1. An exercise apparatus comprising: a substantially rigid platform; a substantially circular sidewall formed of an inflatable tubular member having an upper and lower surface; said sidewall having a central aperture surrounded by said sidewall; means for engagement of said platform over said central aperture in an engaged position adjacent to said upper surface; said sidewall providing an elevated support for said platform above a support surface, said elevated support having a resilience; said lower surface of said sidewall adapted for placement of said sidewall upon said support surface; said resilience providing both a vertical and horizontal instability to said platform when occupied by a user; and whereby a user stepping onto or exercising upon said platform in an as-used position, will experience a cushioning from said vertical resilience of said tubular member.