Movement of the shoulder blades and saddle fit
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As we discussed in the last post on anatomy, the back corner of the shoulder blade rotates down and back when the horse extends his leg forward. So how do we fit a saddle behind the shoulder blade and yet not interfere with its movement? This is the practical question that still has not been scientifically researched, but there are some basic facts that make reasonable conclusions possible.
The problem with saddles and shoulders is that we don’t want to squish muscle between bone (the scapula) and a hard place (the bar of the saddle tree). That will damage the muscle and create problems. The long term effect of excess pressure on muscle is atrophy (shrinkage and degeneration), leaving the shoulder blades sticking out from the body with hollows behind them as the above picture demonstrates. It has been known experientially for a long time that severe muscle damage can occur without outward signs on the skin, but a study by GT Nola and LM Vistnes, “Differential response of skin and muscle in the experimental production of pressure sores” Plastic and Reconstructive Surgery, 66(5): 728 – 735, published in 1980 proved this fact. So just because you have no white marks or open sores doesn't mean the muscle underneath isn't damaged.
Three important facts to consider
So if the shoulder blade rotates down and back, and we don’t want to compress muscle between it and the bar, why are we telling you that the bar of the tree (not the skirts on the saddle) should sit right behind the shoulder blade? Aren’t we creating a problem? No - because of three important facts:
#1 – the shoulder blade moves relative to the body.
As we discussed in a previous post, there is no bony connection between the front leg and the body, so the shoulder blade can move against the body wall and tilt and rotate in 3 dimensions, although its movement is limited by its muscular attachments.
#2 – the shoulder blade rotates back when it is unweighted.
Think about how a horse strides. As the hoof lifts off, the leg is back and shoulder blade will be very upright. It is as the leg is moved forward and extends to its farthest reach that the shoulder blade is at its farthest position back. But the foot doesn’t land at that farthest extent. Without weight on the leg, there is minimal pressure between the shoulder blade and the saddle. The shoulder blade is more straight up and down by the time the horse puts weight on it again, out from underneath the bar.
#3 – the shape of the front bar tips of the tree
Unlike the arch of an English saddle that has flat, narrow metal pieces, the bar of a Western saddle is rounded and curved in all directions. This means it isn’t a wall for the shoulder blade to bump into but a curve that directs the shoulder blade to slide underneath.
Putting it all together - how it works in real life
As the leg extends, the shoulder blade moves back. Because it is not solid compared to the rib cage, it has the option of angling in and out as it moves. If the front bar tip is well designed, it guides that back tip of the shoulder blade underneath the bar during the time that the leg is extended the farthest. Because the leg isn’t weighted at that stage, the muscle isn’t compressed. By the time the leg has weight on it again, it is back out from under the front bar tip, away from possible compressive forces. This is how a well designed bar can sit right behind the shoulder blade, not interfere with its movement and not cause damage to the horse. While there are no published papers (yet - hopefully one day!) that show this, there has been unpublished work which shows this to be true.
Bar tip design is important
A big question that still needs to be answered is “What is the ideal shape for the front bar tip?” It is obvious that if it is flat and blocky, it won’t let the shoulder blade slip under. You need to have enough curve to allow this. The opposite - the idea that you can “flare” out the very front of the bar tips enough that they sit over the shoulder blades a bit but don’t touch them - needs more study to see if it actually works or not. There are a few theories as to what may happen under these bar tips, but at this stage, we don’t think they work, though a few other tree makers disagree. There is even the idea that you can “flare” them out so you have inches of bar over the shoulder blade that don’t touch. We are sure that one won’t work in anything but controlled arena circumstances, and probably not even then. It is because of misconceptions about how the tree sits relative to the shoulder blades that we don’t like to use the term “flare”. It can mean too many things to different people. We use the term “relief” because we feel it more closely represents what is really happening under the saddle.
Comments? Questions? Disagreement? Please leave a comment in the section below. (It won't show up right away.) I'm curious about what you readers have to say about all this.
(Later research showing why we need to rethink the traditional ideas of shoulder movement and saddle fit is discussed here.)
Next up - the hind limb.