1. The problem: You crunch too high.
These are crunches, not sit-ups. When you crunch high, you take the emphasis off of your rectus abdominis and onto your hip flexors, says Brett Hoebel, creator of the 20 Minute Body and celebrity trainer on The Biggest Loser season 11.
The fix: Focus on bringing your ribs down to your belly button, he says. It will raise your chest a few inches off of the ground. That little motion is all you need to target your abs.
2. The problem: You use momentum.
"If you rush through your reps, you aren't going to get the same benefits you would if you slowed down," says Brennan. "You end up using momentum rather than strength, so you take your abs completely out of the equation." Even worse, it can put extra force on your joints and up your risk of back injury.
The fix: Keep your movements slow and controlled. At the end of each rep, pause with your back firmly against the floor. Reset before moving on to the next rep, she says.
3. The problem: You yank your neck.
"You don't want your hands and arms helping you do the crunch," Hoebel says. And you probably don't want to strain your neck, either.
The fix: Work on maintaining an apple-size space between your chin and chest throughout the entire movement, Brennan says. If you still find yourself yanking on your neck, try crossing your arms over your chest or placing your fingertips around your ears. Point your elbows forward or, if you want to make the move more challenging, point your elbows directly out to either side.
4. The problem: You relax on the way down.
"A lot of people will work hard on the way up and then relax on the way down," Hoebel says. "If you do, you're skipping out on half of the work—and benefits."
The fix: Squeeze your abs to lift yourself off of the floor and, on the way down, just keep squeezing, he says. Focus on using your abdominal muscles to slowly lower yourself, rather than drop, to the floor.
5. The problem: You hold your breath.
Deprive your body of oxygen and your crunches are going to get a lot worse, Brennan says.
The fix: Exhale on the way up and you'll automatically breathe in on the way down, she says. Bonus: If you forcefully exhale during your crunch's contraction, you'll also activate your deeper abdominal muscles during the move.