The invention relates to sports apparatuses with unstable surface intended for improving and maintaining ones physical condition. The sports apparatus according to a first embodiment comprises a flexible shell formed as a hermetic chamber with a valve and having an inner space for filling with a filler material and/or air. The hermetic chamber is accommodated within a case with handles. Once the chamber inner space is filled with a filler material and/or air, the sports apparatus in fact forms a rectangular parallelepiped with rounded corners. Side faces of the apparatus form a closed surface. The side face has a height not exceeding a half of the apparatus length. A supporting portion of the apparatus and a portion that the user interacts with are arranged to be identical and outwardly convex. The sports apparatus in operating condition has an elliptical cross-section. Said sports apparatus portions are unstable surfaces.