An easy way to see how your saddle is affecting your horse, is to put your fingers between the saddle and the horse, at the point of the button.

In the pictures below, the rider is able to put her fingers between the horse and saddle with the treeless saddle; and is unable to get her fingers under the western saddle, in neither front nor back.

If you can't get your fingers under the saddle in the back, the saddle may be digging into the horse's loins.

You should be able to tell if, while the horse is moving, your fingers are being squished, and whether the horse has enough room in there to move freely.

The horse in this picture has a bad back.
As you can see, he's not really a horse that is happy to be ridden.
I've asked the owner to put her fingers under the saddle;
and there's no way that she can get them in there!
So that tells us that the saddle doesn't fit in that area,
that the horse doesn't have room to move.
You can also do this with the back of the saddle
to see if it's digging into the horse.


Saddle Fitting Guides