Exercise machine with moveable user support

User support assembly (12, 12A, 202) pivotable in two directions for supporting a user during an exercise movement on an exercise machine, comprising: a base (28, 224); a user support connected to the base (28, 224), the user support being rotatable about a first axis (19, 225) during an exercise; and a locking mechanism (14) disposed between the base (28, 224) and the user support, where a locking device (14, 204) of the locking mechanism (14) has: (i) a first locked position defining a stable support mode in which the user support rotates only about the first pivot axis (19, 225) and is locked against rotation about a second pivot axis (20 , 275), and (ii) a second release position defining an unstable support mode in which the user support is free to rotate about said second pivot axis (20, 275) where in the release position the support platform (15, 223) is configured to freely pivot up and down between zero and five degrees on each side about the second pivot axis (20, 275), where the second axis, (20, 275) extends parallel to the plane of the support platform (15, 275) in a front to rear direction, and said platform is tilted or swung back and forth about said second axis (20, 275).