Abstract: A pair of laterally spaced foot treadles are hinged at their front ends to one end of a hollow base and normally are held in an inclined position by springs. Mounted between each treadle and the base is a normally inflated flexible air chamber that communicates with an air inlet and an air outlet in the base provided with check valves. The outlets of the outlet valves are connected by a conduit that is provided with an exhaust valve, the opening of which is resisted when either treadle is depressed, whereby it requires effort to expel air from the underlying chamber.