Of course, its no surprise that saddle fit very often causes problems for horses. I see it all the time with the rehab horses because even if they had a saddle which fitted before rehab, usually by the time they have worked on a few hills and increased their stride length it doesn't fit any longer.
A flexi-curve tracing of the horse's back at the point where the saddle would sit is a useful way of checking whether the horse is wider than the saddle!
The commonest problem is the saddle being too narrow and tight across the shoulders, like this one. Over time, this causes muscle wastage (as you can see in the photo below) but right from the word go it pinches the muscles which are needed to extend and retract the front legs, especially when you add the weight of a rider.
A shortened stride is inevitable and the horse may well show discomfort by bracing through the back and going hollow or even bucking.
As well as a saddle affecting stride length, there is another place to focus on, which we are often less aware of, and that's the girth. You can see in this photo that there is plenty of room for the elbow to move back without being restricted by the girth but that's not always the case. In fact its possible for shortened stride to be caused solely by girth restriction, even when the saddle fit is perfectly correct.
By contrast, when the elbow isn't going to be pinched, bang into buckles or be rubbed by some hard unsympathetic girth material the horse can fully extend and retract his front legs and take a full stride.
The really good news is that once a saddle is comfortable the horse will immediately respond. This photo shows the same horse as had the muscle wastage and poorly fitting saddle but now he is in a saddle which allows him freedom of movement through his shoulders and back - what a difference!
This is such a massive topic that I will be coming back to it very soon - most likely once I have put together the footage we took of different horses in action with different saddles.
Interestingly, there are many similarities between hooves and saddles.
Poor quality saddle fitting is sadly as common as poor quality hoof care so its not enough to just hand your horse over to a "professional" in either field and hope that they will do a good job. There are an enormous number of professionals in both fields who are routinely leaving horses uncomfortable so as an owner you have a huge responsibility to your horse that you choose the right person.
Secondly, as with hooves, there is a massive amount the owner can do to educate him or herself about saddle fit, spot potential problem areas and help make the horse more comfortable. As with feet, its all about anatomy and biomechanics so while its not rocket science, its up to us to keep educating ourselves.