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This article has two main purposes :-
Section 3 extends the approach to cover the four main gaits that the horse uses. As well as describing the patterns of leg movements involved in the gaits it attempts to put the use of the different gaits into a wider context including racehorse training regimes.
Section 4 defines an approach that we can use to get started when assessing athleticism. Therefore, a relatively simple framework is proposed that can be used to start to understand the impact of the complex factors involved. If we do not define the 'problem' and a method to make some progress then any discussion of 'athleticism' is going to be piecemeal and superficial at best.
The aim of the text is that it should be fairly easily understandable to someone with an interest in horse racing but without any background equine knowledge. Too many explanatory documents assume that the readers are already on a highish 'plateau of knowledge' and therefore will already understand a range of jargon and concepts. These are then used in the explanation and if you do not know them the effect is to leave you feeling you knew less than when you started reading the explanation. To extend the metaphor, if you are on the valley floor below the 'plateau', or lost in the forest on the slopes up to it (as most of us are) then hopefully this article will help progress and not hinder it. Soapbox away.
The next section will cover the horse's gaits and the leg movement sequences that they involve. It is common to use four or five side on pictures of horses at various points in a total stride cycle of to illustrate the gaits but this is rarely enough to enable someone to visualise the full stride sequence. It is useful to consider the simpler two legged examples and other methods of representing the stride pattern rather than just the pictures.
When a human walks both legs perform the same movement - they swing back and forth like a pair of pendulums on a pivot bar made up of the hips and the pelvis. They differ from a simple pendulum in that they are driven by muscles and they become an inverted pendulum when they hit the ground (now the pivot point) and the body is levered up-and-over on the leg.
However, let us keep it simple and concentrate on the back-and-forth motion. In the walk we will call the whole period between a foot hitting a ground and the same foot hitting next time a 'stride'. In a two-legged animal this then covers two steps - one with each foot. We should note that in humans we can also use stride to mean one step but with horse's the stride length means the whole cycle from a foot hitting the ground until it next does so we need to start out consistently.
In the walk the two legs complete the same back-forth motion but not at the same time. In fact they are doing the opposite of each other with one going backwards as the other comes forward. This brings us to the first feature which can be used identifies a gait. In a total stride (two steps in humans) how far offset from each other, in time, are the legs in the motion they trace out. If we define the duration taken to complete a stride as 1 then we can then identify the difference by which the two legs are displaced relative to each other. In a walk there are two legs doing the opposite motion during the period of time 1 and therefore the displacement is 1 (total time period) divided by 2 and the answer 0.5 (half a time period).
In Figure 1 below the first picture is a plan
view of a human walking with the '0' on the leading foot indicating this
is just touching down. The '0.5' on the trailing leg indicates it is half
a full stride cycle (i.e. one step) behind. To show how this is useful
in getting a handle on the actual movement look at the second picture on
the far side of the Figure. This represents a person who is jumping forward
in bounds. Here both feet have '0' next to them indicating that they are
not offset from each other at all, i.e. both legs are doing the same thing
at the same time and a single overall stride is one 'bound'.
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To identify a stride cycle fully we need information about one more feature as well as that about how the individual legs are offset in time from each other. This relates to at what times in the overall stride each foot is in contact with the ground ('stance phase of the stride cycle') and when it is in the air ('suspension phase'). The diagram in the middle in Figure 1 is an example of how this information can be displayed. It shows the pattern for a human walking with time increasing from left to right (in effect with the person walking in that direction).
Where the left foot is on the ground the upper bar is coloured blue and the lower bar is red when the right foot is on the ground. The diagram starts on the left with the left foot on the ground and the right having just taken off from it. As we move rightwards in the diagram and forward in time the right leg swings forward and hits the ground while the left foot is still in contact with it. The left foot then takes off an swings forward and so on. A vertical line drawn at any point on the diagram shows you which feet are on the ground at that time. For example we can tell from the relatively short overlap of the red and blue bars that this person is walking quickly and regularly (e.g. consider what the picture would look like for someone with a bad limp).
