Structure, associated with a motorcycle boot, which is designed to restrict, in the event of accidental falls followed by contact at high speed with the ground, the movements of the leg-piece (12) of the boot with respect to the axis of a heel-piece (14). First hinging means (16) which are angularly movable in a substantially unlimited manner and axially movable between two stopping means and second hinging means (18) which are movable only angularly in a restricted manner. Alternatively, the first and second hinging means can be formed by elements (176, 178) made of elastomeric materials.