Activating the transverse abdominis (pulling the stomach inward) is the key to stabilizing your spine when squatting.

This is one of the most hotly debated topics among strength coaches and physical therapists. Personally, I feel that "pulling in your belly" is potentially dangerous when squatting.

When you pull your belly inward, it tends to flex the spine, a.k.a. round your back. This is the last thing you want to happen when you have a heavy weight on your back! After all, unsupported spinal flexion under a compressive load is one of the most common causes of disk herniation. Unless you want to herniate a disk while doing a nosedive onto the floor, I'd advise against pulling in your stomach while squatting.

The correct technique would be to contract your erector spinae (arch your back) and fill your stomach with air by taking a huge breath. Then, hold your breath while forcefully pushing your belly out during the most strenuous phase of the lift (Valsalva maneuver). This technique will not only stabilize your spine by increasing the intra-abdominal pressure, it'll enable you to squat more weight!

Remember that both techniques of stabilizing your spine have their place in training. For example, I feel that learning how to activate your transverse abdominis is a valid and valuable technique during the lifting of lighter loads. It’s also very important for lower-back rehabilitation.

On the other hand, if you’re participating in heavy strength training, I'd highly recommend performing the technique I described above. Remember, attempting a max squat is a lot different than teaching an abdominal crunch to someone who just had back surgery.

Note: Even after this article gets printed, I’m sure this myth won't go away. I just have one request to all of the physical therapists and rehab specialists who'll choose to debate me regarding this topic. I don’t care how many books you’ve read or how many college degrees you have, if you’ve never had a heavy weight on your back, you’re not qualified to argue this topic!

I’ve always found it funny that all of the people who preach pulling in your belly during heavy lifting can’t even squat off the toilet with a newspaper. Practice before you preach!