Equine Mechanics

Author: Sian Townson

Unmounted rider exercises to improve your seat: Strengthen & straighten your own core.

So whilst we’re looking a little at strengthening the horse’s core, and before we get onto ridden exercises, let’s do the same for the rider. [Ridden exercises for horse’s core here, unmounted for horse core here]

There’s growing research evidence that improving your seat off the horse is a great thing to do because a) it’s effective – who doesn’t want a better seat – and b) you can correct muscle patterns more easily when you and the horse aren’t encouraging each other’s asymmetries. Get your core stability correct, it’ll be easier to get your horse correct. You can spend hours fighting not to collapse at the hip, to sit straighter, deeper, drop your thighs down, toes in and get the horse engaged, to stay with him over jumps, but it’s never going to be as effective as just correcting your own muscle weakness before you start.

Also in exciting news I broke my ankle and so unmounted exercises are quickly becoming my thing. A broken ankle is pretty common in horse riders so this should also help my fellow sufferers whose days are currently filled with repeating “can I ride yet?” I can’t get you back on the horse yet, but at least we can make sure that when you do you haven’t lost all semblance of riding ability, and might even have improved a bit. Might come in handy if your horse has been laying off while you recuperate!

Step 1) Caring: I haven’t broken anything, why do I need to strengthen my own core?

The rider’s seat is an active process. “Sitting on a horse” sounds passive but an engaged seat requires a lot of muscle strength and coordination. Phrases like “go with the movement” are not that helpful as it makes you feel like you just have to find the right kind of wibbly wobby relaxation.

Find something now: a bouncy ball, a sweet wrapper, anything lying around that you can put in your hand and trust to stay completely relaxed. Now, with your object on your palm, bounce your hand sharply up and down, and see how fast you can go whilst it stays in a deep contact by just going passively with the movement. How’s that working out for you?

Imagine an enthusiastic horse bouncing along in trot or canter. Gravity & relaxation are not enough to keep you in the seat when the moving horse bounces you upward. When the horse reaches the downward part of his bounce gravity will pull you back down too but only once you’ve completed your upward trajectory – shortly after the horse stops pushing you up. This means you’ll be catching up with the horse’s back, coming down onto the horse’s back as it starts to re-ascend, with a painful bump. Then he’ll tense up, you’ll tense up, we’ve all been there. Nasty. If you actually tried the bouncy hand exercise, you may have also discovered the urge to slow down to reduce bouncing. Or as we call it “lazy” or “behind the leg”.

You may have known a horse that can go the other way too – rush at a jump unless held by your core. You can try holding them with your arms, good luck with that! To be honest it’s hard to do anything with your arms until you have a stable core anyway, never mind keep your hands soft and following the horse in trot or canter or over a jump.

We the ambitious riders who’d like to own happy horses, want even more than a deep seat that stays on the horse, we want to control our muscle use so that we can move with the horse, even shift our pressure and tension and use it as an aid. No other sport attempts to reach this level of fitness, strength and coordination by just doing the sport. We need to release muscles we’d naturally tighten and tighten muscles we’d not normally use. We need exercises.

Step 2) Addressing the muscles
Iliopsoas: Psoas & iliacus.

The iliopsoas group of muscles is the deepest & arguably the most important part of your core. It’s made up of the psoas major and iliacus. Most people can’t be bothered to say iliopsoas, so they say psoas (the ‘p’ is silent) and mean the whole group, leaving others to get confused and starting to wonder if iliopsoas is yet another muscle. Don’t let it bother you. Similarly some people get het up about psoas minor, but in bipeds (that’s you) it’s so small that it’s often absent, so functionally it’s not the place to focus. We’ll worry about psoas minor when we talk about a [four-legged] quadruped.

Psoas (major) runs from the spine (lumbar vertebrae) to the inside of the femur (or thigh bone), so it flexes the hip and turns the leg out. Ditto iliacus, running from the pelvis to the same femoral attachment, having much the same effect. If you sit in a chair, car seat or anything that leaves you in that thighs up position for an hour or two, your iliopsoas shortens and contracts. So if you have or had a desk job rather than a sitting-on-horses job you’re likely to have issues here. You may even be sleeping for hours every night in a lovely cosy foetal position – or worse, with one leg bent. I’m pretty good at guessing someone’s sleeping position by looking at them on a horse.

If you contract your psoas sitting on a chair, you stay on the chair, albeit with back pain. If you contract your iliopsoas sitting on a horse, you end up with a forward-tilted pelvis, a hollow back (and a hollow horse), and a flexed and outward-turned hip. This means that you can’t get the thigh down or the knees to turn in, because your hip flexors and rotators are jammed on, and to avoid tipping forward you’ll try to sit up by hyperextending & bracing the back. You’re working very hard co-contracting muscles to fight yourself but all you can get is tense, stiff and nasty. Your horse is actually being asked to hollow and you look like a frog.

Even within the very elite, Carl Hester for example has noticeably tighter iliopsoas muscles than his pupil Charlotte Dujardin and so has to work harder to get the same results.

If you’re really unlucky you spend a lot of time sitting in a chair asymmetrically. If you pull more on just one psoas, just on one side, you bend the spine & hence trunk to that side, collapse that hip and are left wondering why you just can’t sit straight on a horse.

If you want to be able to move synchronously with the horse so, for example, in walk your pelvis rocks side to side as your horse does, allowing him to use his back then you need to use your iliopsoas correctly, from a relaxed state.

The iliopsoas group are your most powerful hip flexors. If you’ve ever done knee ups or sit ups thinking you were strengthening your abdominals, chances are these are the muscles you were working. Good news is once you’ve released your iliopsoas muscles your abdominals and inner thigh will naturally strengthen as they’ll actually have to do some of the day-to-day work themselves.

ironically most people’s iliopsoas are both

both tight and weak, because they’re not using the full range of movement. There are lots of exercises online for strengthening the iliopsoas/psoas. Don’t do them. First we want to lengthen and release. There are a lot of yoga videos online on “psoas” release and most of these are very useful.

As the iliopsoas is so close to the diaphragm just breathing can help, and that’s one of the reasons that breathing correctly has such an effect on your horse. Similarly if you tilt your pelvis posteriorly, as if you were trying to tuck your bottom under you and round your lower back, your psoas will already start to stretch and you may feel any lower back pain ease.

It’s very hard to stretch a muscle before it’s warmed up or contracted (despite older advice telling you to stretch before you start exercise) so the best way to start with your iliopsoas is to lie on your back, bring one bent knee up to your chest so that the hip flexors are really short and active. In that position hollow and round your lower back so that you can really target the muscles. Then slowly lengthen your leg out from there until it is flat on the floor and you’ve stretched as tall/long as you can be. Hold for a few seconds. Repeat this a few times on both sides, seeing if you can feel a longer stretch each time.

The second exercise to try is half kneeling and is a little similar to a lunge. Kneel on one knee with the other foot on the floor in front of you, as if you’re going to propose. Then keeping your body upright try to push forward slightly onto your front leg opening your trailing hip to leave the bent leg behind you. This is close to the crescent lunge in yoga, and stretches the iliopsoas of the trailing leg. Same effect can be reached standing up, by putting the front foot on a box/wall/sofa, if like me you find quick standing exercises easier to con yourself into. Just please don’t fall over.

With both exercises repeat 2-4 times both sides, 3 or 4 times a week or as needed.

There are plenty of variations of these and other exercises. It’s ideal to just to think about where the muscle is, and just move in a way that stretches it within your own current ability.

Abdominals

The abdominal muscles get a lot of attention: they’re right on the surface, make your clothes look good and more importantly for us they’re certainly a big factor in making a rider effective. The effortless riders that seem to be doing nothing are using a lot of abdominal muscle strength. Go on, scroll back up to have another look at Charlotte, relaxed but certainly not passive, using a massive amount of abdominal tone to keep Valegro off his forehand and her own body in an effective position. This, along with the pelvic floor, is what is helping pull her down into the saddle even though her horse has pushed her up, and keeps her still so her aids are clear and hands independent.

The tricky part in trying to strengthen your abdominals is that many traditional exercises make it easy to cheat and just use your iliopsoas muscles, leaving you with even more back ache. We’re already great at shortening the iliopsoas, and it’s making us sucky riders. So instead of sit ups and crunches let’s engage core stability and make the abs work in a targeted, lengthened position. If you don’t have a broken ankle you can start the infamous plank – on your hands and knees or hands and feet, as straight as you can as if you’d just completed a push up, but just hold it. Start with ten seconds or two minutes, whatever feels right. Tomorrow you can go ten seconds longer. It’s important to stay within what feels comfortable as if you try to hold it for too long you’re likely to lose the straight back, neutral spine position, and won’t be targeting the muscles as well as you could. If you’re not ready for a full plank you can always use an incline – arms on a sofa or even the wall rather than the floor.

