The BOSU cross-body crunch is a dynamic abdominal exercise performed on a BOSU ball or other stability training device. It targets several of the muscles in the core, including the obliques and the rectus abdominis or "six-pack" muscles. It is usually performed in alternating reps, either for time or a number of reps, as part of an ab-focused workout or a circuit involving body weight or the BOSU ball.
More difficult than bodyweight bicycle crunches
Stability challenge from the ball forces the abs to work harder to stabilize
Draping back over the ball between reps can increase the stretch on the abs