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Bones and muscle attachments to bones
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David Genadek
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 Posted: Tue Sep 18th, 2018 03:52 pm
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I am wondering if there is a text or app that I can look up a bone and find out what attaches to it quickly and easily.

DrDeb
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 Posted: Tue Sep 18th, 2018 07:38 pm
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David, get a copy of Goody's "Anatomy of the Horse" and make sure it's the latest edition (fourth, I think). There are drawings in there showing each major bone and where muscles or ligaments take root on that bone.

Remember, however, that the MAJORITY of muscles in the horse's body do not root directly upon any bone. Rather, they take origin from tough tissue sheets, called septa, which are exfoliations of the periosteum of the bones. Thus, the diagrams such as I have just recommended, are sometimes rather misleading, because they will indicate that a given muscle originates on a certain area of the bone, when in fact most of the bulk of the given muscle actually originates on the side-surface of a nearby septum.

What question or concern are you after answering with this query, actually? -- Dr. Deb

David Genadek
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 Posted: Thu Sep 20th, 2018 12:43 am
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Specifically I am exploring the shoulder as it relates to saddle fit so I am asking the question when they design a saddle to use the Latissimus dorsi as a major support muscle how will the effects of that manifest themselves in other parts of the body. So I am wanting a simple way to discover relationships. If I place the saddle on the latissimus dorsi how does that affect the humerus and if I affect the humerus how am I affecting the other muscles that attach to the Humerus. So I would like to be able to look up humerus and see what all would be affected.

DrDeb
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 Posted: Thu Sep 20th, 2018 08:33 am
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Dave -- no matter how you look at it, there is no "simple" way to do what you are trying to do. You can look up muscle-to-bone attachments, and you can determine fiber direction and therefore the approximate direction of pull. But "approximate" is the operative term: to take your own example, all the fibers in the latissimus are not parallel; the muscle is large, triangular, and structurally "loosely" pinnate. Its function is to pull the humerus upward and backward. It also moves the scapula and the forelimb as a whole. But knowing this, you also always have to figure out what muscle, or which several muscles, oppose this to move the humerus (and scapula, and the rest of the limb) forward again. Almost all muscles in the body have an opposed (or "apposed") companion that acts to ensure that any given joint "wigs" as well as "wags".

When you get out larger than a single-joint system, the question becomes almost impossibly complex. In a general way, the contraction of any muscle affects the entire body; but depending upon the size, strength, and location of the muscle in question, the effect may be major or very minor.

Just to take one more point too -- how could anyone design a saddle and NOT have it rest upon the latissimus dorsi? The way your query is written makes it sound like there would be alternatives. Are there, and if so, what would they be? Cheers -- Dr. Deb

David Genadek
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 Posted: Thu Sep 20th, 2018 04:53 pm
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I agree it would be impossible to keep a saddle off the lattisimus but we can minimize the negative impact by keeping the surface that interfaces with the horse as high as possible so we are on the sheet that attaches the latissimus to the dorsal ligament more than the muscle fibers themselves. The level of where the muscle fibers end seems to vary quite a bit. It is interesting to ponder the effects of both the trapezius and the lattisimus as they relate to the shoulder.

We can easily keep the saddle off the trapezius which the Mongols figured out how to do by cantilevering the saddle. So we have three pressure distribution themes used in saddles:

1. Pressure front-none in the middle-pressure back (Brida-saddle is placed forward) ,

2. Open front-pressure middle-open back (Jineta and Estradiota/Jineta used a rigid tree to cantilever the saddle so the front stayed open; Estradiota used a tree to shape the seat, and panels underneath to shape the panels for the horse. Those panels were stuffed with rye so they were essentially a bean bag that would shape to allow the openness in the front of the saddle. Saddle was placed foward).

3. Even pressure (rocking horse model saddle was placed behind the scapula. using both the trapezius and latissamus as a support muscle.)

Attachment: muscles email.JPG (Downloaded 30 times)

DrDeb
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 Posted: Thu Sep 20th, 2018 08:29 pm
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Dave, have you seen the recent issue of Equus Magazine, where they are reporting a new study done by Hillary Clayton that seems to show that English saddles made without panels help the rider to balance better? I say "seems to show" because, as I've said before, all results of such studies must be viewed with great caution and reasonable skepticism. Nonetheless the saddles themselves, which are pictured in the report, would likely be of interest to your present line of thinking.

As to variability in where the contractile part of a muscle vs. the noncontractile or tendonous part -- yes, highly variable, and that applies to any and all muscles throughout the body.

As to keeping pressure away from the contractile parts of muscles, yes, agreed, that's important if it can be done. Pressure on the contractile parts of a muscle = gouging, which creates hyper-reactivity and/or tendency to cramp and hence loss of elasticity when the muscle should be in release. Typically in the forelimb this equates to shortening of the step or loss of "scope" and "reach". Cheers -- Dr. Deb

David Genadek
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 Posted: Thu Sep 20th, 2018 08:59 pm
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Deb, I am familiar with the saddle you are talking. We have five surfaces we need to be concerned with when looking at the saddle design: The surface that interfaces with the horses body,the humans foot,the humans thigh, the humans seat bones and the buttocks. How these five surfaces are used or not used determine the different models of saddle design. Mathew Horace Hayes pretty much lays out the whys of English saddle design. The design is for the rocking horse model. The tree creates a frame work of support for the humans seat bones. The front arch establishes the angles of the panels in front but unlike the English saddles cousin Estradiota it does not have an arch in the rear to establish the panel angle in the back. Since the English saddle was originally designed to put you in a chair seat the flaps acted as thigh support. Because we have forgotten the method of riding the English saddle was actually designed for we are trying to ride it like an Estradiota saddle but since the panels were designed for the rocking horse model they are taking on aspects of Brida meaning they are wide in the front narrow through the middle and wide in the back which means the panels lack any surface to support the thigh. So by removing the flaps you can use the horses body for thigh support . In my mind the findings are accurate with in the current consensus reality of English saddle fit but are incomplete from broader perspective of saddle fit. In other words they are trying to make a silk purse from a sows ear.


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