A glute ham developer comprising a pad assembly and a foot retention assembly. The pad assembly includes a retention sub-assembly coupling a base pad portion to an existing box. The foot retention assembly including a base plate having a foot surface and a support surface. A mating channel extends from the support surface of the base plate. The mating channel is releasably coupled to an existing outside support spaced apart from the existing box. A roller assembly extends from the foot surface of the base plate. The roller assembly has a pair of roller axles in a spaced apart orientation relative to each other defining a foot receiving region therebetween.