An exercise aid comprises an outer casing formed of at least two parts; said parts capable of internally housing a plurality of weighted inserts. The inserts may form a set so that the weight of the aid may be incrementally increased. The inserts may be flat and shaped according to the aid. At least one part of the aid may be moulded to provide a stepped inner, to accept cumulative or contiguous inserts. The inserts may be held in place by a detent mechanism, friction, tolerance fitting or magnetic portions. At least one of the parts may include a semi-spherical outer face. There is also a method of providing abdominal exercise to a post-pregnancy woman according to the claims and figures.