The role of anticipatory postural adjustments in a rocking on heels movement

We studied the anticipatory postural adjustments (APAs) associated with a voluntary rocking on heels movement performed in a self-paced manner. Ground reaction forces and the EMG activity of the leg muscles were recorded. Such a movement shifted the centre of gravity (CG) backwards, due to APAs on the lower limbs. It is generally assumed that APAs only generate corrections in the opposite direction to the perturbation due to the focal movement. However, our study shows that APAs, by creating the initial backward oriented impulse, displace the CG backwards and generate the dynamic conditions required to move.