In part 5 of this series examining the equine hind limb, Dr. Deb Bennett explores hind limb reciprocation.

At the most fundamental level, reciprocation means energy exchange between linked parts of a biomechanical system.

We learned in the previous installment that the horse’s hind limb joints are tied by anatomical straps (in the form of tendons and muscles with tendinous cores) so flexion and extension must occur in coordination. This does not concern the stifle and hock joints only. From the top down, the joints that participate in reciprocation are the lumbo-sacral (L-S) that connects the lumbar spine to the sacrum, the hip socket, stifle, hock, fetlock and coffin joints (Figures 1, 2, 5, 6, 7, 8). In addition, there are joints in the horse’s hind limb, such as the sacro-iliac (S-I), the joints between the tibial and fibular tarsal bones and those between the splints and the cannon bone, but they do not factor into the discussion since are not designed for movement.

The anatomical straps that link the moveable parts of the hind limb together fall into upper and lower functional groups, so that reciprocation in the horse’s hind limb can be summarized by two rules:

1. Whatever the stifle does, the hock must also do. Thus, if the stifle flexes, the hock must also flex; if the stifle extends, the hock must also extend.
2. Whatever the L-S joint does, the stifle is meant to do. Thus, if the horse flexes its L-S joint, the stifle is meant to flex; if the horse extends the L-S joint, then the stifle is also meant to extend. The opposite is more possible than in the lower subsystem, but if it obtains (L-S flexion with stifle extension, or L-S extension with stifle flexion), system components are stressed and can even rupture.

In this series, we have studied the ana-tomy of the hock and stifle in detail, be-cause these joints traditionally have been the focus of hind limb reciprocation. More importantly, however, the above two rules highlight the fact that the hock-stifle linkage (rule no. 1), which is taught in veterinary anatomy courses worldwide, is not the entirety of hind limb reciprocating function, but merely its lower component or subsystem. The upper subsystem consists of the linkages between the stifle and the lumbar, sacral and anterior caudal vertebrae (Figures 6-8). This subsystem is the more important of the two because the L-S joint is functionally the uppermost joint of the equine hind limb and therefore movements of the L-S joint govern movements of all joints below.^1,2,3

The cluster of joints that connect the horse’s lumbar spine with the pelvis and tail. A: lateral view, head to right; B: view from in front; C: view from above, head to bottom of page. The pelvis fits over the sacrum and last lumbar vertebra as a lampshade fits over a lamp. The L-S and intertransverse joints permit loin coiling and uncoiling (flexion and extension), while the S-I joints permit almost no movement.

Unfortunately, the lumbar-to-stifle connections and functioning are not emphasized, or even mentioned, in all veterinary anatomy courses. Some veterinarians have expressed to me that they believe (for example) that there is no connection between the supraspinous ligament and the sacrum (an error of fact; see Figure 7). 

Indeed, the importance of the equine spine in locomotion has been an absolute blind spot for some authors.4,5 Smythe, for example, opines that the horse has an “almost rigid spine incapable of any useful degree of flexion,” and considers that equine locomotion is carried on almost entirely by the limbs that serve “to hoist a bulky, heavy, and unhelpful body” along the racecourse or over jumps.

A more accurate view is expressed by Goody,⁶ who diagrams the upper subsystem. Goody is also almost the only author to correctly describe the crucial role of the tensor fasciae latae (TFL) muscle in unlocking the stifle and in preventing it from locking during locomotion (see “Unlocking the Value of the Oddly Designed Stifle” in AFJ’s November 2021 issue).