The second exercise to try is similarly starting on your hands and knees, straight back, knees directly below hips. Then lift one hand and one leg straight out and hold it. As with the horse’s exercise the abdominals are working dynamically to keep you stable and balanced, making this a very effective exercise. Similarly if you lift one leg from the plank pose you’ll add a lot of extra challenge to the exercise. In both cases don’t forget to switch and work both sides!

Good news

The great thing about core muscles is that they are unusually quick to train, and not too hard to maintain. The hard part is just the getting started, and you should see results as quickly as the second week.

There is a little more to say about core strength and stability but as ever I’ve already gone on long enough and both family life & paid writing are calling, so I’ll return to this topic in a Part 2. Worth mentioning though, that whilst I’ve used dressage pictures, the core is particularly relevant to the showjumper as it is what keeps you in balance over a jump in a fold. If you struggle with getting ahead or behind your horse, over a jump or in any discipline, or getting him to engage or respond to your aids, a lack of core stability is usually to blame. Ditto ending up exhausted and out of breath when you ride. Often people are just tired because they’ve mostly been fighting themselves. But now we’re going to fix that. Yey us.

September 7, 2015
The Equine Back Part 2a: Core strength, flexibility and balance.

The previous post covered a fair bit about the back’s structure, bones and the issues of carrying a rider. Now I’ll go a little more into the function of the soft tissues and groundwork exercises (keep scrolling) and eventually in Part 3 we’ll get to more on spotting and addressing asymmetry, ridden exercises, and my personal favourite cavaletti.

Musculature

The muscles of the vertebral column can be divided into those running deepest next to the spine, including the multifidus, and those nearer the surface, including the longissimus and iliocostalis. The deepest multifidus muscles run along 2 or 3 vertebrae each, overlapping all the way and connecting the vertebrae to provide support, stabilisation and motor control. They have a lot of innervation so give the feedback that keeps track of spinal position and motion. The more superficial muscles are larger, less innervated and provide gymnastic motion – extension, rotation and lateral motion of the spine. As we covered in Part 1, the interlocking of the vertebrae means that the spine doesn’t really have the ability to bend laterally without also rotating, so these movements require the entire spine, and very little bending at any one single joint.

As well as these muscles that run along and above it, the spine is supported by the ventral muscles running beneath it (flexors) including the abdominal muscles and the sublumbar muscles (iliopsoas muscles). By finding an equilibrium between the two sets of muscles the horse is able to move efficiently by holding the spine in enough tension to support a rider and transfer power from the limbs. The pelvic stabiliser muscles such as biceps femoris and the gluteal muscles help with balance and power transfer from the hind legs and are essential for collection and jumping.

Finally the thoracic sling muscles, such as the trapezius and pectorals, hold the forelimb onto the trunk, and hence when the forelimbs are on the ground can affect the position of the trunk.

If only one side of the thoracic sling is active the position and straightness of the shoulder is affected. Muscle tension through both sides at the same time lifts the withers and sternum, and helps create an uphill horse, lifting the weight off the forehand and rocking it to the hind end.

The thoracic sling is also anchored to the rib cage and used in breathing. This is fine when the horse is still, but when the horse is cantering, for example, he must breathe in time with his stride, and hold his breath when he jumps. Imagine then the problem of a horse trying to relax but not ridden in an regular rhythm.

The model for our groundwork and ridden exercises is Meikle
Rustler, a Welsh Section D who belongs
to Alison Brown and is ridden by her mother Gillian Brown. Rustler competes at
medium level dressage and practises stretches and groundwork exercises
frequently and so has a large amount of muscle tone, making it easier to spot
his muscles activating in response to the activities. Here are some sample pictures of Rustler, who I’ve failed to stand square. I hope they give you an idea of how you can spot these muscles activating during the groundwork exercises discussed below these pics.

Standing ready to
start with muscles relaxed.

Thoracic lift

Stretching

Groundwork exercises

There’s a lot of support in the research for using groundwork exercises to strengthen the back and mobilise the joints both before introducing ridden work to prepare for carrying the weight of the rider, and throughout the career, particularly after injury or time off. They help to improve strength, self carriage, balance, flexibility and the stability needed to collect or jump.

Injured or weak back muscles often do not self-correct and need to be specifically targeted or the horse will attempt to find other ways to compensate, usually by overusing the opposite side, increasing their own asymmetry rather than addressing it. Groundwork exercises can build these muscles back up. Similarly stiff joints and the spinal impingements can often worsen due to continued contact if the joints are not adequately opened and stretched, and range of motion maintained. In the more advanced horse these exercises can improve balance and power needed for collection or jumping.

Groundwork exercises can be roughly divided into three types: mobilising the joints (horse yoga), activating and strengthening core muscles (horse bodypump) and improving dynamic balance (horse pilates). All three are important for a healthy horse. A young horse that hasn’t yet carried a rider, or a horse recovering from injury, would benefit greatly from building up his muscle tone and spinal alignment first but should be careful not to push it too far. At the other end of the scale a horse competing at high-level dressage will need to continue to build these muscles unmounted, but will need to increase the difficulty of the exercises to really challenge his muscles and balance.

Mobility (Stretches)

When a horse is challenged to stretch his spine it opens up the spinous processes and reduces the risk of impingement, and builds the small multifidus muscles that control and stabilise the spine, but often become wasted or uneven as they are not easily activated.

It’s common when doing these exercises that a horse find one side easier than another, and that’s OK, that’s partly why we’re doing them. Better to stay within the range of motion the horse can achieve correctly, then push him too far and encourage him to cheat by stepping or tilting his head. Keep an eye that his ears stay level, and accept that his flexibility, strength, balance and symmetry will improve with repetition. It is not normally worth forcing a horse into a position using manual pressure, as the horse needs to use his own muscles in order to strengthen them, and you risk pushing the horse beyond his current comfortable level of movement if you force it yourself. As with yoga, each stretch should be slow and relaxed, and aim to hold the end position once it’s achieved for a few seconds.

Using a carrot stick or other favourite bait the horse can
be asked to follow the carrot and do the following stretches. Firstly, start
with the stretches which stimulate flexion of the neck muscles, work on his rounding and abdominal muscles and
extend the spine, opening up the processes.

Using the carrot he should be tempted to:

1) bring his chin to his chest,

2) bring his chin down to and/or between his knees and

3) bring his chin down to and/or between his fetlocks.

Start by aiming just to ask the horse to reach towards these
positions, and then with a bit of practise you’ll be able to go further into
the stretch, for example moving his chin between and beyond his knees rather
than just towards his knees. If necessary having a helper put a hand on the
noseband will encourage the horse to keep his head straight, but remember to
tempt him rather than pull him into position.

The second type of stretch are the lateral bending exercises.
These show up asymmetry and further challenges the spine stabilising muscles
and the horse’s rounding and bending muscles. These can be tested by asking him,
by following you with his nose, to one side and then the other, from the front to reaching backwards and
downwards to:

4) bring his chin to his girth,

5) bring his chin to his flank and

6) bring his chin towards his hind fetlock.

It may be helpful to stand next to the horse and ask him to
reach around you to encourage an even bend through the neck and spine. These
exercises can be very revealing as without the added complications of a rider,
and with the motivation of a carrot or other treat, it is much easier to see if
there is a marked difference between the left side and the right. If you have a
helper it can be useful to have them stand at a safe distance behind the horse,
ideally on a stool, to see if the horse bends evenly through his body to both
directions. If you’re not sure if there’s a difference then they’re probably
isn’t, but it helps to take a photo of each direction to help compare them.
Occasionally you’ll see a horse who tries to keep his body straight and just
use his neck on one side, but is happy to bend his entire spine in the other
direction. This is the type of sign of injury or soreness from saddle fitting
or ridden work that may needs further investigation and is worth highlighting
to your vet in the first instance. Every horse will however prefer one side to
the other, particularly if he’s not been challenged to build these muscles
before. An uneven ability to each side but with similar technique is not
necessarily any cause for concern and should improve with practise as these
exercises will greatly increase his range of motion. The horse may initially
attempt to “cheat” by stepping around to face the carrot that he’s
reaching for. It is not worth over-correcting this, after all it’s a fairly
efficient solution to the problem of needing to stretch and wanting to reach
the carrot. Just patiently put him back into position and start again, using a
wall or second person to help hold his hind end still. One he realises which
behaviour wins the carrot he’ll be more compliant in future and eventually
you’ll be able to work in the field, and won’t need to keep lining him up with
the wall.

