13 Moves That Trainers Swear Will Strengthen Even the Deepest Part of Your Core

"This move is great because it forces the TVA [your transverse abdominis] to stabilize while you add movement that works the obliques," Allison Tibbs, NASM-certified personal trainer, said. "It's definitely a one-two punch for creating strong and defined abs."

• In a plank, open your knee to the side and bring your left knee to your left elbow and right knee to right elbow, alternate sides.
• Allison says to repeat this for 30 to 60 seconds.