Crunches or Leg Raises for Your Abs

By Dr. Len Lopez
Nutrition and fitness expert

CBN.com – If you are hoping to get your tummy tighter the question that always comes up is which is better, crunches or leg raises? I think the better question is which one works your tummy and doesn’t weaken your low back? The last thing you ever want to have happen if you begin a workout program is to have to stop because of an injury. Unfortunately if you are doing any type of leg raises or hanging leg raises for your abs…you could be making things worse.

Depending on how old you are you may have forgotten that – we stopped recommending straight legged sit-ups years ago, because it aggravated low back pain. Aren’t leg raises pretty much the same thing as the straight legged sit-ups… done in reverse?

To understand why I am cautious about leg raises, you only need to know a little anatomy and physiology. What you need to know is where muscles attach. Once you know that it’s pretty easy to understand which exercise or movement works a specific muscle.

The Basics

Think of your skeletal system like a ‘pulley’ system. Muscles attach to bones and when these two attachment points come closer together the muscle contracts and shortens. If you look at the bicep muscle, you notice it attaches at the top of the shoulder and runs below the crease of your elbow. When you contract and shorten your bicep, your arm bends!
When you look at the abdominal muscles you see it attaches at the bottom of your ribs and at the top of your pubic bone. It’s not attached to your leg, so raising your leg doesn’t seem to really be working your abs, does it?

A simple test you can do to confirm that is….

Lie flat on the floor with your legs straight
Place your right hand along the bottom of your rib cage
Place your left hand at the top of your pubic bone.

These are the two attachment points of the abdominal muscle.

Now slowly raise your legs, it doesn’t matter if you keep your legs straight or bent. Did you feel your hands move? Did the two endpoints of your abdominal muscle contract and move closer?

If your hands are in the correct position, I don’t think you felt any movement!

The muscle responsible for raising your legs are the hip flexors, commonly called your psoas muscles. You can see they attach to the front of your spine and run down to the inside of your leg. Any Anatomy and Physiology book will tell you the action of the hip flexor is to raise the legs or bend forward at the waist.

The abdominal muscles are not the primary muscles involved in raising your legs, at least not for the first 90 degrees.

Stay on the floor and repeat the test, but this time, pull your legs past 90 degrees. Go beyond perpendicular. What happened to your hands? Did you finally feel you left hand move?

It is only when you pull your legs pass perpendicular that your abdominals come into play. Unfortunately, most people who do leg raises or hanging leg raises only pull up to about 90 degrees. In essence they are contracting and shortening their hip flexors, not their abs.
Tight hip flexors are a huge underlying cause of back pain that is often overlooked by doctors, health care providers and trainers. But when you look at where the muscle attaches you can quickly see that it could be one of the muscles that could be at the root of your back problem and needs further investigating.

What about Crunches

To check and see if crunches target your abs go back on the floor and assume the same hand position as before. Now perform a crunch (feet flat on the floor or elevated and raise your shoulders a few inches off the ground).

What you should notice is that your top hand is moving closer to your opposite hand, which means, crunches are specifically targets your abs. Let me also suggest performing a reverse crunch (raise your hips off the ground and keep your shoulders on the ground). You should again feel your abs contracting and your hands moving closer together.

Don’t get mislead into thinking that placing a towel or your hands behind your back or bending your legs will lessen the strain on your low back when doing leg raises. What pulls your legs up are the hip flexors Not the abdominals.

Making your hip flexors any shorter or tighter is not a good thing for most people when you consider most people have tight hip flexors because of all the sitting we do at a desk, in a car or on a plane, not to mention that a lot of people sleep in a curled up fetal position that further shortens your hip flexors.
I have nothing against leg raises, but if you are going to do them do them correctly to minimize any potential aggravation to your low back. I’m a big fan of crunches for helping you target in on your abs. I hope that‘s helpful for anyone who has been struggling with low back pain that isn’t getting resolved.
It’s not about training harder or longer – it’s about training and dieting smarter!

Dr. Len Lopez is a nutrition and fitness expert and creator of the Work Horse Fitness Trainer. His background in natural medicine and strength training gives him that special insight to help those who are struggling to bring both ‘health’ and ‘fitness’ together. You can learn more or get a Second Opinion at www.DrLensBlog.com