Target your deepest ab muscles with The Boat: Lie face up on a mat with arms by your sides. Lift your upper body off the ground by rolling through the spine and reaching arms forward. At the same time, raise your legs so that you're balancing on your butt, knees bent and shins parallel to the ground. Slowly roll back down onto the mat, lowering legs and arms. That’s 1 rep. Do 5 reps per set, resting 30 to 60 seconds between sets.
“First and foremost you have to train your abs on all three planes. You have to train them forward and back with something like a crunch or double crunch. You have to train your abs laterally to hit the obliques with something like a dumbbell side bend. And you have to train your abs on a rotational plane—your transverse abs—and you can do that from a seated trunk twist."
Plank: Start on your hands and knees and come up into a push-up plank position, balancing on hands (or elbows) and toes (or knees). Align wrists under shoulders; keep your back straight and the abs and glutes tight (to keep the back from sagging). Hold the position and breathe out for 10 seconds, exhaling to tighten the abs and draw the navel to the spine.