1. An exercise apparatus comprising: a substantially rigid platform; a substantially circular sidewall formed of an inflatable first tubular member stacked upon an inflatable second tubular member situated upon a support surface, said sidewall having an upper surface and a lower surface; means for engagement of a bottom surface area of said first tubular member to a top surface area of said second tubular member; said sidewall having a central aperture defined by said sidewall; means for engagement of said platform over said central aperture in an engaged position adjacent to said upper surface of said sidewall; said sidewall providing an elevated support for said platform above said 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; said first tubular member inflatable to a first pressure level and said second tubular member independently inflatable to a second pressure level wherein one of said first pressure level and said second pressure level can be varied to adjust said resilience and thereby vary said vertical and horizontal instability.