There are entire books on carrot stretch technique, and they give you an insight into the most accurate targeted activation of specific muscles, but be encouraged that if your horse is moving under his own muscle power whatever you’re doing you will not be hurting him. Even if your technique is different from the next person’s, or doesn’t target the muscles you had in mind exactly as accurately as it could, your horse is still benefiting from doing a stretch.

Correct rounding

Rustler “cheats”
by stepping forward and tilting his head. He still achieves rounding but he has
reduced the difficulty of the exercise.

Lateral bending to the flank. Here we
have a little too much twisting of the neck, whereas ideally his ears should be
level with each other.

Balance

When a horse is forced to keep his balance against a pushing
hand or due to a lifted leg, he must work his core muscles correctly to
maintain his position, just as we would in a sit up, pull up or push up. Young
horses can even struggle to even keep their balance when one hoof is lifted,
and this can be interpreted as irritability at having hooves maintained when
often it is just anxiety combined with a lack of muscle tone and experience
with this sort of exercise.

If the stretches listed above are combined with a lifted
hoof the horse must work to keep his balance, further activating his core
muscles and improving his muscular control. This increases the difficulty of
the exercises so should only be introduced once the horse is already
comfortable with the stretches, and is used to having his hooves picked out.

A hand pressed on the horse’s shoulder or chest for a few
seconds will force him to work his core muscles to maintain his balance. You
may not see him move as you press, but if he’s working correctly you should
notice him rock forward again once your hand is gone. In the advanced horse,
like Rustler, you can combine this with a lifted hoof to increase the
difficulty. You can lift either the front or back leg, but always push towards
the tail, or the opposite hind hoof.

At the other end gently pulling on the tail to one side then
the other can force the horse to resist using (and building) his pelvic
stabiliser muscles. The pelvic stabilisers are the muscles that allow the power
to be efficiently transferred from the hind legs, and help to keep the horse
balanced and off his forehand. As with the chest press, the aim of this
exercise is not to move the horse, but to encourage him to activate his muscles
to keep his balance and resist the movement.

Rounding with a lifted hoof.

Balance exercise, pushing
on the shoulder with a lifted hind leg.

Strength

For further strengthening work of the core muscles, you could look to sternal lifts and “butt tucks”.

If you run your hand, pressing quite hard, along the sternal ridge that is the central line running underneath the horse between his forelegs, past the girth, and back towards the back of his stomach, you should see the corresponding parts of his back lift as he tightens his core muscles. In a less toned horse the difference is less obvious you should be able to see some effort from any horse. The amount of pressure required varies, particularly the first time whilst he works out what you’re on about. You’ll know when you have it right. On some horses it can be easier to use the blunt end of a
hoof pick rather than fingers to increase the targeted pressure to start with. Rest
assured that you are not hurting the horse, particularly if he hasn’t yet
responding by moving away from the pressure.

Activating the sublumbar and abdominal muscles to tuck the hind end under is an excellent strengthening exercise but can take a bit of trial and error. Stroke up the spine from the top of the tail with your thumb until the horse lifts his back, engaging his hindquarters. In an advanced horse you (and a friend) can do this at this same time as lateral bending and/or the thoracic lift. As with the previous exercise, you will be able to spot a
reaction when you get it.

In the very strong advanced horse you can combine these exercises with the balance exercises above, by lifting a hoof or adding a backward push.

Thoracic lift

Your horse may look at you with great confusion when you
start doing all these exercises, but they usually figure out what is required
fairly quickly. I find that in my horses, once they’ve tried the exercises and
come to associate them with treats, they are very enthusiastic about them. Mine
even occasionally offer an unprompted stretch in the hope of winning a prize.
You may also find that as your horse gets more experienced you can then do
several stretches to the reward, rather than having to load up on so many carrots
or pieces of his dinner.

I’ll post a photo series with more detailed guidance on groundwork exercises for people who are interested soon. I’m waiting for a magazine article or two (by me) to come out first so that I don’t scoop myself. In Part 3 I’ll cover ridden exercises, asymmetry and cavaletti.

Photography: Abby Cook Photography, copyrighted to Sian
Townson.

August 21, 2015
Today I’ve been sorting through old photos and came across these microscope shots of grass from a nutrition internship I did (in 1999) at the Roslin Institute, part of the Edinburgh Royal Dick Vet School and home of Dolly the Sheep. The superman-logo shaped ovals are stoma, but the dog-bone and four-leafed clover shapes are

Phytoliths – tiny lumps of silica, the same substance that forms the basis of sand and glass. This is what horse’s teeth are evolved to combat, the reason they need to be long. When the tooth’s surface is ground down new tooth can take it’s place, but without this sandpaper teeth will continue to “grow”, and gain sharp edges. Being tough lumps the phytoliths survive into hay, but aren’t present in pellets, hard feed, or some low calorie options. There are lots of reasons that horses need access to grass and/or hay, but dental health seems to be one that’s often overlooked.

July 25, 2015
Hobo update: can the mighty have fallen?

An update on Hobo, since my last piece on my grieving over him. I know that many are waiting for the next biomechanics piece, but right now all I really think about is Hobo. In truth my boy did not cope with retirement and neither did I. He was bored, angry, frustrated, and causing a lot of trouble in the field. So in March I began the painstaking process of bringing him back into work and trying to keep him sound or at least produce either a lameness that was manageable and still allowed him some stimulation, or a prognosis so clear that a tough decision could be made.

I brought him back into work thinking I was signing his death warrant and to start with every time he shoved his head into the bridle I cried. However with a lot of work and obsessive monitoring he became sound, pretty much stayed sound, managed to return to hacking and a little jumping, and became a relaxed, happy horse once more. He was a little intermittent and I was very cautious, but underneath I allowed my little hopes to soar again. Out came my favourite phrase: nothing is difficult because the steps are so small. He attended a clinic in April (clip below), where Blyth Tait declared him “probably the best five year old in the country”. Hobo’s 12, but I didn’t correct him; everyone likes a compliment. He went back into the ring (video also below), just over little jumps, because subconsciously I’m still saving him for some glorious future. Excuse the videos’ brevity & quality, my cameraman is 11.

A couple of weeks later, in May, Hobo developed a serious hoof crack when the ground suddenly hardened and I was reluctant to push him in case an altered movement affected his ability to cope with everything else, so he was back on holiday. That break cost me 3 rugs and a fence, and his waistline ballooned dramatically in only a couple of months. He came back into work last week and we’ve had to switch from the fat girth to the ridiculous.

At the same time there was a lump. A little lump on his shoulder that had done nothing all his life began to grow in about February this year. Nobody likes lumps, and I certainly don’t like change. Whilst Hobo was already against the odds I pretty much ignored it, and pulled out my second favourite phrase: not the crocodile nearest the boat. A couple of different vets passed through, had a look and we all agreed to ignore it together. We ignored it for months but it didn’t go away. In defiance of my dismissal it has continued to grow, now rapidly. It’s on the shoulder of the leg that has caused all the trouble, the leg with the tight tendon, with the sore navicular bone, with the giant splint, with the serious hoof crack, and these things are not unrelated. Once one part of a linkage causes a limitation other parts must compensate and will eventually struggle or even break down, particularly in a horse that doesn’t do rest, even under sedation.

On Monday Hobo had his annual vaccination and a terrible reaction has made me worry that his immune system is already struggling. He and I have decided that we are ready. Tomorrow morning (Friday) he will go under the knife and we will see what is there, how long he has, and if there’s anything else that can be done.

https://instagram.com/explore/tags/themightyhobo/

June 25, 2015
The equine back: how do you keep your horse’s back healthy?

Part 1:

Kissing spines, straightness, and the equine back: how does the back work, and how do you keep it strong & healthy?

This series of posts covers the structure and function of the healthy and pathological equine back, how to detect soreness, recover from injury, and improve strength. The equine back is a massive topic, and one that research is only just starting to reveal. This is a dramatically under-researched area, but recently the field has moved forward so fast that we have been able to discount many theories that once seemed very credible. This can make life a little confusing, but at least we do now have some good evidence behind our understanding of the back.

First let’s get the basics down.

The back, like all musculo-skeletal structures, is made of hard tissue (bone and cartilage), and soft tissue (muscles, tendons, ligaments and connective tissue). If you like tendons you’ll love my last post (link here) but for now let’s start with the bone: the spinal column.

Anatomy: hard tissue

The spine is made up of vertebrae, and these little building blocks fit together like lego. They run from the head to tail and have different shapes according to their region: vertebrae can be cervical (neck), thoracic (with ribs on), lumbar (small of back, behind the saddle) and sacral (fused region running through pelvis) and coccygeal (tail). For now let’s ignore the coccygeal vertebrae of the tail. Trying to hold your spine stiffly enough to carry a rider is hard, most animals can’t, and with all that to cover your horse’s ability to swat flies is not the crocodile nearest the boat. The tail is not completely irrelevant and can give us clues, but let’s address those another day.