The diagram is also useful in highlighting another point about gaits and how speed of movement can increase. As the overlap of the red and blue bars decreases you reach a point where the person is walking as fast as they can. Assuming they are using their full leg length in reaching forward each step how can they go faster? The answer is to not have any overlap at all and have a fully airborne phase (no feet on the ground) between footfalls. We do this naturally, we change gaits from walking to running.
As part of the background the the discussion of athleticism later it is worth covering what structures are involved in movement. The four main ones are :-
To produce the full movements to produce any gait (walk, trot etc.) involves a very complex interaction of a large number of muscles. To simply move one foreleg back and forth requires ten major muscles working in an exact pattern and a number of lesser muscles. Which is why movement to a great extent is not under conscious control and is instead 'hard-wired'. The systems used to control the movements add another layer to what produces athleticism.
At this point it is worth considering an area that will be very familiar to anyone following horseracing - tendon and ligament injuries. This article was written in a period with regular news of contenders for the Cheltenham Festival being withdrawn with these problems. Where are these injuries and why are they so common? The answer to where they are is in the lower limbs (usually the foreleg), to explain the why? requires some background about the horse' leg structure.
One of the adaptations the horse has to make it a highly efficient athlete is that it has relatively long legs for its body size. However, evolving to have longer legs works best if they are light, especially at the 'ground' ends. Muscles are heavier than bone, tendons and ligaments so removing these from the ends of the legs will make them lighter, easier to swing back and forth and more efficient. Think of how quickly you can swing a baseball bat back and forth if you hold it by the lighter, handle end or by the hitting end. Alternatively think of how a long whip's 'crack' generated at the handle end becomes a much faster motion (the 'crack') at the lighter far end. How efficient would it be to try to produce the crack by holding the light, thin end?
So, the horse has made the most of increasing leg length by extending the structures at the bottom of the leg and controlling them with long tendons which stretch back up to muscles above the knee and hock. The 'knee' in the horse (the joint halfway down the front leg) is the same structure as the wrist in humans. The hock joint (halfway down the hind leg with a backward facing 'point') is the same as the ankle in humans and the backward 'point' is the same as our heel.
The horse has lengthened the bottom of the leg over time by extending the bones that make up the middle digit. If you look at your own middle finger the bones equate to the bones below the 'knee' in the horse. The hoof is what the fingernail becomes after a very long period of separate development. But there is another major difference. Looking at your middle finger again it has muscles right the way down to the end. We developed this way because dexterity and good grip were the qualities we needed. The horse remained a quadruped and weight carrying along with efficient, fast movement was what was required..
Which brings us back to injuries. The lower leg therefore has a set of unusually long tendons which run from above the knee (and hock in the hind leg) right down to the joints just above the hoof. Because there is no muscle mass these tendons have no physical protection from knocks and bumps (including hits from the hind hoofs in the case of those on the back of the forelegs). Added to this the tendons are stretched each time the leg lands and help to absorb the full impact of the horse's weight at high speed.
Which explains why tears and damage to the tendons in the lower leg are very common. When you see trainers feeling the bottom of legs they are looking for heat spots, or possibly physical damage, which would indicate an injury. Because the tendons are just below the skin they are easy to assess. A horse with a bad tendon injury may be off for a year a more with perhaps 6 months of rest and walking to allow the tendon to heal. The horse will then need to go through a progressive training regime to get its race fitness back.
The term 'getting a leg' used to refer specifically to the major tendon that ran down the back of the foreleg but is now used more widely to refer to any lower leg tendon problem. The suspensory ligament runs down the back of the leg and provides support to the main tendons there via links to other ligaments. Lower down the the leg it branches and links to the tendons at the front of the leg and therefore damage to it can cause a range of problems.
