After a long cycle, say 40mins, my lower back starts to hurt. In seeing a professional to have a proper fitting I was told when sitting on a bike I basically need to push my butt out, hold in my stomach and have an open chest, bent arms, the way he demonstrated it kind of looked like doing a squat. I thought ok, if that's the correct way, but I don't see anyone else cycling like this. Watching Triathlons on tv, people on the street they all have an arched back, which I was told not to have. Might I add this new position is very uncomfortable, but I guess I need to get used to it.

Does anyone else get lower back pain??

I wouldn't have thought you should be experiencing significant pain. As with running, if you persist with a painful technique for too long, you're likely to do yourself an injury.

I'm not a professional, but it sounds like you're having to bend over too far to reach your bars. If your seat position is correct for you, I'd suggest raising your bar height. This will make you more upright which will not do much for your aerodynamic efficiency, but unless you're cycling competitively I wouldn't worry about it.

Other than that, work on your flexibility and over time you may be able to get down further.

Also, I've found this website (http://www.cyclingnews.com/fitness/?id=default#qa) good for cycling related questions. Answers are from industry professionals and very informative. Have a search through the archives and you'll find an answer.

Make sure your bum is on the saddle as much as possible, oh and dont sit on top of your hands, I've found it makes it very difficult to steer!

My lower back is quite stiff, so I used to bend too much up higher in my back when I was cycling. It is BAD! After a while I'd start getting real sore right where I was bending over to reach the bars.

Now I ride more like I suspect you've been told, with a flatter back. It only took a couple of rides to get used to it, and it's more comfortable now.

One thing I found I had to remember is that the bike has a saddle, not a seat. Don't try to sit on it like it's a chair. You have to remember to roll your pelvis forward to avoid having to arch you back to reach the hoods or the drops.

And don't pay attention to the tri's on TV, most of the ITU crowd have horrible positions!
--Toby