An inflatable device can be used for physical therapy, conditioning or training. The device has a support platform and a flexible member. The flexible member is affixed to, and has a bowl-shaped distention projecting from, one side of the platform. This flexible member is inflatable to a pressure for supporting a person. The device is inflated before placing at least some of the weight of a person on the device. When the person wishes to later change the characteristics of the device, the pressure in the inflatable device can be changed to change its stability.