The following sub-sections describe the gaits of the horse uses using the diagram types covered above.
The are two gaits that the horse uses where there is no suspension phase and at least two legs always are in contact with the ground at all times - the walk and the pace. The majority of breeds of horse only use the walk and a small number of specialist breeds that pace.
Figure 2 below shows the hoof-fall sequence
for the walk and how the overall stride is split into four equal parts
with one leg landing after a quarter of the time. The front and back pairs
of legs are out of step with each other like a pair of soldiers marching
in line but with the second-in-line soldier starting out off the wrong
foot and slightly late. [If he started out on the wrong foot at the same
time they would be 'trotting' which the horse does not do without a suspension
phase].
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The term 'four beat gait' is used for the walk because there are four separate hoof-falls and they should be a regular rhythm. The feet should be lifted and placed cleanly and each pair of legs should be well matched. A horse which drags it's feet, rather than lifting them, is usually a negative sign.
Figure 3 below shows the pace gait for the horse but note that the thoroughbred does not use this gait. The pairs of legs on either side move together and is like two soldiers marching in step. This produces a two-beat rhythm with only two sets of of hoof-falls. The small number of specialist horse breeds that can use this gait tend to have been bred as 'trail horses' and used for long distance rides. Riding a horse with this two beat rhythm is more comfortable than the four beat rhythm over a long ride.
The other interesting point to note is that very
long legged animals like camels and giraffes cannot trot and therefore
use a fast version of the pace instead. Why not trot? Because their legs
are so long they have to work in unison on the same side, if the front
leg were coming back as the rear was coming forward they would clash.
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A brief recap - a stride is the whole movement involved between one of the horse's feet hitting the ground and the next time it does. The horse has four legs so to split the entire stride up evenly you either end up with quarters (i.e. the walk) or halves by pairing the legs up in some manner. Pairing them on the same side produces the pace gait, pairing them up front and rear produces the 'bound' gait which is how a rabbit moves but is not used by the horse.
The alternative is to pair the legs up diagonally
with the left front following the same movement, at the same time, as the
right rear and vice versa. Which is a description of the trot although
it can be summarised as the horse jumping from one diagonal pair to the
other. However, note the difference that the trot always includes parts
of the stride when the horse is airborne (all four feet off the ground).
Looking at Figure 4 below shows that there are two airborne
phases in each stride in trot, one for each 'jump' from a diagonal pair
of legs to the other. This produces a two-beat stride.
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The horse can trot at speeds above 30mph and close to 35mph for the best, purpose bred, trotting breeds. Although unfashionable in Britain trotting races are very popular in a wide range of countries and more important than thoroughbred races in a number of them. It is important to note that the trotting races do not involve jockeys on the horse's back and instead the driver is sat on a 'cart' pulled by the horse. This important difference is considered further in the 'Changing Gaits' section below.
In Britain trotting is normally used in only relatively limited ways in racehorse training, for example :-
The gaits described so far have all been balanced in that the legs perform the same motion and evenly spaced in time. This leads to the walk, pace and trot being called symmetrical gaits. If we remove the restrictions placed by balancing the movement of the four legs then a large range of combinations are possible, theoretically more than 20 could be used. However, the horse along with most quadrupeds only use two of the variations - the canter and the gallop.
The canter is a three-beat gait in that one diagonal pair of legs hit the ground together and the other two legs are spaced around this double hoof-fall. Figure 5 shows the hoof-fall order when the horse is on the left lead which means that the left front foot reaches further forward than the right front (which is paired with the left rear).
The order shown is the left front landing while the
diagonal pair are still on the ground, the pair lift-off and are started
swinging forward. At this point the horse's weight is moving forward over
the lead front leg only and the push-off of the lead leg propels the horse
into the single airbone phase. The right rear leg has recovered under the
body and lands first followed by the diagonal pair and then the lead front
leg lands later and further forward to start the stride cycle again. If
the horse were on the right lead then the front right leg would reach furthest
forward in each stride and the left front leg would be paired with the
right rear.
