The Reach-Through exercise works your shoulders, abs and obliques.
-The Weekend Slim-Down: Sleeker Saturday. Reach-Through: From side plank position, you're gonna raise your right arm straight up and then reach it through under your belly. Bring your arms straight up again to start the next rep. If it's too touch to do with a dumbbell, just do the move without it. Do 8 to 10 reps, switch sides, and repeat.