A festival of anatomy - Hilary Clayton

Hilary ClaytonI had a great weekend at the Horses Inside Out conference (Feb 13/14 2010) and hugely enjoyed listening to Hilary Clayton give a full day of lectures covering the horse’s limbs, back, neck and exercises for mobilizing joints and strengthening muscles.

There was far too much content covered to even try to put it all down on this page but there were a few points that I found particularly interesting:

Range of back motion

I’ve been interested in the amount of (or lack of) movement in the thoracic and lumbar vertebrae since Dr Dave Siemens introduced the concept to me that there is very little movement in this section of the back. Hilary Clayton has used cadavers to estimate the range of motion in each joint of the back. I Googled to see if I could find a picture similar to what she showed us in her slides and found a very useful diagram at the following link: http://nicholnl.wcp.muohio.edu/dingosBreakfastClub/BioMech/BioMechbend2.html

If you scroll down to “Degrees of motion of selected intervertebral joints” you can click through to a version of her detailed finding about the motion found in cadavers. There is only an average of 5 degrees of motion between each thoracic vertebrae and a picture at this link shows how this movement cumulates to give the overall movement of the spine.

My take on this is that its important to remember that the movement of the thoracic and lumber sections of the spine is relatively limited but that there is a movement in this section when you consider the compounding effect of a bit of movement at each joint. The maximum amount of movement takes places between about T10 – T14.

It was also interesting to see the calculations for the axial twist of the spine (the movement that a foal makes to suckle that’s equivalent to us twisting the head to the left or right leaving the ears and eyes on the horizontal.) There is no axial twist possible at all in the joint between Occiput/C1 and a 110 degree movement possible between the joint of C1/C2. This anatomical fact is often mentioned by Mark Rashid as he uses the ability of the horse to twist at C1/C2 to help him release brace at Occiput/C1 in some contexts.

What supports the weight of the horses’ structure and the weight of the rider?

The simple answer is the ligaments. Hilary Clayton quoted some research by Zschokke who took all the muscles off an equine cadaver leaving the ligaments in place. Even without any muscles the structure could still support the weight of a rider. The conclusion is that muscles affect function but not integrity.

The role of the abdominals is to;

Stabilize the trunk
Support the guts (which weight a few hundred kilos)
Flex the back and the lumbosacral joint.
They are not specifically part of the mechanism for movement.

Muscles along the back

Running along the back are the long back muscles, the longissimus and the deep back muscles, the multifidus and the iliocostalis. If the horse experiences back pain the multifidus will be turned off and will atrophy. The deep back muscles are very important for stabilization so its really detrimental when they are turned off. The interesting part is that the muscle will not automatically start to function again when the pain has been resolved. So it specifically needs to be activated by suitable exercises. Narelle Stubbs and Hilary Clayton have developed a series of exercises in the book ‘Activate Your Horse's Core: Unmounted Exercises for Dynamic Mobility, Strength & Balance’ which she spent a whole session of the day talking about. There are some relatively simple, dismounted exercises that anyone can do with their horse to help activate appropriate muscles.

Pliance system saddle mat

Hilary’s team have been doing some testing of saddle fit and rider balance using a Pliance System saddle mat. This has 128 sensors built into a pad that can be placed under the saddle. It shows the amount of pressure at each sensor with a colour coded system. Not only can the pressure of a poorly fitting saddle be assessed but also the impact of a rider leaning backwards or forwards, mounting or turning. Interestingly, the impact of poor saddle fit was softened by a sheepskin pad more than any other pad that was tested. Apparently reindeer pads have the same effect and are cooler!

Rein gauge

Another interesting piece of research that Hilary has conducted, and developed over a period of time, is using a rein gauge to measure rein tension. She discovered that the tension alternates during the phases of the stride, in the trot the diagonal stance phase (weight on the ground for one diagonal pair underneath the body) has greater rein tension and the suspension phase has less tension. Interestingly it didn’t feel like this to the rider to the extent that they originally thought that the readings must be incorrect. The horses were tested without riders and the same pattern emerged.

In Mark Rashid’s work we talk about softness in the reins and a steady contact. For what its worth, there is a slight fluctuation in the feel about 3 times a second. I think as riders we average this feel out and look for the overall feel and softness of the contact but if you concentrate on it you can feel the differences between the stance and suspension phases in the trot.

Bitting study

In a study of bits and bitting, Hilary looked at 4 different bits; a single jointed snaffle, Sprenger Ultra KK, Boucher and a Myler comfort snaffle. A number of different behaviours were shown by the horses when some rein pressure was applied to the bit. These included desirable behaviours such as a quiet mouth and gentle chewing. There were also less desirable behaviours such as opening and closing the mouth (which produces a clanking noise), raising the bit closer to the cheek teeth (and even holding in the teeth), drawing up the tongue under the mouthpiece and finally raising the tongue over the bit which seemed to form a cushion between the bit and the hard pallet.

There was no pattern as to which bit all horses liked or did not like or which behaviour was shown with any particular bit. Hilary was of the opinion that it was the pallet pressure that the horses did not like and she suggests that this is why many of the horses liked the Sprenger Ultra KK bit. You could argue that any of pallet pressure, tongue pressure or bar pressure could be causing the problems.

X-rays did clearly show the very small amount of space in the horses’ mouth between the tongue and the hard pallet. There is not much room in there. X-rays also showed the “Mickey mouse ears” formed by the single jointed bits. These are little curvatures at the joint of the bit which could clearly be seen to make contact with the hard pallet. However I got the impression that there was no clear evidence that the horses consistently reacted badly to this, it was more than the x-ray showed that the contact surface with the pallet was smoother on the Sprenger and Myler bits.

This research is useful in that it provides some great x-ray video of the actual behaviour going on inside the horses mouth (you can see this at the link below) but does not help me to understand from a scientific point of view why it is that so many horses seem to get on very well with the Rocking S bits. I can only think that the stability offered by the design of the rings on the side of the mouth assist with stabilizing the bit so that the movement is not so uncomfortable on bars, tongue or pallet. (See more info about this bit at http://www.markrashid.com/forsale_bit.html).

You can see http://cvm.msu.edu/research/research-centers/mcphail-equine-performance-center/publications for a full list of Hilary Clayton’s research and books. A particularly useful link is http://cvm.msu.edu/research/research-centers/mcphail-equine-performance-center/publications/usdf-connection-1/ where you can see the bit research and x-ray videos of the behaviours discussed. There is also research on a host of other subjects such as mounting problems, sway in horses and the effect of head and neck position on balance, all of which were referred to during the day