A support device having a receiving surface, a first holding element and a second holding element, the first holding element being movable relative to the receiving surface, the support device including a blocking device having at least one blocking element movable between a release position and at least one blocking position and further including at least one constraint element urging the blocking element towards its release position. The blocking element moves towards its blocking position when the support device is subjected to a blocking acceleration greater than or equal to a predetermined acceleration. The blocking element interacts with a blocking surface in the blocking position.