The total flexibility or up-down range of motion of the free span of the horse’s back is about 4-12 degrees. Nonetheless, its elastic oscillation is crucial to normal equine locomotion. Contraction of the muscles attached below the vertebral chain (rectus abdominis, the ilio-psoas complex, and the longus colli and scalenus) empowers upward bowing (flexion, coiling) of the back, while contraction of muscles attached above the vertebral chain (primarily longissimus dorsi) cause the back to hollow (extend, uncoil). In collection, the back oscillates both upward and downward; collection is maintained even when downward oscillation is large (as in the dressage movement called passage or as in the extended phase of gallop), so long as the back elastically rebounds upward again with each stride. Collection is lost and movement becomes abnormal when the muscles along the topline remain in contraction all the time and thus act to “freeze” the back into the extended position (see Figures 11b, c).

Excellent anatomical images also appear in Sisson and Grossmann’s classic work,⁷ together with helpful observations of the functioning of the L-S joint and posterior parts of the dorsal ligament system (the student has to dig for these, because they are largely hidden away in footnotes pertaining to the individual ligaments and muscles).

Hildebrand¹ makes the tie between the oscillations of the back and the functioning of the hind limbs even more clear. He and virtually all other authors who have studied spinal function in horses base their thinking on the “bow-suspension bridge” model of spinal function first proposed by Slijper in 1946,⁸ which is also antecedent to the model that I present here (Figure 5).

The Collection Connection

If memory serves me right, I received an invitation in 1986 from the American Farrier’s Association to give a presentation at their national convention. The event was a lot of fun, and I’ve had quite a few farriers take me aside over the years to say they enjoyed it and still remember the subject on which I spoke: the relationship between equine spinal function (the degree of collection) and hoof strike, hoof wear, and hoof growth.

A Thoroughbred skeleton showing multiple spinal fusions, including “kissing spine” (which welds adjacent dorsal processes together) and “bec de paroquet” (which welds the ventral aspects of adjacent vertebral centra together). This horse could not flex the spine at all, either dorso-ventrally or laterally Therefore, its hind limbs would have swung back and forth like broomsticks, without much or any stifle/hock flexion.

Great strides have been made since then — most importantly, it is now generally recognized that back dynamics and limb dynamics are mutually interactive in equine locomotion.9 This includes the realization that the elastic up-and-down oscillation of the horse’s spine with each step it takes not only affects its hooves, it also determines the likelihood of upward fixation of the patella (UFP) and delayed patellar release (DPR).

The horse may engage its stifle-locking mechanism volitionally at a standstill, which is normal and harmless — or the mechanism may engage unexpectedly while the horse is moving, which is painful, frightening and often physically damaging to the animal. As we have already learned (AFJ November 2021), in UFP the patella locks fully, permitting no stifle flexion. In DPR (“sticky” or “rubbing” stifles), the patella-patellar cartilage unit (the PPC unit) is released late, so it gets dragged over the medial epicondyle of the femur as the stifle begins to flex.

It is worth asking why these problems are chronic in some horses, occasional in others, but do not manifest in many. This question is answered in this article, which ties everything we’ve learned in this series together by highlighting the reciprocation between spinal dynamics and the functioning of the entire hind limb.

A biomechanical model of collection in the horse: the spine considered as a set of cantilever bridges.

Functional Zones of the Equine Spine

The spine is part of the axial skeleton (the limb bones comprise the appendicular skeleton). This includes not only the spine but the skull, teeth, jaws, hyoid bones, ribs, rib cartilages and sternum (Figure 1).

The spine is divided into sections — cervical, thoracic, lumbar, sacral and caudal — each of which is made up of a chain of vertebrae of similar form, which therefore have similar movement capabilities. In toto, the cervical joints (green in Figure 1) permit five kinds of movement: translation or side-to-side slippage (only at the poll joint), rotation about the long axis of the spine (only at the joint between atlas and axis), flexion or upward arching (all except at the atlas-axis joint), extension/inversion (all; downward sinking/hollowing) and lateral flexion both left and right (all except at the atlas-axis joint).

