Abstract: A relatively rigid molded thermoplastic sheet seat member has a plurality of longitudinally extending ribs forming channel depressions in the seat surface. An annular flange extends from a depending peripheral wall. Three generally cylindrical projections depend from the seat member bottom surface and each including an annular groove for selectively receiving a plurality of elastomeric straps or bands. The bands are formed into two spaced straps and at one end are secured in spaced grooves of a U-shaped grip bar and at the other end pass through an opening in the seat at the seat rear edge and are looped about the projections to set the distance from the seat to the grip. A strap may secure the seat to a chair. A person sits on the seat which overlies the chair seat during exercising the persons arms. Different embodiments are disclosed.