Abstract: An exercise bicycle is composed of a base frame and an adjunct device. The base frame is formed of a first support tube, a second support tube, and a seat. The first support tube is provided with a shaft tube on which a crank is mounted. The crank is provided with two support shafts separated from each other for fastening pedals. The second support tube is located between two ends of the base frame and is provided at the top end thereof with a handlebar. The adjunct device consists of two long tread rods of a metal material and provided with two foot pads. The long tread rods are fastened pivotally and respectively at one end thereof with the crank such that another ends of said long tread rods are supported by two support elements at a level for doing a reciprocating motion. An exerciser is seated on the seat such that both feet of the exerciser pedal, or that the exerciser stands on the foot pads for doing a revolving treading motion.

Abstract: A foldable bicycle frame comprises a front frame made up of a head tube, a top tube and a down tube, and a rear frame made up of a seat tube, a bottom bracket tube, a seat stay and a chain stay. The top tube is provided at the rear end thereof with a connection tube to receive therein a seat post. The bottom bracket tube is provided at the center of the front end thereof with an extension tube which faces the front wheel and is pivoted at the front end thereof to the bottom end of the down tube. The front frame and the rear frame are fastened together by means of the seat post which is inserted into the connection tube and the seat tube. The front frame and the rear frame are rotatable in relation to each other when the seat post is pulled out of the seat tube.

Abstract: A foldable bicycle frame comprises a front triangular portion and a rear triangular portion. The former includes a top tube, a down tube, a head tube and a seat tube while the latter contains a bottom bracket tube, a seat stay, a chain stay and a seat tube. Both front and rear triangular portions are hinged by means of upper and lower coupling pieces so that they can pivot to be folded. Upon being unfolded, both front and rear triangular portions are held securely by virtue of a seat stay which extends beyond the seat tube to be fastened securely to the top tube. Front and rear triangular portions can be also held so securely in another manner that a seat post is inserted into connection tube and seat tube which are coaxially arranged.