Back pain when running on a treadmill

Hmm, I don't know the answer, but I have a POSSIBLE idea. This has happened to me and it was because of my spine alignment and just my overall form on the treadmill. Here is how I fixed it:

If I'm on the treadmill I'm usually WAY to close to the front (within a hands reach of the controls and such), which causes my body to be more upright than it should. When you run outside, your body is naturally tilted ever-so-slightly forward, in order to give yourself that momentum and keep everything aligned. When you run tilted a little your spine is naturally aligned and NORMALLY pain-free. HOWEVER, I know that the OPPOSITE can also happen. If you lean TOO far forward, you can get back pain (See: http://www.runnersworld.com/article/0,7120,s6-238-267-268-10426-0,00.html).

Regardless, I think it has something to do with your lean when you run (not sure whether you are going too far FORWARD or too far BACK). Next time you're outside, try to get a really good read of how you run outside, then go STRAIGHT to that treadmill and try to mimic it as much as you can. You may find you need to let yourself move farther back on the belt (that's what I found I had to do - rather than run right up on the control panel which caused my back to hurt and my strides to be unnatural).

EDIT: here is a better explanation of the "tilt" I was talking about - look at the 2nd down in the article. The first picture if what you should look like when running, and what I'm sure you look like when running outside. The second picture is how I used to run on the treadmill - OUCHY! Until I worked out the kinks! (http://www.thatsfit.ca/2009/09/17/chirunning-how-to-run-better-faster-and-injury-free/)

(Another image of the "lean": http://girlevolving.files.wordpress.com/2011/05/running-form.jpg)

Could it be the extra shock absorption in the treadmill is causing you to land differently, actually adding more shock?
Or perhaps making it easier to stride longer, slower turnover time (perhaps 80 outside, 65 inside), which can be harder on the system too?
Or maybe the variation in grade outside and flat running inside is too much?

A study has shown that a treadmill should be set for 1% grade to match flat outside running (wind resistance lacking inside).

Take one last jog outside and try to nail down the actual pace you run, observe and note how fast feet are landing, how exactly, hunched over for moving forward, ect.

Then see how that is on treadmill. Or better, do all that while you run to the gym! And then get on treadmill.

Technically running on a treadmill or outside is one of the worst things one can do to their back/knees , the shock and absorption of it takes their toll. I really encourage you to take up the elliptical for a while until the pain stops. The elliptical absorbs weight and impact associated with running and alleviates it tremendously. Give it a shot and see what happens. Worked for me, good luck!

Ha! This is so not true. If you are running properly with correct form you are not going to be hurting your back and knees. In fact I have run 5 days a week roughly for the last few months and had NO problems. Used the elliptical yesterday and messed up my knee. Your theory is moot.