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The canter gait will be the one most commonly used during racehorse training. However, it is worth noting that in British training circles the terms 'Canter' and 'Gallop' are not strictly applied to the gaits used in a particular exercise workout. 'Canter' is used for workouts at a range of speeds and also for the strip of ground that the workout is over. 'Gallop' is used for 'fast work' and also for the strip of ground the workout covers.
If we consider a 2yo in January that has been broken, done the basic walking and trotting groundwork and understands the movement commands and control then it will be ready to start the training programme. This will involve a progressive regime of cantering that gradually increases the amount of work and the speed of it. Little training will be done in full gallop by most trainers other than late on in the programme as part of final race readiness preparation.
Initial training may be quite slow canters at a rate of more than 20secs for a furlong, either singly, pairs or in a group depending upon the trainer but normally lead by a compliant older horse. 20sec furlongs equates to just over 22mph. The next stage would be to move on to the 'Normal Canter' rate of 17-18secs per furlong (25mph at 18secs/f). This is called 'Normal because it would be a typical speed for a first workout of the day for an older horse in their normal training pattern.
The programme would later include 'Swinging Canters' at around 15secs/f (30mph), 'Half Speed' at around 14sec/f (over 32mph) and 'Three-quarter speed' at 12.5 to 13secs/f (36mph at 12.5secs/f). The final step up to 12secs/f training would be relatively limited (perhaps 4-6 sets over 2-5 furlongs). It is at this stage that the gait will change to gallop depending upon the ability of the horse.
Two particular points to note are that the top speed for canter and gallop (around 41 mph) are not too different. In wider terms it is also interesting to consider the type and amount of workouts that a trainer will have done with his 2yos before they run. The variation in trainer methods has a direct bearing on their competitiveness on debut and how much room they have to improve in later runs.
Unlike the canter the gallop is a 'four beat' in that each hoof-fall is independent and there is no pairing of the legs. The sequence of the hoof-fall is given in Figure 6. It may be useful to think back to the 'bound' gait of the rabbit to get a mental picture of what the gallop is like. In the bound movement the front and back legs are paired so that the rabbit pushes off simultaneously with both back legs and reaches forward with both front ones. The front legs hit the ground together and provide the base for the hind legs to be lifted and brought underneath the body to start the cycle again.
The gallop is similar but with the major difference
that there is a slight delay (about a tenth of the overall stride time)
between each leg in a front or rear pair landing. If you think of the historical
paintings of horses stretched out in mid-air like rocking horses then these
would be correct if the horse did 'bound'. The slight delay in the landing
of the legs of the front and rear pairings is why those paintings are incorrect.
They knew at the time the paintings were done that the gallop was a four
beat gait so should have known the 'rocking horse' stretch was wrong even
though it required the development of photography to identify the gallop
precisely.
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Note that the offset, in time, between the front legs landing means that the horse can be leading on either its right or left leg. The lead leg is the one that lands furthest forward and provides a base as the whole body pivots over it with the other three feet off the ground. The horse then drives off into the airborne phase off this leg as the rear pair are already being swung forward under the body to land next.
There is one other subtlety that needs mentioning caused by the fact that there is a small offset between the rear legs landing. This offset means that there an an equivalent to a 'lead', and trailing, leg in the rear pair. If a horse is leading with the left leg in front which rear leg will land first? Does the horse have a choice?
The short answer is that the horse only uses one method which is that they 'lead' with the opposite leg behind to the one in front. This is more stable and efficient and is called the 'Transverse Gallop'. The long answer would require going too far off the path to consider the 'Rotary Gallop' where the lead legs are on the same side. This is almost never used by the horse other than perhaps while it is accelerating from a standing start and is still 'sorting its feet out'. It tends to be used by hunting quadrupeds with more flexible spines like the cheetah.
