An exercise for step aerobics, games, and proprioceptive input training. The device features a rigid platform supported by a resilient inflated tubular sidewall. The sidewall may be of a single tube or a plurality of tubular members engaged on top of each other. Inflation pressure of said sidewall provides an adjustment of the resilience thereby adjusting instability of the platform in the horizontal and vertical directions. Instability in the vertical direction provides a cushioning to users in a step aerobics exercise while instability in both direction provides a manner for a user moving or exercising on the platform to obtain proprioceptive input training.