Closeup study of the connection in equines between the lumbar spine and the hind limb, lateral view with head to left; superficial layers. The lumbo-dorsal fascia is a large, thick, somewhat rubbery sheet that covers the whole of the horse’s back from the withers to the sacrum. It gives rise to multiple leaves in different body zones (for example, the dorso-scapular fascia which we studied in “Examining the Shoulder to Thorax Junction,” in AFJ January/February 2020). In the hindquarter it extends over the whole width of the back and rump and bridges over the L-S joint. It is shown here in cut section so that underlying structures can be seen.

The gluteus medius is the largest of the three gluteal muscles and the only one to bridge over the L-S joint. It originates on a tough connective tissue sheet covering the underlying longissimus dorsi muscle, on the sacro-sciatic and sacro-iliac ligaments (see Figure 7), and on the upper surface of the ilium (the wing-like fore part of the pelvic bone). The longissimus dorsi is the largest and longest muscle in the horse’s body. It extends from the anterior thorax to the ventral margin of the ilium. It is shaped like a thick bolster supported by the shelf formed by the ribcage and lumbar transverse processes.

When actively contracting, the gluteus medius both retracts the hind limb and extends (uncoils) the L-S joint. Likewise, contraction of the longissimus dorsi powerfully extends the back. However, as we learned in “From Interosseous Muscles to the Suspensory Apparatus” (AFJ November 2019), when a muscle is not contracting but its antagonists on the opposite side of a joint are doing so, then that muscle acts like a yellow ligament. When the horse coils its loins, the gluteus medius and longissimus dorsi are not contracting and they then work as part of the “blue cables” in Figure 4 to round the back and cantilever the forequarter.

As we pass section by section caudally, movement capabilities become fewer. The thoracic vertebrae (blue) can move in only three ways: flexion/upward arching, extension/hollowing and lateral flexion (there is also a “coupled rotation” that occurs with lateral flexion; see Townsend et al.10). 

The first three lumbar vertebrae (pink) are similar to thoracics in that they can flex up, down and to either side, but the last two or three develop articulations between the “wings” or transverse processes (Figures 2, 6, 7), which prevent lateral flexion. The posterior lumbar vertebrae are thus capable of only two classes of movement, flexion/upward arching and extension/hollowing (coiling and uncoiling). Coiling of the lumbar spine from the L-S joint forward is the most essential determinant of collection, as well as governing the degree and timing of stifle joint flexion and thus hindlimb reciprocation (Figures 4, 5, 10, 11).

The sacrum (red, Figure 1) is made of five vertebrae that are fused in the adult horse, and thus no movement at all can occur within the sacrum. It functions like a pump handle, a lever that anchors the muscles, which coil and uncoil the L-S joint (Figure 6). As a unit, it can make one type of movement: up/down. Collection would be impossible if leverage was not provided by a stiff, rodlike sacrum.

Closeup study of the connection in equines between the lumbar spine and the hind limb, lateral view with head to left; deep layers. The psoas minor muscle, along with the iliacus (not shown) and the rectus abdominis contract to pull the pubis forward and effect flexion at the L-S joint. The pull is simultaneously transferred to the sacro-sciatic sheet, so that the sacrum and anterior caudals are pulled downward with the pelvis. Likewise, the pull is transferred from the ischium (rear part of the pelvis) to the posterior caudals via the upper head of the semitendinosus (STM) muscle and to the sacro-sciatic ligament by the semimembranosus muscle (SMM). Downward rotation of the pelvis and sacrum in turn pull upon the “blue cables” — the dorsal and lateral sacro-iliac and supraspinous ligaments (and the lumbo-dorsal fascia) — tautening them and transferring the effort of collection forward from the hindquarters to the base of the neck, as shown in the model of collection (Figure 4). Upper head of STM muscle shown in cut section.

The sacrum is made functionally longer and thus more effective (a longer pump handle) by the first two tail vertebrae, which are stouter than the others and joined to the rear end of the sacrum by heavy ligaments that sometimes ossify, thus cementing them to the sacrum (Figure 6). The part of the dock that appears from the outside to be free of the body is structured internally by the rest of the tailbones. The joints between tailbones are formed as simple, rounded bumpers (Figure 2), enabling the tail to take on the shape of a rainbow arch, an inverted “scorpion-tail,” or for sections of it to counter flex and thus to appear kinked. Due to its relative thinness, the overall flexibility of the fleshy tail is greater than that of any section of the spine except the neck, but nonetheless its movements are limited to up/down and side to side.

