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Straightness with Bend:
Roundness, Engagement, Impulsion, Mobility

Three kinds of straightness are discussed. A horse can be:

Straight on lines and curves (hind legs follow trace of front legs) to enhance mobility: this has enormous consequences for gymnastic training because it is based on the ability to place the inside hind under the inside hip position. This action creates ASYMMETRIC EFFORT for every stride on a curved line because the inside hind of a diagonal is more widely spaced R ---> L than the outside hind diagonal. For the unbelievers, Du Paty de Clam observed this 200 years ago in an argument with La Gueriniere about the benefits of shoulder(s)-in. De Clam pointed out that in lateral work or on curved lines the horse "enlarged himself" (s'enlarger). As a consequence of placement of the inside hind under the inside hip, tracking becomes "straight" by dressage definition of proper position on curved lines, in pirouettes and in all lateral work. The gymnastic horse does not lean in or throw itself over either shoulder at any time. This takes strength, coordination, flexibility in relaxation. If you are still an unbeliever after reading this, go look at digital video movies frame by frame and see that even Olympic horses lean around their corners and on circles... unless they place the inside hind under the inside hip.
Show push and carry capacity that flows evenly from hind quarters to forequarters (dependency on throughness). This type of straightness is revealed as roundness with optimal combination of engagement, bend and impulsion.
Exhibit alignment of all sections of the spine (problems include tilting head, locked sections of neck or "on the muscle," stiff and hollow sides, inconsistent alignment)

Raynyday Smoke 'n Mirrors (3 yrs), trained in hand with my special bitless bridle (leaves jaws, tongue free) as a youngster to perform a few steps of shoulder-in, uses the skill to dominate his older companion Rio Sereno. His bend is clear, as is the asymmetric use of the diagonal pairs of walk.
A horse working on a straight line with no bend has equal effort from each diagonal pair.
Shoulder-in on "
WIDE" diagonal pair, RF-LH.

Asymmetric effort from diagonal pairs on a curved track. This is riding a bent horse on a curved line. Unless guided by an elastic outside rein & stabilized by the outside leg behind the girth, the haunches will "fall out" and impulsion along the curved track is lost. The inside leg maintains the bend and alignment through the center of mass. The spiral seat rider will not lean in, will not twist shoulders or hips to push around the curve (forces haunches out) and will keep the horse on diagonal aids.

Shoulder-in on "
NARROW" diagonal pair LH-RF.

Asymmetric effort from diagonal pairs in shoulder(s)-in. This is riding a bent horse on a straight line. Diagonal aids maintain impulse and bending.

Straight. Center of mass (red outline).

Straightness in all three modes is a fundamental quality of collection. There is a deceptive quality to the external profile of a horse where relative elevation and collection are concerned. This happens because dorsal processes of vertebrae of the thoracic spine are different lengths, being especially tall at the region called the "withers." Check the diagrams below to see that when a horse looks "uphill," the spine may actually be level, making approximately a 90 degree angle at the S-L joint. Because the spine is normally aligned slightly downhill while the horse is at rest or in ordinary gaits, for collection it must lift its center of mass to achieve a parallel alignment of its spine with the ground. This is a great effort for the horse to maintain while in motion and while carrying a rider.

Alignment of three horses compared during Time One (RH in stance) of left canter on free longe.
Class One Levers:
Examples: teeter totters, pliers, crowbars

Class Two Levers:
Examples: wheelbarrows, nutcrackers

Class Three Levers:
Examples: shovels*, brooms*, legs*, arms & backs*. The effort arm is shorter than the resistance arm and multiplies speed at the expense of the ability to exert force.

*This is why cleaning the barn is such hard work!

Right canter seen from the right
To maintain positive relative elevation, a horse must at least lift the mass of its body and forehand. A rider behind the withers has a mechanical advantage over distance 2 (green brackets). The horse can change distance 1 by adjusting its neck. There are two lever systems involved, both are Class 3 Levers: the spine and the legs. Limbs can be regarded as a series of linked class three levers: in this illustration the hind leg is considered as one lever system.

E = effort
F = fulcrum
R = resistance to being lifted (load or mass)

Left canter seen from the right
"X-ray view" of straightness with positive relative elevation and optimal engagement and roundness. In classical equitation there is a specification for "equal bending of the joints of the hindquarters." Looking at sacro-lumbar, hip, stifle and hock (yellow dots) the approximate equality of these joint angles is indicated by the skeletal overlay of the image from the row BELOW (right). The external profile is "uphill" because of vertebral processes of the withers while the spine itself is just about parallel with the ground. The (outside) right hind carries the horse's weight.
A. Straight NO LEANING IN ON CIRCLE - on 8 meter circle left, hind legs follow front legs with balance and mobility because of control of direction and velocity of mass: left bend and axial rotation in rib cage visible. (Raynyday Maximillian, age 16) A'. Straight & Engaged - throughness as push (RH placed for engaged ground covering stride behind) and carry capacity (positive relative elevation/ up through the withers): left hind hoof flat to ground and head profile even.
A. Overbent - some head tilt, nose too far to inside that can overload hind legs: uneven distribution of mass diminishes mobility and throughness. (Vulkan, age 27) B'. Overbent & Over Engaged - throughness incomplete as push (RH well under body but short stride behind with too much flexing of the joints of the hindquarters. Carry (positive relative elevation) capacity strained: head profile showing underside of jaw.
C. Counter bent - left hind leg inside left front leg, ribcage bulges left, head to right: very forward but not particularly mobile. The spacing of LH-RF and RH-LF will be the same as he leans in on the circle. (Raynyday Smoke 'n Mirrors, age 4) C'. Overbent & Engaged - forward with powerful stride behind, but not straight. Showing postive disassociation of LH-RF diagonal: Smoke is not on the forehand! Throughness modest as push (ground covering stride but RH behind hip at this phase of stride) and carry capacity (slight + relative elevation): left hind hoof shightly tipped (leg crossing under body) head profile showing underside of jaw.

The complexity of straightness is illustrated by the way these three horses align themselves. In row A, Max shows balance among right-left front-back balance with engaged hindquarters. Vulkan (row B) is overbent and overengaged, indicating tension in his performance, although he is remarkably flexible (especially at age 27). The young Smoke (4 years, never ridden) is athletic but very inexperienced at adjusting relative amounts of push and carry in alignment. He does not yet have the skill of simultaneously engaging the hindquarters and being up through the withers.

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