Postural control and adaptation are influenced by preceding postural challenges

We investigated the possible consequences of two consecutive postural tasks on adaptation. Four groups (total number of 46 healthy subjects) were perturbed on two consecutive days with vibration stimulus to tibialis anterior or posterior calf muscles, or both in different orders. Postural movements were recorded with a force platform. There were three major results: (1) tibialis anterior vibration instigated postural adaptation during exposure to the vibration, but did not induce long-term adaptation from day to day, contrary to posterior calf vibration. (2) The long-term postural adaptation from day to day when the posterior calf was vibrated was not affected by prior or subsequent tibialis anterior vibration, which contrasts to other studies on motor learning. (3) Exposure to posterior calf vibration prior tibialis anterior vibration, led to changes of postural strategies and larger amount of torque variance, implying that postural strategies initiated by the gastrocnemius vibration were re-employed during the subsequent tibialis anterior stimulation. This may represent the formation of an internal model, used as feed-forward control of posture, possibly consisting of sensory reweighting. Postural perturbations need to be sufficiently difficult to withstand, in order to induce long-term learning, and postural strategies may be transferred between different postural challenges if they post different demands. Clinically, this suggests that exercises designed to rehabilitate patients should be sufficiently challenging to instigate learning processes, and spaced in order to avoid development of inappropriate postural strategies.