As noted in the section on cantering the bulk of training work will not be done in the gallop gait. A 2yo may have 4-6 sessions of 'fast work' at around 12 seconds per furlong before it races and be the sum total of it's experience in the gait before it runs at the racecourse. Some trainers may put a sprint 2yo through a sharp workout of 2-3 furlongs at sub 12sec/f pace before its debut. This would not be to assist fitness but to ensure it was mentally ready to go the pace it may need to so that it is not outpaced in the early stages of a race.
For the canter and gallop we have seen that the pairs of front and rear legs complete a different overall motion in a stride with different hoof-fall timings. To identify the differences one of the pair of each leg is identified as leading and the other as the trailing leg. By definition the leading leg is the one of the pair that lands furthest forward in a stride. The lead front leg in both the canter and gallop will be the only leg in contact with the ground for a period before the push-off to the airborne phase of the stride. This motion is relatively stressful and tiring to the muscles for that particular leg.
On a straight course there is no reason for the horse to change lead legs other then through fatigue, or possibly though an injury causing it to be uncomfortable to lead on one side. On changing the lead late in a race it is common to see a horse able to find a forward effort relative to another horse. If you watch a race and see a horse appear to slightly hesitate and then perhaps stretch out a little more it has almost certainly changed leads.
When a horse is going around a bend it is most stable turning (leaning towards) the side of its leading leg. Therefore, a horse going around a left hand bend should be on the left lead and the jockey needs to correct it if it is not. If you think of any movement it consists of unbalancing yourself by moving your weight so that you start to fall in one direction. This becomes 'movement' rather than 'falling' because you, or a horse, keeps moving a leg to the correct place to 'catch the fall'. Think about what would happen if you pushed forward off one leg and didn't bother putting the next leg out in front of you. The technical term for this process of unbalancing and catching is Dynamic Equilibrium.
Returning to the horse on the left hand bend it will be leaning slightly towards the left and the jockey should be assisting this lean. The lead leg is the one that lands last and is required to catch that lean towards the left and drive it forward when it becomes the only leg in ground contact. A horse on the wrong lead will tend to hang outwards away from the inside rail.
The final point to be keep in mind is that changing leads does not just refer to the front pair of legs. It will also mean that both of the rear legs change their motion as well. In the canter this is relatively easy to see because the paired diagonal of front and rear legs will switch over. In gallop the horse will normally swap the lead and trailing legs of the rear pair over during the same stride as the front pair. [You may care to work out why the horse would be changing from a transverse gallop to a rotary one if it only changed the lead in the front leg pair.]
This section addresses the question of why the horse changes between the different gaits. For example, if the horse can trot at more than 30mph surely this would be sufficient for most circumstances so why change to canter at speeds well below 30mph? The discussion below looks at the factors from within the horse that make them change gaits. It should be taken as read that the horse will be 'asked' to change gaits by the rider in many circumstances and the overlap in speeds achievable allows this.
The easiest change to deal with is from the walk to the trot or canter. The speed that the horse, or any animal, can walk at has a natural upper limit set because two (or one with humans) of the feet are always on the ground. As with a human, once they are swinging the legs back and forth as fast as they can and using the full stride length, that's it and they cannot go any faster. To move faster you need to add a jump (an airborne section) to the movement to go faster. The main effect is to increase the usable stride length and therefore go above the walk's upper limit.
The change from trot to canter is less easy to explain because the top speed of the canter is only slightly higher. Remember that the trot has two airborne sections in a stride so increasing the effective stride length while the canter only has one. The higher speed in canter is produced because the horse can swing the legs more quickly in canter.
There are two proposed reasons and the first is energy efficiency. Each of the gaits can be used across a wide range of speeds but each has a range of speeds at which they are most energy efficient. Tests have shown that if a horse uses the most efficient gait speed then they use roughly the same amount of energy to move a set distance (a mile for instance). So, part of the reason for moving to a different gait at higher speeds is to do with energy usage.
