicate a reduction in the horizontal CG displacements along the anteroposterior axis and CP–CG displacements along both anteroposterior and mediolateral axes. Fractional Brownian motion (fBm) analysis further explains these lessened CG movements by highlighting a reduced distance covered before the corrective mechanisms take over. The other fBm parameters, the contribution of stochastic activity during the shortest and longest time intervals or the time interval of the transition points (which expresses the mean delay before the corrective mechanisms take over), remained unchanged. These results could likely be explained by reduced tonic muscular activity of the lower limbs and/or recalibration of the sensory systems in order to improve the detection of the CG movements.