Hello Zookeeper,

I have to be honest I'm not a big treadmill runner anymore, although I used to spend quite a bit of time on one and I will be running for 24 hours on one in January.

Just an idea that may help out.  I have noticed that most people when running on a treadmill tend to lean forward a little more than when running outdoors.  This is obviously an attempt to maintain a center of gravity as the "ground" moves underneath them.  The lean in and of itself is not a problem however, I have also noticed that most people tend to bend at the waist to add the extra lean.

That can be a problem.  If you are running both indoors and outdoors and your longer runs are outside you may be adjusting your form outdoors to a more erect position.  When you return to the treadmill to maintain your balance you might find that your are bending slightly at the waist.  This bending could be enough to close down your midsection and cause you to cramp.

I would suggest paying attention to this and see if maybe you can lengthen your posture (no bend at the waist).  On the treadmill people tend to bend no matter what the speed just to maintain balance and so it could be happening whether you are running or walking which would explain why it doesn't matter what speed you're going.

Just an idea.  Obviously without actually seeing you run indoors and outdoors its the best thought I can offer.

Give it a try!  Hope this helps.

I have found that no matter how big and nice the tread mill is I still subconsciously check my stride when I use one.  I don't utilize my core muscles in the same way either (as previously mentioned in the above post).  My dad is a personal trainer and he said that not running in your most comfortable stride setting can tend to cause you to breathe differently, changing the way your blood pumps and your lungs work (okay, that's the simplified version...he tried the "real" version and I just looked at him like a deer in the headlights.)