[DangerRanch]

Making a separate thread for this discussion. Please forgive the rambling nature of my post. I do not wish to start a fight. I wish only for constructive debate. That said : Bring on your big guns, I've got a thick skin.


What is breakover?
Breakover as I always understood it was the spot on the hoof that is the furthest foreward point on the hoof that is in active contact with the ground, and the last point to leave the ground if the horse were moving with a low stride. Ramey describes it as ‘the spot on the bottom of the foot that is still on the ground at the very moment the heels first leave the ground. (The “push-off” point)”

Now bear with me on a little description of how a horse moves.

I will start with the hind legs as they provide most of the propulsion and then move on to the front later.

Please picture trotting horse.
You start with a flexed hind limb moving the hoof forward under the horse.
The hoof then touches the ground and breaks its forward momentum.
The horses body is moving forward at this time driven by the opposite leg and momentum retained from previous strides. The horse’s weight moves over the hoof.
Several things happen now. Muscles of the hindquarters contract, pulling the joints of the hip, stifle and hock into a flexed position. As the full weight of the horse descends onto the limb the fetlock joint hyperextends downward and back, while the joints between the pastern bones and the coffin bone flex. The fetlock may reach the ground at this stage with enough force. The hoof capsule expands under the weight and is flat on the ground to bear the vertical pressure. All of this flexion serves first as shock absorption but the flexed joints also store energy like a compressed spring.
As the horses body moves further over the leg the large tendon that attaches to the top of the hock, the ‘hamstring’ if you will (or the equivalent of our Achilles’ tendon) straightens the hock and the joints of the hind quarters are released from flexion and straightened, all of which provides momentum to the horse sending him forward and up. As the horses body weight is sprung forward the limb is released from the weight and the lower limb “spring” now straightens and releases it’s energy, sending the hoof into the arc that begins it’s next stride with minimal effort.



The whole time that the hoof is bearing the horse’s weight the entire hoof is flat on the ground. The hoof does not begin to lift until the pressure is released. So that during breakover when the heels leave the ground there is no force placed on the hoof, vertical or other wise. Only a little friction from rubbing lightly on sand or rock. It is simply picked up. This is the only stage of the movement that a long hoof will affect (meaning too long as measured from the back of the heel to the edge of the toe, with a divergent toe angle). There are no lever forces on the toe, because there are no forces on the foot except released kinetic energy sending it upward and forward followed by the pull of the tendons to flex it and move it forward for the next step. What a flared toe will do here is simply make a bit more energy be used in lifting it clear of the surface. The heel lifts at exactly the same moment on a long hoof as a short but the hoof will have to be lifted higher before it can be flexed back. Trimming for early breakover only makes the hoof pick up with less muscular effort. What the hoof does while unweighted has no bearing on how it grows. Flared toes affect the lifting of the foot in the same way ballerina slippers work. It requires more effort to clear the ground and the hoof will travel in a higher arc. This is hard on the horse long term but is not a terror that requires instant remediation. With a balanced trim the flare will be shorter and shorter each time as it grows down and will be soon enough be gone or negligible.

If I didn’t make it clear enough, horses do not push they weight around with the toe of their hoof.

You can get any comparison to a picture of pushing forward with the front of your own foot out of your head. I was disappointed in Ramey for using an improper human foot analogy to discuss breakover. He said:
“There is a tremendous vertical force applied at the point of breakover. This force may sometimes even exceed impact force of landing! Try this experiment: Stand square and face forward, and then suddenly leap to the left or right at a 45 degree angle to the direction you are facing. You will find yourself applying great force to the ball of one foot; all of your weight plus all of your power……….. Now please get back up and do one more experiment for me. Stand square, and then rise up high onto your tiptoes. Now suddenly leap forward at a 45 degree angle to the direction you are facing. Ouch! Sorry about that. Nature gave you a great spot on your foot to leap from, but only one spot. The other parts of your foot have different purposes, don’t they? The farthest forward part of your foot (your big toe) is not your breakover point, it is the ball of your foot. Well the horse is in the same boat, so you’re not alone. “