The number of vertebrae in any spinal region can vary, but the total number in the spine (without the tail) is pretty constant. Long backs are normally due to long vertebral bodies rather than having extra vertebrae. Each type of vertebra has a distinctive shape, although weird transitional vertebrae with characteristics of two adjoining areas are quite common. Each part of the spine is adapted for different functions and brings its own unique problems.

The spinal cord, a bundle of nerves carrying the messages from brain to body, runs down the spinal column through a line of holes called the vertebral arch. The arch is roomy compared to the cord so normal movement doesn’t compress it, even when the spine flexes and rotates the cord is protected in this bone-encased canal. You wouldn’t know it’s there unless you needed to block a nerve, but osteoarthritis or fractures can narrow the canal and crush the cord, leading to seemingly-unrelated neurological symptoms.

The nerves branch off the spinal cord and exit through holes called the Intervertebral foramina, along with blood vessels and various other things. Occasionally a second pair of holes, the lateral foramina carries nerves. These holes are created if the caudal arch calcifies to divide the foramina and pinches on the spinal nerves. This means that even spotting the existence of lateral foramina justifies looking for spinal impingement.

Rising out of the vertebrae like sharks’ fins are the dorsal spinous processes (DSPs, black arrows in above). There’s a change in inclination of the DSPs (Picture b, below), as their role changes from supporting the soft tissue pull of head, neck and forelimbs (Picture a) to supporting the hind legs (Picture c). DSPs normally have spaces between them and usually don’t come into contact with each other. In some cases on lateral x-rays the spinous process can look like they are overlapping, but even then they are often not actually touching as they are not quite in the same alignment – i.e. in an side-on X-ray they look like they overlap, but in fact are out of plane i.e. one is to the left of the next, and neither is in the central sagittal plane. Sometimes, however, there is contact, and remodelling, and even false joint formation. This is the dreaded kissing spines.

The vertebrae also have protuberances called articular facets, and these interlock, stabilising the spine and through their joints allow different movement at different regions. Thoracic regional mostly allows lateral bending and axial rotational, lumbosacral mostly about dorsoventral motion (rounding and hollowing). An incredible 83% of horses have asymmetrical facets, and yet we’re surprised if one rein is easier.

The final fins coming out the spine worth noting are transverse processes. These provide stabilisation for the spine and lever arms for muscle attachments. In horses these have their own joints between them but not at every vertebrae. The amount of these joints not only varies between horses but these too are asymmetrical, which is pretty weird and probably something you should think about. The only other mammal this variability is seen in is the rhinoceros, and no one ever tried to make a rhino into a symmetrical athlete. Intertransverse ankylosis, a sort of arthritis in these joints, is really common, found in 50% of horses. It’s not clear whether this actually causes back pain. Watch this space, and we’ll see how the research pans out on this one.

The sacrum is made of five vertebrae that fuse at around the age of five years, and two centres of ossification (growth plates) that also fuse at 5.5 and 5 years, give or take 1.5 years. The sacroiliac joint is where the vertebral column articulates with the pelvis, and where the push from the hindlimbs is communicated to the spine. It’s a specialised shape to cope with transferring this much load – most moving joints have interlocking shapes that help hold them together but this joint is made up of flat surfaces held together entirely by very strong ligaments, and yet is a key site of flexion/extension in athletic function. As a result this is a common site of problems and pain, with degeneration often undiagnosed until post-mortem. In the pictures below of Sox jumping, the sacroiliac extension then flexion is seen, just behind the numnah.

Growth plates in the pelvis fuse around 5.8 years. By around I mean again +/-1.5years, and give or take 1.5 years is a lot of variation. When we give a 1.5 year standard deviation (+/-1.5years) this means that a 4 year old horse may already have completed this growth, and equally a 7.5 year old horse that had not would still be in the normal range. Tuber sacrale and tuber coxae are the highest and widest points of the pelvis respectively, and also the last to fuse. This means that they can suffer a little of knocked in the young horse. Otherwise, contrary to popular belief, I wouldn’t lose sleep over unfused bones.

Disc problems such as slipped discs are common in humans and dogs but not horses, who only have a small amount of disc material between each vertebrae, and a relatively immobile spine. Very occasionally disc degeneration is seen, but almost never herniation (slipped discs).

Conformation

A flatter pelvis has been associated with improved soundness (trotters), and improved performance (showjumpers and dressage) and yet a less flat pelvis (higher L5 angle) is linked to a higher range of motion and tendency to flex and extend this region more. Using a greater degree of motion in the region seems to push the supporting structures to the limit and cause more injuries. Other conformational aspects such as length and curvature of back contribute to the amount of motion, and so risk of injury. The vertebrae are interlocking and any relative movement causes a strain on the structures.

Soft tissue

The movement and support of the back is achieved by many layers of muscles, and there are many ways to group them. The muscles of the vertebral column can be divided into those running next to the spine (juxtavertebral muscles) and those nearer the surface (paravertebral muscles). The juxtavertebral muscles or intrinsic back muscles connecting the vertebrae provide support, stabilisation and motor control. These muscles have a lot of innervation so give the proprioceptive feedback that keeps track of spinal position and motion. The paravertebral muscles are larger, less innervated and provide gymnastic motion – flexion, rotation and lateral motion of the spine. The interlocking of the vertebrae means that the spine doesn’t really have the ability to bend laterally without also rotating, so these movements require the entire spine, and very little bending at any one single joint.

The spine is supported by the muscles that run along and above it (extensors), and the ventral muscles running beneath it (flexors) including the abdominal muscles and the sublumbar muscles (iliopsoas muscles). By finding an equilibrium between the two sets of muscles the horse is able to move efficiently by holding the spine in enough tension to support a rider and transfer power from the limbs.

Factors contributing to injury: carrying a rider

Carrying a rider’s weight can lead to many spinal lesions including impingement of the spinal processes and arthritis of the facet joints. Carrying an uneven rider and trying to do sports can add muscle strain to these.

Walk, trot and canter require a lot of passive movement from the spine, with the muscles mostly act in a restraining fashion. As the limbs move the spine extends and twists most at the points of common pathology. The precise spinal movement varies a lot between horses (large interhorse variability), but is very consistent in any one individual (intrahorse). Extension and twisting are particularly seen in diagonal support at trot and canter, where strong hip extensor muscles and abdominal muscles are essential to restrain the movement and avoiding strain on spine from movement.

When a horse takes a rider the weight of the rider naturally hollows the horse’s back, putting it under threat of damage such as spinal impingement. Muscular effort is needed to round the back and to stabilize it in this position, making it more able to carry the rider’s weight, to step under with the hind legs, and to transfer the push from the hind legs effectively. To achieve this the horse needs a large amount of muscle tone. For example abdominal and short back muscles are also particularly important for stabilising the back to allow propulsion from the hindlegs for collected movements, flying changes, and jump take off. In dressage horses pectoral muscles control the descent of the forelimb during extension – and can become overstretched and damaged if extension is not controlled. Similarly as the horse has no collar bone, movement at the shoulder, including bending or landing, requires a stabilized spine for the shoulder muscles to anchor to. The muscles of the shoulder are particularly common but overlooked sites of injury in the showjumper – taking the brunt of the landing by supporting the trunk in a sling of muscle between the forelimbs. The same shoulder muscles, particularly the trapezius and rhomboid muscles, can be common sites of anxiety related tension. The jumping pictures are of Sox an outwardly calm but inwardly worried showjumper, with me his slightly podgy, unbalanced rider. His trapezius gives him a lot of trouble.

Reducing the risk of and recovering from injury

Symptoms of back-related problems can vary from none to dramatic. The majority of horses with back pain show only poor performance and many sacroiliac problems are only diagnosed post-mortem. Horses might show “behavioural problems” such as rearing, bucking or avoiding the saddle or rider in the case of kissing spines, and restricted range of motion in the case of arthritis or muscle lesions, muscle wastage or hind limb plaiting in the case of sacroiliac pain, etc. Quite often back problems get missed, just because the symptoms are so diverse. Even when a back issue is suspected it can be hugely complex to diagnose.

During episodes of back pain the multifidus muscles, running along the spine, are selectively affected, and lose symmetry and size. Even after pain resolves, they do not naturally return to their previous size without intervention. This is turns increases the trouble that the horse is having, as they are no longer able to support the problematic area effectively. It is entirely possible that the cycle starts with localised wasting of one muscle, which then fails to stabilize the spine effectively causing back pain, which in turn leads to muscle spasm, shortening and disuse. In humans performing exercises to strengthen these muscles reduces long term recurrence of back pain, and it’s been shown to that strengthening the muscles that move and stabilize the spine has similar effects in horses.

