The bigger the move, the better the ab firming.
AB FACT There’s certainly something to be said for working a muscle through its entire range, but sometimes it’s the tiny contractions that really supercharge your muscles. “Think about a side plank, which is an isometric move,” says Trisha Curling, owner of Ani O Yoga in Toronto. “You don’t see any movement, but you feel it! And you’re working all your deep stabilizers—the multifidus (along the spine), transversus abdominis (360-degree band around your center), and quadratus lumborum (along the back side of the abdominal wall)—plus your rectus abdominis and obliques,” she explains. “In addition, you’re building heat internally, which revs your metabolism.” Another great isometric exercise: Try farmer carries, where you walk back and forth holding a heavy weight in each hand; this lights up the transversus.