The present invention relates to a device of the type for building up the upper and lower limbs in particular, which has at least two resistance forces, and preferably three forces. These forces are obtained without adding a supplementary part, and without any particular adjustment. The device has a substantially oval shape (1) and has two lateral extensions (4, 5) of the "ear" type, which, inter alia, allow it to be grasped by a user. This device also comprises two strips (6, 7) which are thinner than those of the other, main strip which forms the assembly of the device (2, 3, 4, 5).