riding machine
A machine that simulates horseback riding, meant to exercise muscles in the dorsal and abdominal regions.
Although not intended for sexual use, it was suggestively and famously featured in several Idolmaster videos made by Jooba-P.
Not to be confused with a mechanical bull, which is a similar concept, but considerably more vigorous (and would make a poor sex toy on account of its habit of flinging its rider to the floor). Also not be confused with a Sybian, which is for sexual use and only borrows the straddling position of a riding machine.
Examples
