Abstract: A portable resilient action exercise platform 10 permits the user to jog in place when indoors and provides an increasing resistance to deformation as the amount of deformation of the platform increases. A support assembly including a spaced array of flexible user selectable and replaceable resilient supporting blocks 12 provides a variable amount of support for the exercise platform so that the rebounding action of exercise platform 10 can be varied. Platform 10 preferably includes a spaced array of flexible user-replaceable resilient supporting blocks 12 to absorb the impact of the user's footfalls or movements, and is preferably constructed of strong, flexible structural polymer supported, preferably, by eight or nine resilient flexible user-replaceable foam supporting blocks 12, each preferably comprising a closed cell foam support of selected durometer.