Monday, February 16, 2015

The Biomechanics of Jumping Position

The Biomechanics of Jumping Position
Alexis Soutter, DVM

  There is much debate these days about the “best” jumping position.  For over thirty years now, it has been very common for riders in the hunters, equitation divisions, and even the jumpers to favor a position in which they lean their upper body well forward onto the horse’s neck.  The most common explanation for this position is that it in some way allows a better release of the horse’s mouth.  Very little attention has been paid in many circles as to what this does to the rest of the horse, however.
  A horse’s center of gravity is slightly variable depending on its build, but is typically a little behind and above the elbow.

  Horses carry 60% of their weight on their front legs, and only 40% on their hind legs. Most riders will weigh at least 10% of their horse’s body weight, so that is not an inconsiderable burden.  If we stay balanced over their center of gravity, the impact we make on their front legs is relatively minor.  However, if we bring that weight forward onto their neck, we are increasing the job the front limbs have to do considerably.  And that’s just on the flat!
   So, now let’s think about what a horse has to do, physically, to get over a jump.  As he approaches the jump, he needs to lighten his front end to allow the hind end to come underneath himself.  This means he shortens his neck, raises his head, and lifts his shoulders.  His weight shifts backwards, and his hind legs coil underneath the body to gather the energy needed to power up and across the jump.  (The next several photos came from a wide range of venues; not all of these rider positions should be emulated.)

  As you can see, as the horse lifts the front end, the front legs are tucked back towards his body, creating a more aerodynamic shape that requires less force for the hind end to propel upwards.

 When the horse pushes off, the hind legs extend fully.  The back also extends, but the horse tries to keep the neck relatively short.  Presumably, this allows the horse to keep its weight closer to the center of gravity. 

  Once the horse is in the air, he extends his neck out to act as a balance arm and help him to “reach” over the fence.  The knees bend and come up, and the shoulder rotates forward.  This is the “bascule” phase of the jump.  The best chance the horse has to get his whole body over a large jump is to arch his back, stretch his neck forward and slightly down with his nose pointing out, and bring all four legs up as close to the trunk as possible.  Horses with tighter legs can manage to jump flatter over larger jumps, but if the jump gets big enough, all horses need to be able to “crack their back” to maximize their clearing ability.

Daryl Kinney on Union

  Next comes the landing.  At this point, the horse needs to reduce his forward momentum.  He raises his head, often quite sharply, to aid in this.  The non-leading leg lands first, followed very quickly by the leading leg.  Both front legs then actually push upwards and backwards to counteract the force of the body coming over.  If they did not do this, the horse would somersault over the front end.  The hind legs rotate forward, and the front end needs to get out of the way as the hind feet touch down.

   Okay, so now we understand what horses’ bodies go through to get over jumps.  How does our position on their back affect them?  That depends a lot on what we do with our own bodies. 
   Let’s start with the takeoff phase.  I rode equitation and hunters as a kid, so I learned, like most still do, to put my body forward onto the horse’s neck in order to get off his back.  Sound familiar?  But think about it – the horse’s center of gravity is essentially right below the saddle.  Adding weight over that area is easy for him to handle.  Adding 100 or 150 or 200 lb up onto his neck – which, remember, he’s trying to shorten in order to get off the ground – makes the rotation of his shoulder more difficult, and reduces the ability of the hind legs to get underneath the body to develop the proper coil. 
   Once the horse gets off the ground, well, now if I’m your average equitation rider I’m going to be putting my knuckles on his neck and resting my body weight over my knuckles.  There is nothing at all wrong with a crest release – but the release needs to come from the shoulder and arm, not from the whole torso.  Remember, your hands weigh next to nothing; but your body from the hips forward?  Not as easy.  As a result, the horse has to stiffen his neck to brace against the added weight, rather than being able to stretch it out and down as a balance arm.  Now, the long muscles of the topline are stiffened and he can’t crack his back into a proper bascule.  So, he has to crank his forearms and his hind legs up higher in order to clear the jump.  This is do-able for most horses over smaller jumps, but you start getting to the 3'6" to 4' level, or higher, and it takes a truly special athlete to be able to do it.
   Now, what about landing?  It’s very difficult, when you are pivoting on your knee and dropping your upper body forward and your heels are swinging up, to then fully correct that when you are landing, as now you essentially need to throw yourself backward.  Some people manage this – but often punish the horse in the mouth or the back as they over compensate.  Other people stay on the horse’s forehand, leading to some ugly landings.  Remember, the horse has to both bring his head upwards and use his front legs to push upward and backward as he lands, in order to keep from somersaulting.  If you’re falling forward on his neck, it just makes his job that much harder.

  Another way to think about this is to imagine an airplane.  In order to take off, the airplane needs to be able to lift the nose in the air, and in order to land, it actually rocks back a little bit, to keep the nose from smashing into the ground.  If all the passengers, engine, and equipment were packed into the nose of the airplane, rather than distributed evenly over the body, how safely do you think that plane could take off, fly, and land?  Not very safely at all, and it likely would not even make it off the ground.

  To finish up, here is a photo of a winning hunter:

  This is a beautiful horse, but I want you to notice a couple of things.  First of all, look at where the bulk of the rider’s weight is.  Her entire body from the knee up is forward of the center of this horse’s balance.  See how the horse holds his neck.  While his nose is poking forward and his rider is not hitting him in the mouth, the neck is stiff and straight.  He is not lifted through the shoulders or the withers, and is clearing the jump primarily because his knees are up and he is tight below.  Notice that his back is a little bit hollow behind the withers (yes, the saddle obstructs this some, but you can tell because the bottom of his chest is dropped below his elbow).  He has just pushed off from the ground, so his hind legs are close to fully extended, as expected. Now, draw the arc his body is taking.  You will see he will have to really hike his stifles and hocks to clear this relatively low jump with his back end.  As a last point, note that her heel has slipped up and back and her spur is digging into his flank.  He must be a good-natured horse.

  Now, look at this picture of an event horse and rider:

Dom Schramm on Cold Harbor


  Notice where this rider’s body is.  He is balanced directly over his foot, which is essentially lined up with the horse’s center of gravity.  This horse is making a beautiful effort over this jump.  The neck is long, arched along the top, and stretched fully.  He is round from nose to tail – note that the underside of his trunk is slightly above his elbows, indicating an ability to engage his abs and crack his back.  And look at how easily he can flex and tuck his hind end!  Look at this rider’s release.  He is utilizing an automatic release, which means he is not dependent upon the horse’s neck to maintain his balance.  Rather than resting on the neck, the hands are maintaining a following contact with the horse’s mouth, which makes it easier to make adjustments on landing.  However, the issue is not crest release vs. automatic release – both can be appropriate in this situation; the goal is to have the rider’s body as easy for the horse to carry as possible. From there, riders can use whatever release they want.

  Think about how much harder to ride the bigger jump is, but note how balanced the rider is.  Who is likely to stay better balanced on landing?  Which of these riders would be more able to help their horse prepare for the next jump?  If the horse should stumble on landing, who would be better able physically to help prevent a fall?  Understanding biomechanics over fences can save your life, and that of your equine partner.

Thank you to Cindy Lawler, Dom Schramm, Denny Emerson, Daryl Kinney and Bob Haarmans for the use of their photos

1 comment:

  1. As a non-jumper, I hadn't thought of this, but the physics of it make a lot more sense when you understand what the horse has to do - and that the human is pretty much dead weight, a weight that can unbalance the horse.

    Kind of like a backpack that is poorly packed when hiking - the weight needs to be balanced and close to the center of gravity, too. You don't want the heavy stuff too high or too low.

    That last picture is very clear.