Research has suggested that there’s benefit in starting core exercises of these spinal support muscles – of the spine abdomen and back – before the start of ridden work, and continuing them throughout the horse’s career, in particular during lay off or after injury. Many back injuries occur as the horse has no means of communicating a minor injury or stiffness, whereas a human with lower back pain would be allowed to rest. Jean-Marie Denoix is fond of saying both “engagement is the only way of exercising a horse without making it suffer” and “no abdominals, no back”.

Core mobilization exercises in horses include the exercises commonly referred to as carrot stretches – asking the horse to reach forward, down, and to his side using a target such as a carrot. On first inspection these stretches don’t appear to do much and hence these were much derided when introduced as ways to increase suppleness and relieve boredom in the stabled horse. However over the last few years research shows that these exercises require the horse to use his spinal muscles to maintain his balance whilst he holds each new position and so both strengthen these muscles and correct asymmetry. As such they are some of the most important tools in the rider kit. To start with the horse is asked to reach his head to his chest, between his knees, to his elbow, and to his stifle. These stretches target different muscle groups and open up different facets of the spine. In other cases a hand pressed on the sternum, side or rump of the horse as resistance can encourage muscle use. I’ll cover exercises and mobilisation in more detail in the next post.

Mobilisation exercises can be combined with work on a slope to develop strength and suppleness through the back. This is not necessarily the aerobic fitness work of cantering up hills, but for example a slow deliberate trot on a 20m circle, ideally the lunge or with a standing rider so that the back is free, using both the slope up and down hill, and even poles to encourage cadence and rhythm. The horse’s topline needs to be extended, nose lowered. Side reins aren’t going to help, although a chambon can encourage stretching and understanding. This is the type of exercise that when used twice a week can show a great improvement in horses with weak or damaged backs. As with all strengthening work, little and often is the most useful approach.

Back problems can come from a variety of causes – lack of warm-up, rushing the undeveloped horse to attempt activities or movements too early, asymmetry in the rider, “natural” asymmetry in the horse, tweaks during activity that aren’t allowed to rest. Problems in the limbs frequently lead to problems in the back, as any woman that has tried to walk in heels will tell you. The difference is that in horses we need to spot and correct these problems through our own vigilance.

Part 2 and Part 3 will cover the back musculature, function and dysfunction in more detail, detecting muscle soreness or weakness, the effect of training aids and discuss how to apply hill work, exercises, stretches, therapy and massage. Please note that this site constitutes discussion of athletic development and performance, and does not give clinical advice.

Some pictures adapted from Henson, 2013

June 1, 2015
Polar Bears: Four Legs Good, Two Legs Bad*

*Extract from a longer chapter on comparative locomotion. This post contains no horses.

The first polar bear I encountered
was in the Anatomy Department of the Bristol Veterinary School, and he was
already dead. Bears mark a point close to our hearts in the evolutionary tree –
being capable of both two-legged (bipedal) and four-legged (quadrupedal)
locomotion, but most impressively being able to casually choose between the
two. Polar bears don’t just use an upright stance to reach up a tree or get a
better angle on an anthill; they can stand and walk upright any time they want
to look a little taller or see a little further. They manage this with a
specialised spine and pelvis, and that is what makes them exciting to anatomy
departments.

Bear skeletons on the whole are so
similar to human skeletons that the first forensics lecturer I met at Bristol
claimed to have moved there from North America partly because he could not face
being called out to another “crime site body” that was actually a bear skeleton
with not a single bone of human remains. There are enough subtle differences
between human and bear skeletons though, that bears can achieve high speeds
using four legs, on land or in water, and we can only watch. The polar bear is so
good in water it is almost amphibious. There are some disadvantages to
this adaptability, as they had learnt in Bristol.

The Bristol polar bear skeleton
(pictured) had a name, Nina, and a friend, Misha, and both bears had come from
Bristol Zoo. Nina was imported into Bristol Zoo to partner Sebastian, a polar
bear who was born there. When Sebastian passed away in the 80s yet another
bear, Misha, was imported to keep Nina company. People don’t like to see
lonely animals.

Misha had spent her life as a
circus bear and arrived with a habit of pacing forward and back and nodding.
Whilst the zoo enclosure represented some seriously improved conditions for this
previously-caged bear, polar bears were already controversial zoo exhibits. The
general public had and still have a natural concern for animal welfare and so
it was considered necessary to keep Misha and her weird movements away from the
public gaze. By 1992 both bears had reached a remarkable age but Misha’s pacing
had grown more pronounced, accompanied by an even more exaggerated head waving.
The attempt to rehabilitate her was sadly exhausted at this point and she was
put down. Within six months, Nina the remaining bear had also began to pace,
and the decision was made that it would be kindest if she too was quietly put
to sleep. Both skeletons were sent to Bristol University Veterinary School for
post-mortem, and there it was discovered that these marvellous spines that
allowed these bears to do so many things also suffered from arthritis.
The very balance of
stability and motion that gave the bears options also caused their spines to
degenerate, and the bears had been stiffening up and becoming less able to
enjoy a full range of motion. In order to stop their spines from seizing up
altogether the bears seemed to have developed a series of exercises and
stretches – pacing up and down, waving their heads, putting their spines
through their paces and keeping the motion alive. It was this, the imperative
to stay mobile, and not the mental distress suspected, that eventually saw the
bears destroyed.

For all their popularity and
charisma when not caged, polar bears are rather dangerous to work with. They
belong to that special selection of creatures which, even when captive, are too
fluffy to put in front of a blue screen in film making. If you use a blue or
green screen with a polar bear you end up with brilliant action footage of what
looks like a completely shaved bear, when the fine hairs fail to be captured.
As a result polar bears have a skeleton and motion that is frequently recreated
using CGI for visual effects film work. It was wearing this hat that I
encountered my next bear, this time very much alive and called Mercedes.

I met Mercedes in Edinburgh zoo
but unlike Nina and Misha she had been born in the wild. Mercedes came from
the Hudson Bay region of Manitoba, Canada, where she could have lived out the
rest of her life if she had just stayed away from the humans. The Hudson Bay
contains Churchill, which is one of the most bear-prone towns in the world sitting
neatly between polar bear breeding and feeding grounds. Here polar bears get a
three strike rule. If a polar bear wanders into town and disturbs the peace or
generally endangers people it is tranquilized, captured, and labelled with
spray paint before being released away from inhabited areas. These labels mean
that a bear that is a repeated offender is easily recognised and our bear was
labelled dangerous bear number 39. On the third offence the usual course of
action is for the animal to be shot, but in our bear’s case once she had raided
town a third time a local car firm took up the case and offered to pay to have
the polar bear flown to a zoo or place of safety. The bear took on the name of
his benefactor and saviour, but finding a zoo prepared to take a polar bear was
not that simple, even once the search was extended internationally.

Bears may be
unwanted in suburbia, but another place that polar bears really aren’t popular is the zoo. For all the
reasons that Bristol struggled, most zoos will just not rehome a bear. They are
massively expensive to keep, the sizable enclosures are a substantial
investment, and the public just do not like to see them in captivity. Zoo after
zoo declined to help, until Edinburgh offered to take on the bear. Almost immediately
Edinburgh started to struggle with public perceptions – the bear was dirty, was
the bear meant to be dirty (yes), could the bear cope without company (yes),
did the bear have enough space? No captive polar bear could ever have as much
space as a natural territory, so psychologically, no, but Mercedes was getting
enough stimulation to keep her musculo-skeletal system in working order, yes,
and as alternatives go she also wasn’t dead. The public worried that the bear
looked sad and lonely and, as with Bristol, a mate was found. Polar bears are
naturally quite solitary animals and Mercedes hated Barney. The pair successfully
produced two cubs but keepers reported a great improvement to Mercedes’ health
and mental well-being once Barney finally passed away, having accidentally
choked to death on a child’s toy dropped into the enclosure.

The bear’s captivity continued to attract
criticism from the public and in particular their plight attracted violent
threats from the Animal Liberation Front, who started to attack and threaten
the keepers and all those associated with Edinburgh Zoo. Eventually a beautiful
territory was established for Mercedes in the purpose-built Highland Wildlife
Park, and despite concerns about how well she could re-adapt to the larger space
in her old age, she moved in in 2009. By this stage she had reached her
thirties, an age not usually seen in the wild, and like the Bristol bears
struggled as osteoarthritis slowly claimed her mobility. Another bear was taken
on, a two year-old needing to relocate from Holland to keep him a safe distance
from impending cub arrival. Luckily this time lessons had been learnt and
procedures were in place to allow the two bears to stay apart. In 2011, shortly
after her move, Mercedes’ arthritis reached the point where her movements
become strange, repetitive and “indicative of mental deterioration” and the
bear had to be put down.

