Squats: lumbar hyperextension

[Eldo]

Mark,
I'm doing the Starting Strength workout together with my buddy since about two month. Recently I experienced more and more pain in my lumbar spine relative to the weight used during the squat work sets. What may be quite important to mention here is that I feel this pain not during the set. It starts after it and becomes more intense during the rest of the workout and at home. If I inhale very deeply I can feel it the most.

My first assumption was that my lumbar spine gets round at the bottom of the movement due to a tight hamstring (or weak spinal erectors). I told my buddy to watch out and be very careful if there is any flexion. He always said there is none, he only saw a "light hyperextension". I somehow did not believe him, I always thought he overlooked the flexion somehow.

In order to figure this out I took of my T-Shirt today and squatted beside a mirrow at home and taped it with my camera. And there really is a clear hyperextension. I wasn't able to feel it before due to a lack of kinesthetic sence. Even if I try to raise my chest as high as I can and inhale the most large amount of air I'm able to do I still hyperextend my back. It seems like my abs are not strong enough to enable a tight back.

I read here on the boards that you have only discoverd this with thin, hyperflexible females. Well, I'm male but I'm also very thin (71kg/1,95m) and quite flexible (I'm dancing). What would you recommend me to do? Work on my abs? If so, what exercise? How should I continue with the rest of the workout?

PS: I know that you think that the abdominals are trained isometrically during the Starting Strength workout. This is also one thing I don't understand. My abs should have developed with the rest of my muscles.

[Mark Rippetoe]

First, post a video so we can see if your assessment is correct. Sometimes it can be wrong if you make the judgement yourself with no experience to interpret what you see.

Second, your abdominals are trained isometrically in the squat if they are in contraction when you squat. If you are actually in overextension they will not be in a hard contraction and can therefore not be trained effectively in a position you do not assume.

Third, gain some weight, about 50 pounds. This tends to stabilize the spine.