An energy absorber (100) to limit an acceleration force experienced by a heavy body, such as an occupant of a seat subjected to the acceleration of an aircraft crash, comprises a winding drum (10) mounted in rotation around a shaft (13), around which a traction line (11) is wound. The shaft is coupled mechanically to a brake (20) that immobilizes the shaft (13) in rotation when a torque applied to the shaft by the traction line is less than the maximum brake torque that can be generated by the brake and that when the shaft (13) is in rotation generates a torque that is approximately constant and equal to the maximum brake torque.A control element (40) acting on the brake (20) makes it possible to modify the value of the maximum brake torque and thus to adapt the energy absorber to the mass of the heavy body to maintain an acceleration experienced at a desired value for different masses.