Sorry if this post is a little technical and boring. I had a request (yay!! thanks!!) to pass on some of the things I have learned on my saddle fitting journey. I'll try to make it semi-amusing. Or at least amusing to me :) Disclaimer: I am NOT a saddle fitter. All I have to say is based off of my personal experiences and research.
You have to start with the basic understanding that whoever first decided to jump on a horse and ride was a lunatic. Seriously. Who thought of that? I rank that up there with the first person who decided eating an egg was a great idea. Can you picture that? Look, a bird just crapped that hard thing out of its body. Lets go and eat it! Yum! You know it was fertilized. And they probably tried to eat the shell too the first time. And raw. Gross. But putting that aside, looking at the make up of a horse they really aren't made to carry us around. They just so happen to have been found useful to do so. Over the course of history saddles have changed dramatically as horses became more than just a useful tool that when no longer able to perform the task at hand was easily discarded and replaced. People slowly began to care about the horse and proper saddle fit slowly followed. Or at least that's my history of it. I'm sure there are a lot more specifics behind it.
There are basic principles that most people understand to be true. The saddle goes on top. Check. It needs to be secured somehow and so the girth was made. Check. To avoid rubbing and pain a pad is needed. Check. Great. Lets go ride! If only it was so simple. Here is what I have learned and keep in mind this is centered around my issues with Gem and around English saddles.
Does this really matter? You bet it does. Lets look at Pete versus Gem. Pete has a nice long back. His saddle sits comfortably behind his shoulders and in front of the last rib where it should. Nothing impinges in the back. Gem, being an Arabian and therefor having 1 less vertebra in her back by design (well, by human design anyway), has a short back. A long saddle will not only sit on uncomfy flesh behind her ribs, but will also be hit by her butt will every stride which is even worse at the canter. This will push the saddle forward. If you are a larger person, you may be limited in saddle seat size by your horses back size.
Fix: Short saddle. But if you need a longer saddle, make sure the panels flare upwards in the back. This will give room for the butt to move up in canter and not push the saddle over the shoulder in the front.
Nobody likes pressure directly on the boney spine and your horse doesn't either. The channel width (space between the saddle panels) needs to be wide enough to span the spine and sit comfortably on the back muscles on either side of it. For Gem this is 4 fingers widths minimum. Other horses are narrower. Check by pushing on the spine and moving slowly out and down. Once you hit soft flesh, stop.
The most notorious part of saddle fitting. This is the width in the front. Too narrow is a big no, no. Too wide isn't so great either but can be dealt with. How doe you tell? The most important factor is clearance of the wither and shoulder. With the saddle on the back, is there room between the horse and the saddle pommel (front edge)? No, it is too wide. If you can drive a semi through it, too narrow. Now run your hand between the saddle and the body. Does it move smoothly or does it pinch? One last quick and dirty test is to put the saddle too far forward and slide it back until it rests nicely. Take a step back and look critically at it. Is the seat nice and flat? If it is tilting back, the saddle is too narrow. This is due to it not sitting down onto the horse pitching the front upward. When you ride, you will be fighting a tendency to lean back. If the seat is tilting downward, the saddle is too wide. You will ride leaning forward.
Fix: If too narrow, get new saddle in wider. If width seems ok for the shoulders but saddle is tilting forward, get a riser pad to place under the front of the saddle and lift it up.
Most saddles are fitted while the horse is standing nice and evenly on all 4 feet. That would be great if that's all you did when you got on. Since I am assuming most people actually move somewhat while on the horse, this will fall apart quickly. When the horse extends a front leg forward to walk, the shoulder blade rotates backward. How much depends on the horse. You can check for this though. Mark wit chalk the back end of the shoulder blade when standing still and square. Ask a friend to extend one front leg forward. Watch as the chalk rotates backward. Repeat on other side. When your saddle is in place, the shoulder needs that much room to rotate or it will be pinched and painful. The horse will take shorter steps to avoid this and be choppy and resistant. While you won't be putting the saddle this far back, you want to make sure it is not tight in the region the shoulder will be when in motion.
Another shoulder fact is asymmetry. Gem has a large right shoulder and small left. Any saddle will need to be fitted for the wider, right shoulder or it will pinch. Fine. I get that. But what about the skinny left side? The saddle will "dig into" the left shoulder and will then slip/lean to the right. It was not so noticeable in my current saddle, but the flex panel saddle was horrible for this.
Fix: Get a pad that allows shims to be placed at various locations. For Gem, I would need to add a shim to the left shoulder to equal that of the right so that the saddle sits evenly on both sides.
My current nemesis. When the saddle sits in the right spot on the back look at where the billets hang down. Now look at the spot where the girth is going to always lie on the horse regardless of anything you try to do to convince it to sit elsewhere. Do they line up? If not, as soon as you girth up and move, the saddle will be pulled forward. It is a big pain in the donkey.
Fix: Ha! I wish I knew. A point billet comes from the front edge of the saddle and allows the girth a more forward position. It will put pressure on the withers. Can't avoid that. But weigh the evils: a little pressure on wither or riding on her neck? When using the point billet, the back of the saddle may become unstable and rise in the air. Use a billet as far back as possible to avoid this. An anatomic girth can be useful, but some just claim to be anatomic while others actually are. Good luck telling the difference. Apparently the insanely overpriced County Logic girth is the best of the best. When mine arrives I will let you know. On that subject, if you are going to use an anatomic girth, it has to be the correct size. If not it will chafe like crazy. But don't worry. Picking the right size is all guess work. Nobody can tell you the exact size or way to measure. So spend your money, use it, return it and try again.
In addition, the length of the billets is important. Look and see where the bulk of the girth will sit in regards to your leg. If you like riding with a super long leg, make sure your billets are forcing the girth buckles to rest right under your leg rubbing your flesh raw.
I can't attest to other issues, such as a sway back, long back, shark fin withers etc...but I can talk about saddle slipping forward issues. That's my problem with Gem.
Other things to try:
A Crupper. This attaches to the back of the saddle and wraps under the tail. As the saddle tries to move forward, the crupper becomes taut and it stops it. Or the horse freaks out due to the pressure and takes off at mach speed. Either way, you are covering good ground and the saddle hasn't moved forward. I haven't tried one yet. I want to wait until the rest is resolved so too much pressure isn't occurring.
A foregirth. This medieval contraption is a strap that goes around the horse right in front of the girth. There are two large bars, hooks, etc...that are on the top and are placed to rest on either side of the wither in front of the saddle. If the saddle moves, it abuts the bars and stops. I have heard these are painful.
Oh! In regards to girthing. I always thought you tightened it all the way. Apparently, I was very, very wrong. The tighter the girth, the more the saddle is likely to move. Huh? Think of a tight rubber band. Stretch it around a water bottle that is wide in the middle and skinny at the mouth. The tighter that band is stretched, the more it wants to go flying off the bottle. This is your girth/saddle. When tightened appropriately, you should be able to get a thumb easily under the entire thing. When you try this, if the back half of the girth feels tight, but the front is loose, take a wild stab at what will happen? It will move forward! This is where crossing the billets can play a role. But, crossing them takes up the space of the billets, so don't try to tighten to the same length as if they were straight or the above scenario will play out.
Well, that's all I can think about right now. If I think of anything else I will let you know!