Some ab exercises can strain your spine even if you don't feel pain when you do them.

According to Stuart McGill, PhD, who develop this workout, author of Ultimate Back Fitness and Performance and a professor of spine biomechanics at the University of Waterloo in Canada.

"Perform the moves in the order listed. Hold each for 10 seconds, bracing your abs (as though a ball were going to hit you in the stomach), but don't hold your breath. Repeat 4 to 8 times. Try the Main Move first. If it's too difficult, do the Make It Easier option. When you can complete 8 reps of the Main Move with ease, progress to the Make It Harder version. Do this 15-minute routine once a day, at least an hour after you wake up, so your muscles are warm."  [ see photos above]

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Lie with right knee bent, foot flat on floor, left leg extended, hands under lower back. Lift elbows and inhale deeply. As you exhale, contract abs and curl head, neck, and shoulders to raise shoulder blades a few inches off the floor. Hold and lower, including elbows. Do all reps, then switch legs.

Lie on left side, propped up on elbow, with top foot in front of bottom so both feet are on floor. Contract abs as you raise body, forming a straight line from toes to shoulders. Do all reps, then switch sides.

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Stand with right leg extended behind you, toes on floor. Hold arms out to sides at shoulder height. With abs contracted, bend left knee about 45 degrees, hinging forward a bit from hips, and slide right leg back as arms press forward, palms facing in. (Keep left knee behind toes.) Lift right leg slightly (1 to 2 inches, as pictured) and hold. Straighten left leg to stand, returning right leg to start and pressing arms back out to sides. Do all reps, then switch legs.

Stand with right leg extended behind you so foot is off floor. Raise arms to shoulder height like wings, palms down. Contract abs and hinge torso forward about 45 degrees as you raise right leg behind you as high as possible, while maintaining balance and keeping hips level. Hold, then lower leg to stand and repeat. Do all reps, then switch legs.

watch video on 10min abs workout.