A two-stroke internal combustion engine comprises a first cylinder and a second cylinder arranged on a common axis. A method of manufacturing a semiconductor device includes: a formation step of forming a sacrificial layer which is pseudomorphic to InP on an InP substrate, and then forming an InP-based device layer on the sacrificial layer; and a separation step of separating the InP substrate and the device layer from each other by etching the sacrificial layer. Vibration therapy is designed for convenience, portability, therapeutic purposes, and use with other training equipment via a strap attachment. To fill the voids of the elastomeric layers and provide a smooth, flat playing surface, one or more fill layers of dry fill material, such as silica sand, may be formed over the elastomeric layers.