A base having legs supported on wheels. A second leg may be positioned between first and third legs and the first leg may be positioned between the second leg and a fourth leg. A first gap is positioned between the second and third legs, and a second gap is positioned between the fourth and first legs. The first and second gaps are configured to at least partially receive a user's first and second feet, respectively. A keyway with a bridge may be defined between the first and second legs. A key that may be formed in a fifth leg is removably receivable inside a like keyway of a like base to thereby interlock the bases together so that they are moveable as a unit. An end portion of the key is positionable underneath a like bridge of the like keyway such that the like bridge limits upward movement of the key.
