Gymnastic tool, apparatus and method to carry it out

A unitary gymnastic tool comprising:

• at least two interior chambers, a first chamber defined by a first impermeable external wall, and a second chamber defined by a second impermeable external wall;
• the first and second external walls having facing edges, a planar connecting wall disposed between the facing edges;
• the planar connecting wall fixing the respective edges together so as to make the external walls inseparable, the fixed first impermeable external wall and second external wall forming the unitary gymnastic tool;
• wherein at least the first impermeable exterior wall is in the form of a truncated sphere having a circumferential angle greater than 180° and less than 360°;
• and,
• wherein the planar connecting wall partitions the first chamber from the second chamber, the planar connecting wall having a central hole wherein the two chambers are in fluid communication via the central hole, and wherein the area of the connecting wall is greater than the area of the central hole.