The elasticity of spinal oscillation is mediated not by the intervertebral joints only, but by the fact that they are enwrapped by layers of ligaments, and these in turn are covered by the long musculature that runs parallel to the spine. The horse’s spine is thus not rigid,^4,5 but stiffly elastic somewhat like a diving board.8,10^,11,12,13

Numerous attempts have been made to measure spinal oscillation,^{14,15,16, 7} and although techniques and results differ in studies, all agree that the maximum degree of oscillation is not very great. Nonetheless, the back is not rigid like a tabletop and the up-down flexibility that is possible — something between four and 12 degrees of amplitude — is absolutely crucial to normal locomotion. Any horse whose back has become rigid (through arthritic changes, for example, see Figure 4) displays movement that is abnormal.18,19^,20,21

Closeup study of the connection between the lumbar spine and the hind limb, view from in front and slightly below. The psoas minor and the pre-pubic tendon are shown in perspective view (extending to front), as are the sacrum and anterior caudals (extending to back). The sacro-iliac joints permit little movement; they act rather to stabilize and anchor the horse’s spine to the pelvis. “Coiling of the loins,” the key effort of collection, is affected primarily by flexion between the central and lateral facets of the S-L joint formed by the articulation of the last lumbar vertebra and the sacrum.

A Cluster of Crucial Joints

The horse’s hind limb is joined in a complex way to its spine. The sacrum, last three lumbar vertebrae and the pelvis articulate at five key points that cluster in a zone about 8 inches long and wide near the peak of the croup (Figures 2, 8). Three of these joints (marked in pink) comprise the L-S connection and are meant to move. The inter-transverse articulations, which occur where the transverse processes of the last two or three lumbar vertebrae abut, are marked in blue. They work with the L-S articulations in coiling and uncoiling the loins. Like the L-S joint, they are capable of almost no lateral flexion nor of any movement except coiling and uncoiling, and they are the joints that govern both collection and stifle flexion.

The left and right sacro-iliac joints (green in Figure 2) stabilize the pelvis and fix its position relative to the sacrum and lumbar vertebrae. These joints are frequently the target of chiropractic manipulation, because horses can sprain the short, stout ligaments rimming these joints that serve to hold the pelvis and sacrum together. When that happens, there is pain and swelling, and often as a sequel, misalignment of the pelvis with respect to the vertebral chain. This can occur in any dimension or in all three. That is, the pelvis can be twisted laterally so that (in a horse) one hipbone comes to lie in front of the other, it can be rotated so that one hipbone lies higher than the other, or it can be steepened, so that the front end of the pelvis comes to sit higher relative to the sacrum than nature intended. The latter displacement is the most common and results in the blemish that horsemen refer to as a “hunter bump” or “racking bump.”

Modeling Whole-Body Collection 

Readers who followed our first series (concerning reciprocation in the equine forelimb, AFJ issues September/October 2019 through August 2020) are already familiar with the concept of biomechanical models, which are simplifications of reality constructed to test ideas about function. For example, Slijper’s “bow” model likens the spine to a suspension bridge.8 I have taken this idea — originally intended as a generic model that could be applied to any species of cursorial mammal — and refined it to create a point-by-point match to the anatomical architecture of the horse’s back (Figure 5).

Video images of UFP (view A) and DPR. In both images, the affected limb is the right hind. With full upward fixation, the limb is “frozen” in a relatively extended position, which makes it functionally longer than the other hind limb. If the horse attempts to move forward, he will either hop behind or, more commonly, drag the toe of the affected limb (rarely it is both limbs). With “sticky” or “rubbing” stifles, the patella at first does not release but then pops over the medial epicondylar hook, causing the affected limb to flex suddenly and creating the impression that the horse has stumbled or collapsed behind.

