An exercise device includes a deflatable spherical exercise ball mounted on a frame for rotation above a support surface that supports the frame so that the ball rotates freely without interference from the support surface. The frame is foldable so that when the ball is deflated, the frame may be stored in a space substantially smaller than the space occupied by the exercise device when in a fully deployed configuration. A first pair of inclined tubes is pivotally connected to one another at their respective upper ends so that they collectively form an inverted "V" shape when the device is fully deployed. A second pair of inclined tubes is transversely opposed to the first pair of inclined tubes. A forward base includes foot restraints. The first and second pairs of inclined tubes are coplanar with the forward base when the device is folded.