Arthritis is also
seen in humans, including spinal arthritis. By making the commitment to
bipedalism, or two legs, we’ve sacrificed mobility for stability. Our pelvis is
fully rotated for our upright stance and so supports our more curved spine
better in that position, but the system still fails. Other bears, despite their
long hibernation patterns, do not deteriorate with age and disuse as polar
bears and humans do.

Happily the
similarities don’t end with arthritis. Like humans, ancient mammals, crocodiles
and hedgehogs, polar bears are plantigrade, meaning that they walk on the soles
of their flat feet. This is the primitive unevolved foot position for walking –
with animals that are more specialised for fast locomotion going on to develop
toe-running (digitigrade) and even toenail/hoof running (unguligrade). Landing
on your heels like a polar bear produces a lumbering gait – great for
stability, giving you more support on ice and if you need to balance on just
the two legs, but not so good for speed or shock absorption. Those huge, heavy feet
are never going to swing as rapidly as the hooves of the animals that evolved
to bounce along on the tips of their toes. The polar bear’s feet have some of
the largest, heaviest claws seen on bears and even have fur on, both handy for
ice-grip. Their paws are also webbed, and in water the shuffling gait becomes
an effective but rather cute doggie paddle. At 6mph it’s also speedy and manoeuvrable
enough to be not so cute when chasing you.

In return for all
this extra size and weight, the polar bear gains not speed but power. Humans
have a pair of bones in each forearm, and the same in their legs. Most species
have lost these extra bones and just use the one bone to connect elbow to
wrist, or ankle to knee, making them lighter, faster and more efficient. Polar
bears, like humans, have kept this paired arrangement intact, and keep all
their limb bones thick, dense and strong, and a result are impossibly
inefficient in their movement. Over short distances a polar bear can reach
35mph but it costs them, and this is the main reason that now that the ice is
retreating you hear about polar bears starving to death – they use up a ridiculous
amount of energy just to move, and reduced sea ice requires more movement. In
the summer when the ice retreats altogether polar bears out hunting actually
have an embarrassing and potentially fatal problem with heat stroke. Their only
means of defence is to stay as still as possible, even at the expense of a
meal. The advantage of the double bones, particularly in the forearm, is the
extra anchoring point for muscles which gives polar bear’s limbs the dexterity
to rotate. This makes the polar bear an impressive all-terrain traveller, and
when combined with their short, stocky, limb-bone structure you have a powerful
animal perfectly adapted to swim, dig, and hunt. Just not to run. These ice
bears do not just need a bigger enclosure, they need ice.

May 28, 2015
Tendon training, age and maturity. How do your horse’s tendons become stronger? How can you give the best start to your foal?

My last post covered a little about tendon structure, hysteresis and crimp and what all this means for the equine digital flexor tendons (link here). This time I’m going a little deeper into how tendons work, tendon creep, and how to make tendons (and ligaments) stronger. The main tissues I’m going to talk about are the superficial digital flexor tendon (SDFT), deep digital flexor tendon (DDFT), and the suspensory ligament or third interosseous muscle

(SL), which despite its confused names is usually classed as a tendon. These form the suspensory apparatus, and I’ve talked a bit about what they do in the last post, but I’ve put a picture above so that we’re all on the same page (from one of my previous papers Lawson et al., 2007). The picture also has the main bones of the distal limb marked – the third metacarpal (MC3), proximal sesamoid bone (PSB), distal sesamoid bone (DSB), P1, P2 and P3.

Tendons are made up of a lot of different proteins, but the two main ones are collagen which resists loads and elastin which allows stretching. In tendons the collagen fibres are mostly parallel. This makes them effective in resisting forces from one predictable direction, and in turn being exposed to unidirectional forces encourages fibres to align and be more parallel, and we have a happy cycle. The collagen fibres in ligaments are less organised, as they can be pulled from more than one direction (see picture below of my lovely collateral ligament model). This makes ligaments weaker if we’re comparing stretching in one direction. In tendons and ligaments, collagen fibres are crimped when not under load, so they have an increased ability to lengthen and resist force without failing when they’re aligned in the right direction, more about that in the earlier post.

The amount a tissue can stretch compared to its original length is measured using strain (the ratio of new length to original length). The other thing we’re fond of measuring is stress, which is the load it’s exposed to as a proportion of its size (force per area). The amount a tissue will deform for any given load (stress divided by strain) is called the modulus of elasticity. This varies between tendons, and is one of the properties that will determine ultimate strength. The stress vs strain graph pictured shows the effect of modulus of elasticity on point of failure (ultimate tensile strength). The more a tendon can lengthen, the more load it can take before it fails.

So as tendons are not equally strong in all directions (anisotropic),

the chance of them failing partly depends on the direction of the force and partly on the tendon’s (modulus of) elasticity. The final important factor is how quickly a force is applied (viscoelastic properties).

Creep is the effect that allows tendons to progressively lengthen under the same force which has the effect of releasing tension. It’s the reason you can get further if you hold a stretch and keep stretching. Does it matter? Well, it means that tendons are great with constant pull, lousy with sudden impact. This is the reason that I talk a lot about the initial impact spike of hoof hits ground, and its effect on the digital flexor tendons, despite the fact that peak tendon strain occurs in mid-stance (for SDFT and SL) or end-stance (DDFT). Sudden changes in length such as a tendon struck (and stretched) by a hoof or an unexpected footfall from uneven ground – whether that’s rabbit holes or inconsistent arena surfaces, this is what causes a lot of injuries. I have a deep resentment of inconsistent/patchy all-weather surfaces.

To try and understand how to develop stronger tendons, a lot of research has compared foals raised in stables and given different formal exercise regimes with those kept in fields. Pasture-kept foals, that live out 24/7, consistently grow stronger tendons not just in the short term but actually develop tendons with more collagen fibres – i.e. with a higher potential strength that they can achieve through training. Whilst increasing exercise in stable-kept foals does lead to stronger tendons, in all studies 24/7 pasture exercise induces more strengthening changes than controlled exercise combined with stabling. Foals that are shifted from box-kept to being field-kept will to some extent catch up, but are unlikely to ever reach the same extent of collagen structure and tenocyte metabolism as foals that have always been in the field. It’s worth mentioning that in research tests horses that live in but have access to 2-4 hours of field time a day are considered to be stable-confined. You just can’t get the same amount of stimulation in 3 hours as you can in 24. Similarly pasture-kept horses are rarely in “natural” conditions, as pasture-size and herd-size tends to be limited, which reduces the amount of movement horses experience. You get the picture.

Research looking at the effect of training on tendons of horses of different ages supports this. Contrary to popular belief early training whilst immature can reduce the risk of injury in the older horse, as younger tendon has a strong ability to adapt to exercise and older (mature) tendon less so. The equine digital extensor tendons do grow (hypertrophy) with sprint exercise, but not so much the flexor tendons. The SDFT and SL, with their role in elastic energy storage, do not appear to gain in collagen content or diameter with exercise once fully mature, and these tendons are mature by the time the horse reaches about two years old.

After maturity tendons get weaker with age, and so become more likely to fail at a lower strain rate. When the horse is 5 years old the SDFT has already started to degenerate, with changes in crimp angle and collagen levels causing a reduced total strength. From here on in exercise accelerates this age-related degeneration.

Some studies have shown exercise-induced increases in SDFT diameter in 2yo thoroughbreds (but not warmbloods), but not an improvement in crimp angles or biomechanical properties – in other words tendons got bigger but not stronger. Tendons can grow due to pathological changes, so in research studies an attempt is usually made to rule these out by biopsy or ultrasound (as it was in this case). Tendon can also increase in volume just due to gains in water content, which is an exercise-induced response, but not one that helps. In immature warmbloods, all tendons and ligaments adapt, improve and strengthen in response to exercise, all apart from the SDFT. In all horses the SDFT just behaves a little differently.

In elastic-energy storing tendons such as the SDFT, increased size

increases stiffness so an increase in size actually reduces function. In these tendons being able to lengthen elastically rather than snap is more important, and so too much stiffness is dangerous. The improvement in the common digital extensor tendon with exercise is more helpful in improving the performance of the SDFT as these two tendons work together to help the SDFT hit the right stiffness for elastic-energy storage from hoof strike to push off. As I covered in the last post, the introduction of scar tissue in the tendon from overuse or previous injury is another potential source of increased stiffness.