This is quite incorrect.
Take a look at the skeletal structure of the horse’s hind limb and your own. Your heel is analogous to the horse’s hock. The bones in your foot correspond each to a bone below the hock on the horse, ending with your toe bone, which would be the horse’s coffin bone. Now start the experiment again, this time slowly: prepare to jump. Stop. What did you do? You shifted your weight to the front of your foot and squatted. You may even have raised you heel off the ground. This is the same as if the horse flexed his hock, hip, and stifle. You can jump because you created a spring and have leverage to pull you ankle (hock) straight with your tendon and calf muscles. What happened when you stood up on your very tippy toes is that your ankle was completely straight and useless, and you used the comparatively paltry tendons in the bottom of your foot to move your weight.
You see how the toe was used only a little bit compared to all the power of the front of your thighs, the back of your calf and the force on the ball of your foot (which is the like the horses fetlock. The toe acted as a last little push to send the foot forward, you your body, it also is used for balance and direction. The hoof is not used to move the horse, neither are just a few smallish tendons in the lower leg, the joints and tendons and muscles of the entire hind end are. The hoof adds a little tiny spring upward to the rest of this, it’s primary purpose to hold the weight of the horse and ballance. A horse does not push off with it’s toesthe weight of the horse is springing up away from the hoof as the fetlock rises and the hoof is still flat on the ground. In fact all that tremendous weight down on the pastern would weigh the HEEL more at any given time.(which is why the hoof is the way it is and not turned the other way with the digital cushion and frog in the front.)



The front limb works in a similar manner to the hind but a little different. The flexion of the lower leg is the same, though sometimes it will be greater in the front as the horse carries more weight on the front and the front hoof angle and pastern angle are already lower. The knee remains locked straight the entire time the limb is weight bearing. The shoulder and elbow joint lock flexed. Tendon and muscled pulling the elbow provide some propulsion, though not as great as that in the hind, the front limb is mainly for support. When the leg has moved back underneath the horse the flexed joints in the shoulder are released adding some stored energy back into movement at the same time the knee unlocks and the limb is unweighted , releasing the spring at the fetlock and sending the hoof up and forward just as in the hind. The last push is given to the limb while the hoof is still firmly planted and the fetlock flexed. During “breakover” the knee is loose and there is no weight or hindward force on the hoof at all.

Horses do not push off with the toe of their hoof, pressure is born by the toe of their leg, which is the WHOLE HOOF.


Now for another fun part: The angle of growth
The angle of growth equals the angle of impact. This may sound a little odd at first but listen.
When a hoof is placed on the ground ahead of a moving horse the capsule is moving forward and downward at the same time. A hoof with a healthy heel will place the hoof down flat or slightly heel first. Even when appearing to land flat, on a sound hoof the heel will be the first part to grip the ground. Because there is forward momentum the hoof must brace against the ground to the front or it would slide forward. It breaks with the heel, which is why the angle of growth at the heel is fairly low. For every action there is an equal and opposite reaction. The force of the heel landing and breaking at an angle sends an equal force up the wall along that same angle. Wall horn grows in tubules down the hoof from the coronet and the space between them is filled with horn that grows in sheets perpendicular to the tubules. The angle of the intertubular horn should be be perpendicular to (with the tubules then to parallel to) the angle of the greatest impact for the greatest strength. *
When some of the forward momentum of the hoof has been checked by the heel, the toe begins to grip. The force is now more vertical so the angle of the tubules is steeper. Each impact of the wall on the ground sends vibrations up the wall to the nerves where the wall is formed and the angle of growth is adjusted accordingly. This is why horses vary in their angles and you cannot set a single angle as "correct” for all of them. Every horse moves different. It is essential that the wall be allowed to find it’s correct angle by this natural process or it will continually be “lost” and you will constantly fight divergent angles. Once the initial landing shock is over the hoof bears the weight of the horse vertically with some help from the sole, bars and frog and the cushioning effect of the corium.
Also, you must never mechanically alter the angle of the bone by leaving heels high or trimming them low. The bone is held in place not by the capsule but by the tendons and ligaments that surround it. The capsule rather is held in place by the bone. Trying to alter the natural angle of the coffin bone is like trying to permanently change your hair color with die. You have to do it over and over again and the bone will just keep on putting itself back where it belongs. Even if the position of the bone looks bad to you (club foot) if it was incorrect placement for the current lenght and health of the horses tendons and ligaments the bone would have been pulled right and a correct supporting capsule grown around it. In fact, that is what happens in a clubfoot. Something is imbalanced that requires the bone to be in the position that it is. What the horse needs is not cutting the heels down to lower the angle of the bone but trimming the hoof with the heels in the balance that is needed to support the bone in its current position.


