Experts once recommended a seemingly endless array of crunches to help sculpt six-pack abs. Today, we know that crunches and situps aren’t likely to get you the ab-fab results you ­really want, and planks reign ­supreme as the ultimate tummy toner. But what makes the ground-gazing move so effective at sculpting your abs? The secret is in the mechanics.

The plank is a static, isometric exercise that requires the abdominals to stop movement while also supporting the spine. It’s a far more functional exercise than crunches, plus planks are generally safer for the lower back. But most important, they work: A 2011 study in Medicine & Science in Sports & Exercise showed that elbow planks were more than twice as effective at core and spine activation than traditional crunches.

The challenge: How can you keep raising the stakes to get flat abs for good? “The plank is a good foundational movement, but you need to progress it if you want a reactive core that helps you move in ways that more closely relate to what happens in real life,” says Josh Henkin, C.S.C.S., creator of Ultimate Sandbag Training. For example, when you pick up your kids, your abs have to react to this unpredictable movement. To keep the demands on your core constantly changing, Henkin has two killer plank variations that will get you sexy abs fast.

Lateral-Drag Plank

  • Begin with the Ultimate Sandbag just outside your right hand. If you don’t have a sandbag, a heavy dumbbell will also do. Grab side of sandbag or dumbbell with your left hand.
  • Keeping your body in a straight line and without rotating your hips, slowly drag the sandbag toward the left side without lifting the weight (aim for a four to six count). Stop when it is completely past your left shoulder and no longer under your torso (shown).
  • Place left hand on floor and drag sandbag with right hand back to start, keeping the same tempo and posture.
  • Repeat, alternating, for 30 seconds.

Super Plank (Elbow to Full)

  • Begin in elbow plank position with your elbows under your shoulders and palms facing each other, feet hip width.
  • Pressing through your toes and keeping tension in your trunk and hips, straighten right arm and plant right hand in top of pushup position.
  • Straighten your left arm, pressing up into pushup position.
  • Hold the plank at the top for one count, then slowly reverse the movement, lowering left forearm and then right, without rotating the hips.
  • Switch the order to lift back up, planting left hand first, then right. Then lower your right elbow first. Continue alternating for 30 seconds.

Want an Ultimate Sandbag (USB)? To get this editor’s pick training tool and for more USB downloadable programs to get toned all over, go to