Planks are just about the simplest exercise ever. With correct form, you can work your abs, obliques, shoulders, back, chest, hips, and butt. And you don't even have to move.

"It's not about how long you can hold a plank, but how long you can hold the proper plank," says Rachel Piskin, co-founder of ChaiseFitness in Manhattan and former New York City Ballet.

To get it right, balance on your palms and toes with your body in a straight line between the top of your head and your heels. Your wrists should be underneath your shoulders, with your elbows and knees locked, your hips square to the ground, and your neck neutral. (If you're doing a forearm plank, the same general rules apply. Just place your forearms on the ground and keep your elbows underneath your shoulders.) All you need to do to feel the burn is stay completely still.

Of course, this is easier said than done. Avoid the common mistakes that make planks less effective:

1. You let your hips drop. Droopy hips put pressure on your lower back and rob your core and ass of a good workout. Keep your hips in line with your head and heels to maximize this move's benefits.

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2. You pike your hips. No doubt about it: Sticking your arse up in the air is easier than keeping your body in a straight line. Drop your hips and engage your core and glutes to increase the challenge, and reap the results.

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3. You tilt your hips. Chances are, one side of your body is stronger than the other - and it's normal to collapse into your weaker side. Keep your hips equidistant from the ground to work both sides evenly and keep unnecessary pressure off your lower back.

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4. You drop your head and neck. Tilt your head forward, and you'll disrupt your spinal alignment. Keep your gaze forward and neck relaxed to alleviate tension in your upper back and shoulders, and make it easier to engage your core.

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5. You crane your neck and head up. This puts tremendous pressure on your neck and upper spine, and makes it impossible to maintain proper form, Piskin says.

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6. You round your shoulders. This strains your neck and shoulders. To alleviate the pressure, pull your shoulder blades down your back and open your chest.

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7. You forget about your abs. Planks can work your core just as well as crunches, but only if you mindfully engage your abs. Tighten your stomach muscles to support your spine and turn belly flab into sexy definition.

8. You forget about your butt. Most people don't know that planks work your butt, big time. Squeeze your glute muscles to help keep your hips up and stay in plank position longer.

9. You position your hands too far apart or stagger them. Keeping your wrists and elbows stacked directly underneath your shoulders protects your wrists from pain than can ruin your plank and continue to ache hours later. Make sure the front of your fingers align to work both sides of the body evenly.

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10. You bend your knees. This common mistake gives your butt a break, which reduces the overall effectiveness of the plank position. Straighten your legs and pull your kneecaps up your thighs to support your hips and keep your spine super straight.

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Rachel is wearing Floral Leggings, Without Walls; Zigzag Sports Bra, Without Walls; Coral Sneakers, ADIDAS; with hair by Alexandra Kress and makeup by Denise Del Russo.

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From Cosmopolitan USA.

From: Cosmopolitan US