Abstract: An exercise device having two chambers, underlying two elastic membrane portions, in a position to closely support above the ground, the left and right foot respectively, of a user. A support structure such as a housing for the first and second membrane portions permit raising and lowering, as by shifting body weight, of the left and right foot in a stair stepping action, preferably without raising each foot from contact with the membrane portions to elastically stretch the membrane portions in succession. A fluid underlies the first and second elastic membrane portions. The fluid preferably is displaced by the stretching of each membrane portion and in the preferred embodiments, it acts with the membrane portions to support the body of a user in use.