*.If your up for technical reading this is very good: http://jeb.biologists.org/cgi/reprint/125/1/29.pdf also could make a good case from this for not trimming into the natural thickness. The most tubules are in the outer later of wall. They protect from horizontal fracture cracks from rock impacts and such, this is the purpose of the outer wall. The inner wall has less tubules and more intertubular horn, it is meant to prevent vertical cracks (i.e. to be walked on). If the outer wall is rasped away at any point on the top surface of the hoof it will be easier for the now exposed inner wall to crack horizontally. This is in fact exactly what happens if the inner wall is active on the ground and the outer wall is rasped away at the toe (bullnosed), the wall starts cracking horizontally at the toe and breaking away. It also explains why vertical cracks are more common in the outer wall. It is a very good design for hoof wall, the outside is protected from hitting things sideways and the inner wall protects from vertical splits form hitting things on the bottom, and then even if the outer wall splits vertically the inner wall provides a cushion of protection from the vertical crack intruding on the corium.
This is good too for anatomy (and easier reading) : http://www.horseshoes.com/advice/ana...erhoofwall.htm





OK I worked off my explaining itch now, going out to feed.
and probably get a helmet

[Dawn]

I must admit that I skimmed through the last little section of your post as I'm getting ready to get off here.

But the major flaw that I see with your theory is that you are assuming that the horse places his foot flat upon the ground and lifts it straight up flat from the ground. It only takes a few moments of watching a horse in action to realize that this is not the case at all. The horse uses the hoof to push himself forward as the heel begins to come off the ground and as the toe is still in contact with the groud. Therefore, the theory set forth above can not apply by basic nature.

[DangerRanch]

I disagree, I do not see the horse pushing with much force at all on the toe. Indeed the heel does raise first but the knee is already unlocked at the point that the hoof begins to leave the ground and the whole leg is innert and preparing to move foreward and up not back and down. thats as far as the front leg goes. the hind foot does not begin to leave the ground untill the leg is moving foreward either.

[Dawn]

I would beg to differ based upon my own observations of equine movement. Unless a horse is moving very flatly, incorrectly, and with no lift and impulsion, I do not see them as plodding along in this flat footed fashion.

I know that when I'm walking (and yes I'm not a horse, I realize that), the push comes throughout my walk. The heel hits the ground first and starts propelling me forward. Then the foot continues to meet ground level as the limb moves underneath me. The maximum amount of force is located on the ball of my foot just at the moment that the foot passes directly underneath my body, and the heel is lifted off of the ground (the ball of a person's foot would equate to the 'breakover' point on a horse's hoof). Then with continued pressure/force on the toes as the foot completely leaves the ground

In order to not do this, I would have to lift my foot up as it came directly under my body, not allowing it to extend out behind me. The same would apply to the biomechanics of the horse's stride.

[Circle C]

I thought break over was the toe? I have heard "break over" discussed when the shoer was working on a navicular horse... he set the show back and squared the toe ever so slightly for break over reasons???

[JBandRio]

Originally Posted by DangerRanch

I disagree, I do not see the horse pushing with much force at all on the toe. Indeed the heel does raise first but the knee is already unlocked at the point that the hoof begins to leave the ground and the whole leg is innert and preparing to move foreward and up not back and down. thats as far as the front leg goes. the hind foot does not begin to leave the ground untill the leg is moving foreward either.

Front legs do not propel the horse - hind legs do. At the point where the hind limb is coming in front of the vertical, to start lifting the heel off the ground, the hind leg is being it's straightest position, and absolutely the horse is propelling off his toe at that point.

Even in the front legs, as the horse's weight comes over the vertical and the heel starts to come off, the toe is still in contact with the ground for a bit before the knee starts to bend. There is some amount of propulsion exerted there too - that is why many (most?) racehorses have toe grabs - to keep the toe from sliding backwards in the dirt at that moment in time, losing not only forward momentum but that little bit of propulsion.

