The invention relates to a back module (2) for an exoskeleton structure, comprising a spinal column segment (21) designed to extend along a spinal column of a user, the spinal column segment (21) comprising a plurality of vertebral elements (211), stacked on one another, and a flexible connecting element (212) connecting the vertebral elements (211) to one another, the spinal column segment (21) having a stable equilibrium position in which the flexible connecting element (212) holds the vertebral elements (211) supported against one another, and the flexible connecting element (212) being elastic so that, during a movement of the back of the user, the flexible connecting element (212) allows a movement of the vertebral elements (211) with respect to one another, while exerting a return force tending to return the spinal column segment (21) the stable equilibrium position.