The second proposed factor is that of impact force on the horse's lower legs and the canon bone in particular (which is between the knee and the joint above the hoof). At higher speeds the gallop produces less loading on the lower legs than the trot or canter would and this contributes to the horse 'knowing' when the change gaits. Tests done with horses weighed down with saddlebags have shown that they will change gaits earlier than they would if unladen but still at roughly the same impact force on the lower leg.
To end this section it is worth mentioning that the horse can change down through the gaits in most combinations as well. As many riders will know to their cost they can go from cantering or trotting to full stop in a stride if they want to. During their normal work canters trainers will usually insist that the riders get them to move down from canter to trot and then to walk rather than the direct canter to walk transition. This is seen as a way to minimise the forces on the legs and to help to avoid injuries.
When writing about judging yearlings at the sales former top 2yo trainer Bill O'Gorman says :-
"The single most important asset in the racehorse is athleticism. .....[in] a choice between an athletic and precocious, but slightly incorrect, individual and an absolutely correct, but inactive and stolid looking one, the athlete should be selected."
However, although it is easy to accept that athleticism is important in the racehorse it is difficult to describe. Mr O'Gorman covered it in two short paragraphs and the 'Paddock Review' section of this site deals with the subject in slightly more length. In general, athleticism is a quality that we feel we understand but when asked to explain it a haziness on what it is and what factors affect it undermine the explanation. In this context this section describes a two-step definition of 'Athleticism' which can then to used as a check against which factors involved can be checked.
Looking at a dictionary definition of 'Athlete' the following are typical :
When preparing the article one person I asked did not try to directly define athleticism but answered - "Colin Jackson setting the 110m high hurdles World Record". This is a useful thought in a number of ways. Firstly it gives a good example of the actual expression of athletic ability that we can agree on as real 'Athleticism' - the quality we are looking to define in the racehorse. Secondly, Colin Jackson was opposed by a range of 'physically fit', 'strong' (many stronger than him), 'muscular' and 'active' individuals who could not match his performance. Assessing the expressed athletic performance is clearly more complex than totalling up the 'parts'.
As the first step in creating a usable measure of Athleticism let us start with two basic definitions :-
With this background we can move on to the second step of producing a usable definition of athleticism. The simplest way is to consider the factors which fundamentally make up, and limit, the cruising and maximum speed of the horse and for how long they can produce them. They are :
STRIDE LENGTH and STRIDE FREQUENCY and EFFICIENCY
This is an important point to grasp. Practically all of the items which go up to make 'Athleticism' and are part of its expression relate to these three factors. Taking this a step further all of the qualities which you have some chance of measuring by visual assessment relate to these areas. When considering any of the large range of proposed items which affect athleticism a good starting point is to ask what they will have on any of the above three factors. If this identifies a concrete, visible effect then you have a chance to devise a method to assess it.
The majority of horse races when run at a solid pace boil down to who can go fastest for longest and this amounts to the one with the best cruising speed. This is a balance between all three of the factors above. Some races are won by horses which can produce an 'effort' later in the race (often at the 2f from home point in British turf racing). This is a relatively short period of increased, maximum, speed. The top speed is directly controlled by the combination of stride length and frequency so can be measured. As an aside the general view is that at the top end of the speed range stride length is the major differentiating factor.
Now that we have the basic definitions and a set of three factors to compare proposed indicators of athleticism against let us try applying them. A common belief in racing is that you can judge athleticism to some extent by how the horse walks and specifically by how much the hoof-fall of the hind legs overlaps with the hoofprint made by the forelegs. This is described in more detail in the 'Paddock Review' part of this website. What link is there to any of the three factors we have identified?