Compared to hugely-responsive tissues like bone, tendon adapts slowly to exercise, and possibly not at all once mature. It may be that research in this area just isn’t precise enough at the moment to detect changes and predict optimal training regimes. In the great hierarchy of research funding, grants are keenly fought over and some excellent projects will always go unfunded. Understanding equine tendons is not the crocodile nearest the boat for many funding bodies, and not all human research can be directly translated as equine tendons are so unique. Research continues; slowly.

Images from my own research and graphs as before from Robi et al. 2013.

May 24, 2015
Tendon biomechanics, equine digital flexor tendons, and crimp. How does all that work then?

When I first studied anatomy I was told that tendons had a very specific job – they attach muscle to bone, and so transmit the force of the muscle pulling to the bone, often creating movement at a joint. Ligaments, I was told, attach bone to bone and create stability at joints, holding it all together. However in horses there are some special cases where the tendons start at a bone, travel a long way and then have accessory ligaments anchoring them back to another bone; only part of the tendon is actually attached to any muscle at all. Anatomists can get very excited about which structures are tendons and which are ligaments, but we can agree that sometimes tendons have other jobs, and the muscle is just there to help adjust their tension.

Long tendons are part of what make a horse so interesting to study, and one of the ways in which the horse is specialised for locomotion. Horses don’t walk on flat feet like humans, they walk on their toenails. The muscles that control their legs are placed right at the top of the limbs, leaving the lower or distal parts to be lightweight, fast, and full of shock-absorbing joints and long tendons to store and release elastic energy. The digital flexor tendons of a horse are familiar to most horse owners because they include the most common sites of injury, as they take the brunt of impact and are predominantly stretched by the movement of the joints rather than tension in the muscles. These tendons are not there to transmit muscle pull and cause movement, they’re there to absorb motion, stretch like a rubber band as the hoof hits the ground and then ping back to length as the heel comes off, pulling the leg along with them.

In humans most tendons are short, strong and transmit force by acting like a rope. In horses’ legs these tendons are longer and more elastic. The digital flexor tendons and suspensory ligament run down the back of the horses’ legs. A sesamoid bone at the fetlock acts as a pivot and allows the tendon to transmit tension smoothly around the joint. As the hoof hits the ground, usually with enough force to break the cannon bone, the joints of the leg flex, and only the hoof feels the full brunt of the impact. The hoof travels fast and when it hits the ground it stops suddenly. Ideally the surface allows some slipping, but if the horse is wearing studs then the hoof stops very suddenly indeed. This deceleration causes an impact force. Flexing of the joint above the hoof (distal interphalangeal joint) allows the pastern bones (medial & proximal phalanx) to decelerate more slowly and flexing at the fetlock allows the cannon bone (metacarpal bone) to decelerate more slowly still, so these bones experience less impact. As the joints flex they stretch the digital flexor tendons, storing elastic energy. As soon as the heel leaves the ground the superficial digital flexor tendon can start to spring back to its shorter length, releasing this elastic energy, and helping the leg bounce along in very efficient way. Similarly the deep digital flexor tendon will recoil at toe off and return to its former length.

Except sometimes they don’t. Tendons need to be springy and elastic, but not stretch so far that they fail. One of the ways they do this is by not being straight: their collagen fibrils form a tight wave pattern – they are literally crimped. Tendon crimp means that whilst the tendon is never slack its initial bit of stretching just involves straightening out – the toe region of a length force graph. The more pronounced the crimping, the more force and stretch a tendon can take before it fails. Similarly as the horse warms up its tendons “become more able to” straighten out ready for work and are capable of sustaining larger forces and longer stretches without failure. Generally tendons are expected to work within this toe or linear region. Even within the elastic region that the tendon is capable of working in, not all the elastic energy is returned and some of it is lost as heat (hysteresis, shaded in pic). Heat build up in tendons is another major cause of damage and the reason that many old fashioned brushing boots have become unpopular.

Lesions and microtrauma in the tendon show up as imperfections in the crimp pattern, making it irregular, disturbed or with less crimp angle. These range from micro-lesions to full on blown tendons leaving big lumps of scar tissue, and as you’d imagine they all affect the tendons ability to stretch. Micro-lesions are built up by pushing the tendon to the point where individual fibres start to fail, and if not allowed to recover eventually these may cause complete failure of the tissue. The majority of catastrophic failures though require some external influence to push the length beyond the limits – such as an over-reaching hoof kicking into the tendon whilst it is already stretched.

With use tendons become stronger, more elastic, with their fibres better aligned. Basically they can withstand more before they fail. However with overuse or just plain ageing damage makes tendons weaker. The trick then, is to give a tendon plenty of training within its current elastic capabilities. Training actually affects different tendons in different ways, and responses to age-related degeneration and exercise are actually very different between for example the common digital extensor tendon and the superficial digital flexor tendon in the same leg of the same horse. Similarly there is a certain limit in how strong and elastic any given tendon will develop, based on getting the magic optimum amount of exercise in the foal. These posts sit on my desk unfinished for a long time if I try to include too much in them, so let’s stop there and cover those topics next.

Images courtesy of Jean-Marie Denoix, Ecole National Veterinaire d’Alfort, and from Robi et al., in Hamlin et al., 2013, with thanks.

May 4, 2015
Riding confidence: decision making and problem solving

I used to admire the way that some riders could just get on any horse, and have it go well for them. When I was little I thought that the sign of a truly experienced rider was being able to hop on any type of horse and play a tune. So I went out and I rode as many horses as I could, and I grew better at riding new horses by matching them to a previous one. “Ah, this one goes like the spooky thoroughbred, I have to encourage his back to loosen with my light seat”; “ah this one is like the little welsh, I have to motivate her to want to be forward”. The more horses I rode, the more my repertoire improved and I could understand each horse quicker and more easily. These days it seems a little different to me: now I believe that a truly experienced rider can switch “between horses” even during a ride, whilst still on the same horse. Sometimes the horse is onward bound and spooky, and sometimes he is backing off and behind the leg. You can’t always ride the same horse in the same way. I have to speed up my understanding to not just change my riding from horse to horse but minute to minute, second to second.

I tell undergraduate university students that there is no right or wrong answer. Whether I agree or disagree with your point rests on how good your argument is. The marks don’t depend on writing down what I already have in mind, the marks depend on providing a concise, logical, referenced argument. Luckily at undergrad level I also mark the exams, so I know that this is true. At school age sadly there is a right answer, because our school system is an abomination, but that’s a different article (and Michael Rosen already nailed it: https://t.co/j3p3zEpFy4).

So what about riding a horse? Recently I had a horse who behaved in defiance of clinical diagnosis. I sat with my vet consult and worried that the horse didn’t match expectations but the vet just said “Horse hasn’t read the textbook.” It’s a phrase I now use a lot. You can expect all you like, but he hasn’t read the textbook. If you ride, then you just have to ride the horse you’ve got on the day you’re on. You can remember to keep that pesky bad habit at bay, to be more tactful or more positive, but that combination of your horse and your day is unique. That moment is unique: you might have walked the jumping distance on six strides but then you clambered over the first part and this is when you need to react. This is no longer a six, this is a hold for seven. You might have an engaged, forward dressage horse that you merely need to release to extend, but right now he’s worried about those flowers and you’re going to need a lot more leg.

Riding is an education and it’s more like university than school. There’s no right answer but the thought process is important and takes intelligence, it’s logic and reaction and sometimes research. Decision making is a skill, like any other riding skill, and something that you need to practise. People that feel nervous are often mostly worried about the what ifs, specifically what if I make a mess of it, what if it goes wrong, what if I get to the fence and there is no stride. Problem solving skills don’t just help you out of a mess, they make you feel more confident that it won’t arise. There’s no point being able to shorten and lengthen to a fence if you don’t have the reactions to know when to use which, so you also need to work on those reactions. I used to think experienced riders could see a stride and I had to learn this magic: how to see a stride. Now I realise that they just have a strong rhythmic canter and make decisions well. Similarly leaving an arena realising that he would have settled if you’d softened your inside hand is just too little too late.

So what’s the magic answer, how do we train creative decision making and problem solving skills? In equestrian coaching we tend to stick to drills: come down this distance in six strides, go from the ten metre circle to shoulder in. Drills are important because they build muscle and a skill set, but they can’t be everything. The opposite of this approach is a more game-based environment, you send someone around a course and they ride it as it comes, yes they start with a plan but they also have to react, and in doing it they practise reacting, and they build confidence in their reactions – maybe they cut a corner and realise that that distance is now just going to work better on a five. To do this the rider needs to be autonomous, they need to have a voice and not just be directed by the coach.

