Stabilized exercise device

1. An exercise device comprising:

a convex member having a substantially flat portion, wherein a cavity is accessible from the substantially flat portion through a recess, wherein a lip is formed between the recess and the cavity, wherein the recess has a rounded concave surface configured to butt against a second convex member over an entirety of the rounded concave surface.

2. The exercise device of claim 1 , wherein the convex member of the exercise device has a texture.

3. The exercise device of claim 1 , wherein the substantially flat portion is a predetermined area, wherein the predetermined area is relative to the surface area of the convex member.

4. The exercise device of claim 1 , wherein the lip has a predetermined contour.

5. The exercise device of claim 1 , wherein the lip has a predetermined internal diameter.

6. The exercise device of claim 1 , wherein the cavity is sized relative to an internal diameter of the lip.

7. The exercise device of claim 1 , wherein the cavity has a substantially non-circular ellipsoidal shape when undeformed.

8. An exercise device comprising:

a convex member, wherein a portion of the convex member is substantially flat permitting access to an internal cavity via an opening of the internal cavity, the opening having a recess, wherein the recess has a rounded concave surface configured to butt against a second convex member over an entirety of the rounded concave surface; and

a lip having a predetermined contour formed proximate the opening.

9. The exercise device of claim 8 , wherein the internal cavity has a predetermined shape and volume.

10. The exercise device of claim 8 , wherein the lip has a predetermined internal diameter.

11. The exercise device of claim 8 , wherein the internal cavity is sized relative to an internal diameter of the lip.

12. The exercise device of claim 8 , wherein a protrusion is present around the lip of the internal cavity.

13. An exercise device comprising a convex member with a substantially flat portion, wherein a cavity is disposed on the flat portion and accessible via an opening and the opening has a recess, wherein the recess has a rounded concave surface configured to butt against a second convex member over an entirety of the rounded concave surface to facilitate stacking of the exercise device.

14. The exercise device of claim 13 , wherein the cavity has a plurality of protrusions positioned distal to the lip.

15. The exercise device of claim 13 , wherein an exterior surface of the convex member has a rubberized coating.