The answer is that it is hoped that this will be a good indicator of stride length that the horse can produce in gallop. The further under the body that the rear legs reach in gallop the longer stride they can produce (up to a point) as they pivot the horse's body over them. How good is the link between overlapping of front and rear hoof-falls in walk and the length of stride they will produce in gallop? I'm not aware of any scientific studies but common-sense suggests there ought to be some correlation. In the absence of 'proof' it is clearly a link that should be used with some caution.
If we consider the same point further what can we expect to see as the horse canters to post or during the race? If we could assess the amount of overlap in faster gaits then the correlation with performance could be better? Trying thinking about this example. Two nearly identical horses are approaching the last furlong of a race absolutely neck-and-neck. They are 'nearly' the same only because one of them is capable of flexing their hips slightly more to enable them to get their hind legs 3 inches further under them in the gallop than the other.
The jockeys ask their mounts for maximum effort and the horse starts flexing his hips fully at exactly the furlong from home point. This horse takes 30 strides to reach the finish so each stride is 22 feet in length. The other horse is taking strides 3 inches shorter and in 30 strides has covered 7 feet and six inches less which amounts to around 1 length and the margin he is beaten by. Hmm, are you really going to be able to spot 3 inches of difference in a horse travelling at 40mph? Or even cantering to the start.
In general the point also needs to be made that the stride length produced by the rear legs has to interact correctly with the timing of the front leg movement. This means that there is not a simple relationship between getting the hind legs under the body and expressed athleticism although it will be a positive factor in many circumstances. What we are more likely to be able to spot are the obviously poor athletes who are not getting their hind legs properly under them.
Having covered hoof overlap in walk we can think about other words that tend to be used to describe what we are looking for in a more athletic horse. The words that tend to come up are 'active', 'fluent', balanced', 'purposeful' and so forth. While they purvey a flavour of the quality they are looking for, other than possibly 'balanced', they are not defining easily visible and measurable characters like hoof overlap.
Applying the rule of asking what affect each one has one one of the three key factors they affect the links are not obviously strong. We can assume that to some level that an 'active' horse (i.e. one that uses its legs and body fully in the walk) has a better chance of showing more athleticism in the race than an 'inactive' one that trudges around. But these descriptions will tend to have an "I'll know it when I see it" feel rather than a measurable association to the key factors.
We can take this approach further into the realms of 'good conformation' advice. If the phrase 'good hip to hock length' is blithely used then what athleticism point is being inferred? Applying the 3 factors approach identifies that what the person is trying to express is that the length and proportions of the hind leg should help in allowing an average, or better, stride length for the horse. In general the use of such a phrase in isolation from a whole range of other factors is of limited use.
With a less technical phrase such as "I like a big, powerful back-end on 'em" the same approach still works. The muscles in the 'buttocks' and loins affect both stride length and frequency. If you look back at the offset timings for trot, canter and gallop you will see that in each gait the hind legs work progressively closer together. The maximum propulsion comes if they both work simultaneously but other considerations such as stability means there will also be some offset. Part of the reason for the higher top speeds in canter and gallop is that the increased propulsion from the buttocks acting together increases stride length by increasing the distance covered in the airborne phase (in effect jumping further). Also, the bigger muscle bulk of sprinters tends to be made up of a greater proportion of fast twitch muscle fibre. As the name implies these can contract more quickly and powerfully so increase the drive (stride length) and take less time to act (increasing stride frequency by being ready earlier to start the next contraction).
The approach can be extended to any other conformation points - back length, shoulder angle, pastern angle, etc. - as well as to the factors in general Paddock Review like size, build and geometry. A major item to remember is that the expressed athleticism is a product of all of the different interactions of all of the different areas which can impact on stride length and frequency along with energy efficiency. The complexities of the interactions mean that attempts to describe and encapsulate athleticism can tend to be woolly.
In a follow-up article athleticism, and how to approach assessing it, will be considered at more length. This will also cover how the horse has developed to be an exceptional athlete even compared to most other animals and the wide range of areas and systems which affect athleticism.