Riding technique has a large and direct effect on enabling — or preventing — the horse from achieving collection under saddle. The rider in view B is unfortunately not very skillful — she hunches, rides with her elbows sticking out, pinches rather than holds the reins and stands on her toes. Like many riders, she does not maintain effective contact because she is afraid of hurting the animal’s mouth (there is really no danger of this). Compare her position and aids with mine in Figure 15.

This hinges on two realizations. First, the back is capable not just of elastic up-and-down oscillation, but also of cantilever function (i.e., the forequarters — centered at the base of the neck — can be lifted up by pulling backward and downward on the blue cables anchored in the hindquarters). The second realization is that there are two suspension bridges involved — a larger one for the back and a smaller one for the neck.

In other words, overall spinal function is also the product of the integration of several subsystems, one pertaining to the L-S joint and sacrum (the anchor), another to the mid-portion between the L-S joint and the base of the neck (the freespan) and a third pertaining to the neck.

The horse shown in Figure 5 is performing a levade, an air of the high school in which the forequarter rises not because it has been horked up by the horse forcefully throwing its head back, but strictly through loin coiling, the deep flexion of the stifle and hock joints and the consequent downward and backward pull that this exerts on the blue cables (the interspinous, supraspinous, and sacro-iliac ligaments; see Figure 7).

No better lesson could be given as to the innate mechanism of collection and the primacy of the upper subsystem of hind limb reciprocation, than to watch a horse lie down. This photo catches my gelding Oliver in the moment of loin-coiling which enables the stifle joints to flex. The horse must flex the S-L joint before he can flex the stifle (and hock) and thus “sit down” behind.

The levade is the paradigmatic collected movement, because in some degree all collected movement is like it, even if the forefeet don’t come off the ground and even if the hind feet are taking steps (Figures 11a, 14). The process of collec-tion is simple (Figure 5): first comes flexion at the L-S joint (red triangle) caused by contraction of the ilio-psoas and rectus abdominis muscle complexes. This steepens the angle of the pelvis (tan bar) and that in turn flexes the stifle joint (and by means of the lower reciprocation sub-system, also the hock). Deep bending of all three of these joints enables the horse to “sit down” behind.

Second comes a strong pull, exerted through the blue cables, which causes the center of the back to rise and also lifts the base of the neck relative to the L-S joint; this cantilevering is the fundamental meaning of “lightening of the forehand.”

Third, as a result of the lifting of the forehand but also the contraction of muscles that underpass the declivity at the base of the neck, the base of the neck rises and the crest of the neck lengthens in a “neck telescoping gesture” (see yellow arrows in Figures 5, 11a, 14).

Here is a description of collection.

• Collection starts from and is always primarily the product of coiling of the loins. It is continued when the free span of the back rises and it is completed when the base of the neck rises (so that the yellow arrows always go forward).

Notice that there is no mention of the head or whether the face is vertical. Neither is there any mention of whether or how much the hocks are brought forward under the body. This is because what happens with the head — and what happens with the hind limbs and the tail — are side effects of the depth and rate of elastic spinal oscillation (the “spinal dynamic”), which is mediated primarily by flexion and extension of the L-S joint.

This is a biomechanical model in the form of a precisely constructed comparative sequence. View B is the original photograph; A and C represent systematic alterations of B’s position produced with the aid of computer. The model, which contains a great deal of information, demonstrates the relationship between degree of collection (flexion of the S-L joint), the likelihood of UFP or DPL, fore hoof strike, and fore hoof shape.

