Abstract: A device for aerobic step exercises comprising a platform with a flat top, the underside of the platform having a cavity into which either the first or second end of a support member is inserted. Each end has an opening therein or a slot therethrough of a certain depth which contacts engaging means within the cavity to maintain the top of the platform at a certain pre-selected height above the support surface. A respective numeral corresponding to the height is disposed on the support member adjacent its first and second ends. The numeral can be viewed through an opening in the platform when the support member is inserted into the cavity.