Another thing that’s made it from the research to (other) sport coaching is the use of silence. Sometimes silence is as useful as feedback: try the distance, OK, that didn’t work, go back and try it again. No advice, you decide what to change. The coach needs to allow the rider to develop the skill of self-correction – to learn from their own mistakes and sometimes work out their own corrections. We’re fairly good at allowing horses to do this, but often struggle to apply it to the riders. Using silence as a coach is terrifying because you want to contribute, but sometimes stepping back is the most useful thing, still observing, still being there to lead the discussion after, but setting someone up to learn rather than telling them your answers. You can avoid leaving the rider feeling that they were merely told to “jump this, jump that” using feedback and discussion and summarising well, and sometimes this can come later. If more direction is needed the type of feedback can still be tuned to self-directed learning: “his shoulder is falling out” is more useful than “more outside hand”, better still is “is he straight?”

So is it just practise? Well, as with all riding it’s the right sort of practise. The nice thing about the example of jumping related distances or counting strides to hit a certain stride length is that you know when you’ve done it well, even if you don’t have a coach with you. You can tell when you made good decisions and when you need to come again. Some days I’m so busy trying to breath correctly, keep my hips straight, my seat light and my shoulders up, that I’m too focussed on my own body. This is the death of good intuitive decision making and my stride counting becomes “1, 2, many”. If I want to practise my ability to shorten or to lengthen, or just to take an even stride, then stride counting matters. If I want to practise decision making then it doesn’t actually matter whether or not I know how many strides should be left, I just need to react to the stride pattern I’ve got and the distance in front of me. I don’t even need jumps – I do it with poles on the ground or on hacks between trees or distinctive pieces of grass. If I’m stuck as a passenger on a long car journey I even “jump” road signs. Do it in different places and it’s a different exercise because hacking through the woods horse is not the same as cantering across a field horse and yes, you learn what works in different situations but you also practise problem solving and making decisions.

I’ve used the example of stride patterns pretty consistently but to be honest this is true of a lot of exercises. Anything that you want your horse to do might require a reaction from you, and the more you create safe situations where you need to react flexibly, the more you can practise that skill set. Nothing builds confidence like knowing that whatever happens, you can probably deal with it.

April 13, 2015
Cognitive bias and the horse-owner

Let’s talk psychology. Not the horse’s, you, your messed up head. There are several ways in which humans are lovely but irrational, one of which is cognitive biases. They affect you every day, on or off a horse, in equestrian or any other sport. I find them generally fascinating and right now I’m avoiding doing something else, so here’s a simplistic introduction to some common ones:

Sunk Cost Fallacy, Loss Aversion & the Endowment Effect

Sunk cost fallacy is the reason people who have already wasted money on tickets to a terrible film also waste their evening watching it. Sadly it can also be the reason people eat terrible food, get married, or take any next step – it’s the urge to justify previous decisions using the next one, despite the fact that throwing good time/money/energy after bad will not result in a gain.

This can mess up your horse-life. It means that you always want to progress in one direction. I’ve taken 20 years of dressage lessons so I’d better stick to dressage. My horse was bought for jumping, so I’d better do that. I’ve tried to solve this issue this way, so I’d better carry on. Why? There is no refund. We have an ethereal idea of “money or time wasted” despite the fact that often no future course will get that time or money back. You are where you are today. Go forward, in any direction you choose. Your horse is not wasted, your horse does not care.

Similar to sunk cost fallacy, loss aversion worries about the past, but in this case it’s avoiding facing an actualised loss. We hate loses, we are more averse to loss than we are attracted to gains. It’s the reason that people can lose millions on the stock market – when stocks start to sink people don’t want to sell quickly and take the small loss. Your stock is worth whatever it is worth today. It doesn’t matter whether you bought it today or last month, no one cares how much you actually paid for it – holding on to it hoping the price will go back up is fine, but it’s no stronger a position than buying it today. You’ve already lost the money. Sell the damn horse. This also matters in a less financial sense: I’ve already taken the day off/ put the big jumps out/ planned this hack. Whatever. Sometimes you’re genuinely happier if you can just put down the stubborn and take the hit. This also applies to getting problems diagnosed. I’m looking at me here.

Loss aversion is thought to be the reason we have the endowment effect – a phenomenon where people want more money to sell something than they’d pay themselves. It’s worth more because it’s mine. You don’t need me to talk about that, you’ve all got horses.

Confirmation Bias, Selection Bias & Ignoring Probability.

Can you have a favourite cognitive bias? I love confirmation bias, I see it every day. Ever noticed if someone annoys you everything they do is annoying, but if you have a crush on them then everything about them is lovely? We love patterns, and are evolved to try and make sense of the world quickly by seeking them out. We also love to be right. This gives us confirmation bias, where once we’ve formed a theory we look for evidence to support it, and ignore evidence to the contrary. This doesn’t half help people sell miracle cures. Given 30 horses that the gadget/supplement doesn’t work on, we’ll notice the three where it does; even though their improvement was probably nothing to do with the gadget/supplement/lucky socks/lack of turnout the day before. This doesn’t mean we’re stupid, it means we’re mathematical modellers, and want to find the trend.

Selection bias is a very similar phenomenon. If I tell you to look out for a red car or the number three you’ll notice it everywhere. You’ll be sitting in a red car and suddenly notice that it’s 3.33. Is it because I’m made of magic? No, it’s because there are several million individually observable things that happen to you every day, you just don’t normally take any notice of most of them. Why should you? Given several million things that you could observe, you’re not going to imbue significance into every single one – one in a million shots happen all the time, three or four times a day. Guess what I just walked passed? A car with the number plate NG12 2GF! What are the chances of that? One in 456976000 (four hundred and fifty seven million)! Are we excited? No, we really, really don’t care. Unless you’re actually looking for that number plate, but you know the odds were the same either way, and I still passed it. If you’re testing the theory that your horse goes well after you saw an N, or a G, or a 2, then you’re all excited, but that that doesn’t make it a randomised controlled trial. Of course you can see things if you look for them – do you think I actually know where I keep my keys? Doesn’t mean there wasn’t also a mug in the room, but I wasn’t looking for that mug.

Your subconscious is innumerate, or at least rubbish with probability because you’re dealing with a lot of data and sometimes it summarises badly. Clustering illusion means that any random set of data looks like it has clusters of data points in it. If it didn’t have clusters of points, it wouldn’t be random scatter, it’d be an evenly spaced pattern. Our addiction to order makes those clusters very seductive, but just because two things have happened at the same time doesn’t make them related, just that we looked for a pattern and we saw one. Sure you have a training method that generally gives you great results, that’s not necessarily an illusion, you’re probably mentally collecting a lot of data on that, noticing all the little things that give you a fairly accurate idea of what’s going on. But your friend’s horse had a similar problem and it got better when they put a dandelion on it’s head? That is what I mean by snake oil. That way madness lies.

I covered gambler’s fallacy a little in the last post. If you throw two heads in a row what are the chance of landing heads again? Still 50%, the same as your chance of throwing a tail, because your coin doesn’t care whether you just rolled heads. The idea that it does, and that there’s such a thing as a “run of luck” or that the roulette wheel can be at any point “due” to land on black is the reason that slot machines are the most profitable part of any casino. This doesn’t mean that you can’t have good form – confidence begets confidence and if your horse is going well there’s no reason that that should change. Similarly, you’re not due a win, but if you keep performing well probability says that you might have one. Point being the harder you train the luckier you get. Isn’t it the Whitakers who like to say that you win at home, and just go to the show to collect the rosettes?

Functional Fixedness

Functional fixedness is the phenomenon which makes you spend an hour looking for a hammer, whilst holding a perfectly heavy spanner. People don’t think of hitting a nail with a spanner, because they’ve categorized it and so forget it can do other things. Horse riders are remarkable at overcoming this. It’s not just a martingale, it’s a neck strap. It’s not just a lunge rein, it’s a loading device. Yet we still come out with “he’s a showjumper”, “she’s a cob”. Don’t get me wrong, it’s great that he’s a showjumper and she’s a cob, unless you’re implying that that prevents a second career or even a different first one.

Dunning–Kruger Effect

Deep breath. Dunning-Kruger effect was described by Darwin as ignorance begets confidence. Brutally, the less you know, the more likely you are to perceive yourself as an expert, and the more you know the more likely you are to not realise your own competence. This means that a lot of unskilled/uneducated people have illusory superiority, and love to force opinions, and a lot of excellent riders can’t explain how they do things because they assume what’s easy or obvious to them is the same for you.

There’s so much for more to say but this is already long and I’m drifting into dangerous pet-hate territory. Suffice that cognitive biases are not just crazy. Having a few short-cuts helps us make fast decisions on millions of things, just sometimes we get carried away with that when in fact we’d be better off realising what our influences are and why we want to do something or not. Go forth, be rational, and be a little more understanding of those that aren’t.

March 11, 2015

Equine Mechanics

Insights and resources on equine biomechanics for horse owners, trainers, and enthusiasts.