(1) Degree of collection: A shows a collected horse, the others are uncollected. Note the rounded topline and longer appearance of the neck in A (because the horse is making a neck-telescoping gesture, yellow arrow). Horses B and C are tightening the longissimus dorsi and allied muscles, which cause the forequarter to rotate upward and backward — or, equally, the horse drops and hollows its back. This model incorporates 8 degrees of hollowing in C, zero in B, and 8 degrees of rounding upwards in A. Likewise, the horses differ by 4 degrees in the amount of S-L flexion. In A, the pelvic angle is 26 degrees; in B, 22 degrees; and in C, 18 degrees. See Table 1 for comparative measurements of all hindlimb joint angles.

The collected horse is not held together (as B and C are); note the open throatlatch in A and the loose, soft, convex profile of the lower neck. The shape of the extended forelimb differs too: in A, the knee and ankle joints remain softly flexed; in B they are fully extended; in C they are hyperextended. In C, the momentum of limb protraction causes the toe of the fore hoof to “flick” upward, so that an observer standing in front of the horse can see the sole of its hoof.

None of these horses strictly conforms to the rule that in a trot, diagonals strike the ground simultaneously. The greater the degree of collection, the more the forehand will be cantilevered relative to the hindquarters. Therefore the more likely that the contacting (left) fore hoof will break over sooner than its mate behind. The purple line demonstrates the angulation of the contacting forelimb: in A: 116 degrees, B: 128 degrees, C: 130 degrees. This places the fore hoof much farther under the body in the uncollected horses, forcing late breakover and consequent coffin joint hyperextension. The contacting hind limb of a collected horse presses against the ground longer and has more effect in lifting the body than in an uncollected horse.

(2) Likelihood of UFP or DPR: The wider open the stifle joint and the longer the time the joint remains widely enough open for the patella to be pulled as high as the top of the medial epicondyle of the femur, the greater the chance of a problem. The collected horse is safe because, like a cat who runs in a crouch, it always carries relatively more flexion at the S-L joint than does an uncollected horse. The stifle joint is 14 or 15 degrees wider open in the uncollected horses, easily enough to ensure that the patella is pulled high enough upon retraction to “catch” (see Table 1).

(3) False extension of the forelimb: The red dot shows the point on the ground where the fore hoof of each animal will strike. Only in the collected horse does this point lie ahead of the hoof’s position while off the ground. In both others, extension of the forelimb is false because despite the flashy throwing-forward of the limb, the hoof will nonetheless be moving backward as it goes to land (see next section). The old rule of thumb that says that the horse’s toe should never come ahead of the blue line is a good one.

(4) Hoof strike and hoof shape: This model assumes that all three horses strike on the heels rather than the toe. In the collected horse, forces are directed forward: the hoof will strike on the heels an instant before the rest of the horseshoe and will then “roll through” to the toe before breakover and pickup. In the uncollected horses, forces are directed backwards.

The hoof will therefore strike on the heels early and at a steep angle, causing the horseshoe to slam down against the substrate. The shoe, hoof and interlaminar junction at the toe are pushed forward (at heel strike) and then pulled forward (at breakover), resulting over time in the development of perceptible dished toes and a tendency for the heel tubules to be crushed, promoting the development of underrun heels.

(5) The worse a horse moves, the harder it becomes for the rider to sit properly. Uncollected horses force the rider to sit “behind her feet”; only in the collected example do we see her in proper balance (green line). Careful video analysis shows that horses that are hard to sit because they are supposedly “big movers” are almost always bad movers. The bottom line for farriers is that no amount of sophisticated trimming or shoe design can fix this; it is riders who must change.

Deranging the Timing of Stifle Unlocking

Precisely timed firing of the tensor fasciae latae muscle (TFL) is the key to preventing UFP or DPL during locomotion. In terms of understanding why stifle locking or rubbing is a problem with some horses but not others, in addition to post-legged conformation we may now list the other factor that makes it more likely: the failure of the horse to flex the L-S joint and thus “round up” or “use its back” when moving. Why? Because flexion of the L-S joint frees the stifle joint to flex and thus serves to drive angulation into the hind limb from the top — which makes UFP and DPL unlikely. On the other hand, anything that causes the horse to move with a stiff or hollow back, or that diminishes its ability to flex the L-S joint, will make stifle locking or catching more likely. This is modeled in detail in Figure 11.

