Mechanical effect of additional supports in a rocking on heels movement.

This study examined the influence of the addition of handles on postural adjustments associated to a rocking on heels movement. Upper and lower limb muscle EMG activities were recorded and the forces applied to the handles and beneath the feet were measured. Without handles, the anticipatory activation of the Gastrocnemius Medialis displaced the COP forwards, enabling the backward shift of the CG required to rock back on heels. This anticipatory postural activity disappeared with handles and was substituted by an EMG activity on the upper limbs. This activity engendered a forward and downward push on the handles, which largely contributed to create the dynamic conditions required to perform the movement.