In a gallop, the leading front leg does indeed hold the vast majority of the horse's weight for some moment in time. Even the non-leading front leg takes an incredible amount of the horse's weight all on it's own. This picture of Secretariat shows it well - the LH is already off the ground, and the RH is so out-stretched with just the toe still in contact with the ground, and even then not weight bearing. This leaves the LF in full contact, bearing all his weight


This picture of the walk, from http://www.tribeequus.com/action3.html#endurance shows how the front right toe HAS to dig in and provide traction, if not propulsion, as well as being weight-bearing, before the heel ever comes off the ground. The toe right at that point is a great leverage point in the movement of that limb. The longer the toe, the more forward the breakover, the more time that foot stays on the ground as the body moves over it, the more stress on the flexor tendons and suspensory ligaments, increasing the chances of bowing a tendon, among other things


So, while I didn't read every single word (you did get long-winded ) I read enough and skimmed the rest to agree with Dawn - I don't see where your theories/arguments hold water

[JBandRio]

Originally Posted by Circle C

I thought break over was the toe?

It is. Where, exactly, depends on what exactly the horse is doing. If he's moving straight forward, the breakover is more or less in the front middle of the toe (depending on how the leg/foot is conformed). But if he's turning, the breakover can be to the side a bit.

I have heard "break over" discussed when the shoer was working on a navicular horse... he set the show back and squared the toe ever so slightly for break over reasons???

Often, when dealing with navicular issues, the problem is man-made - long toes, contracted, sore heels. To help speed progress, the shoe can be "squared" (as in a Natural Balance shoe which isn't really squared, just has a very defined breakover) and set back to put the BO where it belongs, regardless of whether the BO of the hoof can be trimmed to where it belongs.

[DangerRanch]

OK, the short discription of breakover in this article seems to be what you are talking about. (http://old.cvm.msu.edu/dressage/articles/mcpres/MOEL.htm) I would tend to agree with the discription if the hoof was pushing off from the back position with no flexion and extension in the lower limb. this picture is of a limb that is exerting lateral force on a hoof that is weighted and flat on the gound (yet without the flexion of the limb!) and then using the tendons to pull the heel up. I am talking about the spring qualities of the tendons in the lower leg that result from weight bearing. Rather than pulling the heel up and the toe back while the hoof is smack on the ground and moving backward, the mommentum of the horse releases the tendons and springs the hoof foreward, then when the hoof had left the ground it is pulled up.
Picture the tendon as a rubber band attatched to the bones. Press straight down really hard on the cannon bone and the fetlock will be suported by the "rubber band" behind it. Swing the cannon bone foreward as if the horses body was moving over the limb while continuing to push straight down the cannon bone and see what happens when you reach "breakover". When the limb is extended back and the weight is relieved (take the down pressure off and continue moving it foreward) The coffin bone will be sprug forward by the rubber band sending the weight even further forward. the limb is then unweighted and the tendon doesnt have to DO anything. Everything just pulls back into place and the toe didnt do any more pushing than the heel. The toe will be in contact with the ground a bit longer than the heel but the heels is bearing its share just from the fact that the pastern slopes back. the weight would only shift to the toe if the bones were a vertical column.
I allready pointed out that a comparison of human plantigrade movement and the horse that walk on a single bone on the end of his foot is illogical. If you want to do a real feel for how a horse would not have any more presure on the toe than the heel do this:
Take your shoes off.
Place the weight of both feet firmly on the toes and ball with the heel a little off the ground.
Flex the ankle and knee like you are about to crouch down.
Jog around with a springy stepp without letting your heel touch the ground.
You should notice that the greatest pressure just before breakover (the true foreward push) it at the back of the ball of your foot and by the time the ball of the foot comes off the ground you toes are doing nothing but contact the ground, no pushing in any way. they are innert and you leg is springing foreward driven by the mommentum of the push from the leg.


On that endurance horse the direction of force follows the collomn of the cannon bone and forearm. The heel of that foot is weighted as much as the toe. Why else would the foot still be firmly planted like that?

[JBandRio]

The heel of that endurance foot is not weighted as much as the toe - the physics of it dictate otherwise. The tendons have already started to exert some upward pressure on them, and the horse's body is in front of the vertical with respect to where the hoof and leg are, and the momentum is forward, not backward. A disproportionate amount of weight is on the front part of that foot now. You can do that experiment with your own feet. Stand on one foot, and move your body forward and back, without lifting any part of your foot off the ground. The more behind your foot your body is (with a correspondingly backward angled leg), the more weight on the heel relative to the ball of your foot. Leaning forward over your toe, heel *still* on the ground, the more weight, correspondingly, on the ball compared to the heel.