Graph showing linear relationship between degree of lumbo-sacral flexion and running speed of horses cantering on a treadmill. White circle indicates the degree of error (plus/minus 1.9 degrees). Open circle is interpolated. Data from Johnson et al. (2010).

Stifle-catching occurs more frequently when the horse is trotting than when cantering, galloping or walking. This is because it is possible for a horse to trot (with simultaneous or nearly-simultaneous strike down of diagonal pairs of hoofs) without flexing the L-S joint, or even while holding it in continuous extension^2,14,16 (Table 1). It is impossible, however, to produce gallop or canter without L-S flexion¹⁷ (Figures 12, 13).

Angles measured at joints of trotting horses in Figure 12. Measurements rounded to nearest tenth of a degree. Pelvic angle of this horse when standing = 16 degrees; numbers in parentheses indicate the difference between standing pelvic slope and slope when moving.

Therefore, Thoroughbreds claimed off the track by owners eager to make them dressage competitors are frequent victims of UFP and DPR: the whole life of a racehorse consists of cantering and galloping. This protects the horse from errors of coordination that arise from the TFL muscle’s inability to lift the patella soon enough, long enough or high enough to clear the hook on the medial epicondyle and thus permit the stifle to flex without the patella “catching.”

Racehorses are rarely asked for movements that develop their ability to collect (and the habit of collected movement): both “down” transitions and stepping back one step at a time are completely absent from the training regimen for most racehorses (Figure 14). They also frequently run crooked, that is, with their body at an angle to their line of progress (Figure 13).

Secretariat (checkered hood) is the only horse in this race that is running straight, i.e. true to his line of progression. He did this without having been trained to do so — a rarity. Straight movement lowers joint friction to a minimum, so it is not surprising that Secretariat is also the fastest at 1 ¼ miles.

The dressage rider must realize that what the old masters say is true: the horse must be taught to carry itself straight before asking anything else of it. Further, months of conditioning involving up and down transitions between walk and slow trot, and much meticulous practice involving learning how to halt, step back and work over cavalletti and low gradients will be needed before she can ask for that big booming “extended” trot and have it be safe for the horse.

Here I am on my gelding Oliver performing “one step at a time” backing, a very effective therapy to prevent and ameliorate UFP and DPR. In view A, I have just brought him to a halt out of vigorous forward movement. The resting or conformational angle of Oliver’s pelvis is 9 degrees; in this view it is twice that, an indication that his L-S joint is flexed, his lumbar-thoracic span is rounded, and that he is collected even in a halt. Of course, collection shows through the forequarter also in the arching and telescoping of the neck (yellow arrow).

In view B, I am setting it up to make it easy for Oliver to step back slowly and thoughtfully, one step at a time. He responds by first coiling his loins an additional 4 degrees (his pelvis tilts downward 22 degrees) and then lifting the left diagonal pair of feet. This stepping-back exercise is highly effective at strengthening the muscles (rectus abdominis, iliopsoas and longus colli) that empower collection. Even in this gentle, slow bit of work, Oliver “sits down behind” about 10 degrees (the product of flexing not only the lumbar and L-S joints but stifle and hock also). This is as much as a horse typically lowers the hindquarters in piaffe, jumping or racing trot, yet no special talent or advanced skills are needed and the exercise can be repeated often and worked into any training session.

Effects on both stifle function and hoof shape are determined far more by rider technique and whether the horse moves in collection than by the nature of the trim or the design of horseshoes. The farrier can, of course, work to ameliorate under-run heels or dished toes, but these address symptoms and not the cause. The very best contribution that farriers can make toward reducing the frequency of UFP and DPR is to make copies of this article — and the whole hind limb reciprocation series — available to their clients who ride, train or compete.  

References

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