Why Leg Raises Contribute to Back Pain

About 30 years ago we learned that straight legged sit-ups were bad for us because it caused back pain.  But aren’t lying or hanging leg raises the same thing as the straight legged sit-ups – done in reverse?  Aren’t we using the same muscles, whether we raise our legs and keep our upper body still or raise our upper body and keep our legs still?
 
Great looking abs are desired by both men and women, but lying or hanging leg raises are probably one of the worst exercises you can do.

Why it’s bad…

To understand why this movement is bad, you need to understand the basic biomechanics of how muscles contract to move the body.  Basic anatomy and physiology teach us that a muscle attaches at two ends. When those two endpoints or attachment points move closer together we get muscle contraction.  It is the contraction of the muscle that pulls the endpoints closer.  When the two endpoints move further apart, the muscle stretches and relaxes.

Look at the bicep muscle, for an example.  It attaches at the top of your shoulder and just below the crease of your elbow.  When you bend your arm or do a bicep curl, the two endpoints move closer together, and the muscle is in a state of contraction.  When you straighten your arm the two points move further apart and the bicep muscle stretches or relaxes. 

Every muscle in the body works by this same “pulley” principle, including our eye muscles.  Look at the chest muscles.  The pec’s attach along the side of your sternum and run diagonally into the top of your shoulder.  As you lower the bar when doing bench press, the two endpoints move further apart.  The pec muscles are stretching, but as you push the bar off your chest, the two endpoints move closer together.  This causes the pec muscles to contract.

Examine the leg raise….

The muscles primarily responsible for raising the legs are the psoas muscles, NOT the abdominal muscle. The common name for the psoas muscle is the ‘hip flexor.’    The hip flexor attaches at the upper/inside portion of your thigh muscle and sits beneath your abs and intestines and runs up and attaches to your spinal column, more specifically your lumbar vertebra and disc.  These muscles are notoriously known and commonly overlooked for being a primary cause of back pain.

The abdominal muscles attach at the bottom of your ribs and run down past your belly button and attach to the pubic bone.  Remember, a muscle contracts when the two endpoints come closer together. 

To prove to you that lying or hanging leg raises don’t specifically work the abdominal muscles; let me get you to lie flat on your back as if you were performing a leg raise.  Place your right hand at the top of your pubic bone and your left hand on the bottom of your rib cage.  Now slowly raise your legs up to the ceiling, no more than 90 degrees.  Did your hands come closer together?  I don’t think so!

If you keep pulling your legs past that vertical position (90 degrees) and move them closer to your head, you will notice that your pelvis will begin to rock up towards your head.  You should begin to feel your hands move closer together. This is because you are finally contracting your abdominal muscles.  You are basically doing a reverse crunch.

If you keep your hands in the same position and do a regular crunch you will notice your hands move closer together, which tells us your abdominal muscles are doing the work.

Hopefully, this will help explain why crunches and reverse crunches are some of the best exercises for your abs.  Doing leg raises, or holding your feet six inches off the ground or having someone throw your legs back down after you raise them is only going to make your hip flexors tighter and put you at risk for back pain.

I see patients come to my office complaining of back pain.  I ask them if they sit all day. Sleep in the fetal position? Sit for long trips? Along with what kind of ab workout they do?  If they say, lying or hanging leg raises or some other type of similar movement, I help educate them why it isn’t a good exercise to do.

In Summary…

When you do a leg raise the first 90 degrees of the leg raise is activating the hip flexors, when you go past 90 degrees, the abdominal muscles begin to contract and are responsible for raising the legs even further.  Unfortunately, most people only do there leg raises within that first 90 degrees of range of motion, which is only going to make them susceptible to low back pain. 

It doesn’t matter if you bend your knees, or put your hands behind your back.  The muscles responsible for raising your legs those first 90 degrees are your hip flexors, NOT your abs.  Go grab an Anatomy & Physiology book and take a look at where these muscles attach to better see what we are talking about. 

Next time we’ll discuss why aerobic exercises equipment is great for conditioning but not for toning our glute muscles.