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• GAIT = the coordination pattern of a horse’s movement
• STRIDE = basic unit of movement
  • STANCE phase = period during which the hoof is on the ground
  • SWING phase = period during which the hoof is going forward above the ground towards the next stance phase (and the beginning of the next stride)

During the stance phase, there is NO velocity to the hoof. During the swing phase, the hoof is moving MUCH faster than the horse’s body—approximately twice the velocity of the horse’s body. The acceleration/deceleration forces are MASSIVE. A racehorse does the accelerations/decelerations 12x/second. The pulling forward of the leg to the maximum point is called PROTRACTION, and the maximum forward velocity of the hoof is equal to the forward velocity of the horse. The horse will pull the hoof back slightly prior to hoof strike to reduce hoof velocity prior to hoof contact, in what is called RETRACTION.

In DRESSAGE, the swing phase in important to the aesthetics of our sport, but as with the racehorse, the leg will be retracted before it reaches the ground. The ELBOW is the important joint for expression for both protraction and retraction, coming from the TRICEPS muscle.

Videos were shown of Bonfire and Evento. Bonfire demonstrated that although we typically think of the shoulder, if we look in slow motion, the elbow is moving a lot more than the shoulder in an expressive trot gait. Evento demonstrated that a “toe flick” is a whiplash effect, because the elbow has reached its maximum protraction and retraction begins but the lower leg is relaxed and is still moving forward. The “whiplash” results in the effect we call a “flicking” of the toe.

At the end of the swing, contact occurs. The optimal contact is slightly heel first, but there are exceptions. Toe first carries the risk of tripping except in piaffe and for the new trailing leg in lead changes. Changing the trim of the hoof can change the hoof strike pattern. Horses try to place the horizontal surface of their coffin bones flat on the ground. If the heel is too LONG, they will land flat-footed. If the heel is too SHORT, or the toe is too LONG, they will land toe first. Foot pain will also alter how a horse lands.
The hoof is moving forward and downward at contact and must immediately decelerate at contact. The energy enters the locomotor system and travels up the limb in the form of a shockwave, potentially damaging bones and joints. It is attenuated by body tissues, first the laminae of the hoof, then blood flow through the hoof, then joint cartilage and finally subchondral bone.

Adaptation vs. Injury: we use shock to strengthen our horses during our conditioning programs, and when used properly, we can build a stronger athlete. However, if we do not allow adequate time for healing, injuries accumulate and we get breakdown instead.

Racehorses are subject to high impact shock that leads to fatigue fractures of long bones and subchondral bone sclerosis in short bones. Both can proceed to complete fractures.

Dressage horses are subject to a diverse loading environment, but still suffer from impact shock and repeated trauma to cartilage and bone, which ultimately leads to DJD (osteoarthritis). This is the most common cause of premature retirement. Impact shock depends of speed, shoes (steel is worse; some pads decrease shock), and the surface worked on. When the horse contacts the surface, the hoof decelerates. It is preferable to decelerate more slowly. Sand allows the hoof to slide in a little bit (vs. concrete, asphalt or other less forgiving surfaces). Good turf is also forgiving, but if too dry, it can be as bad a concrete, and if too wet, it is too slippery. Additives can be added to sand that can make it even better.

Ground Reaction Forces (GRF) components:

• Vertical: this is the part that overcomes gravity, i.e., the projects the horse in the airborne phase
• Longitudinal: slowing down/speeding up
• Transverse: side to side: comes into play for lateral work/circle work. Not discussed today.

Vertical: maximal as the horse’s weight accepted onto the grounded hoof and the fetlock lowers and the horse’s body lowers over the hoof. It then subsequently decreases again. It occurs during the stance phase, as the horse’s weight is loaded onto the hoof, then rolls forward as the fetlock sinks and the shoulders are lowered. The sinking of the fetlock is proportional to the vertical force, and may even TOUCH THE GROUND!

Longitudinal: Initially, this is a braking force (the cannon bone is angled backwards) then as the angle of the cannon bone changes, it becomes a propulsive force. Braking: think refusals, propping for bucks. Propulsive: think draft horses leaning into the traces. Horses can choose to minimize either braking or the propulsive phase depending on what they’re about. In dressage horses: the hind legs are predominantly used for propulsion, while the forelegs are used predominantly for braking, which gives us our collection and the ability to raise the forehand. As the horse increases in collection, the forelimbs provide more and more braking forces, raising the horse through the withers, while the hindlimbs provide forward propulsion. Without the forelegs working hard to maintain the elevation, the horse would fall on the forehand—collection does not come solely from the hindquarters.

Tempo and Rhythm

Tempo is the stride rate in strides per minute.
Rhythm is the timing of the footfalls, consisting of the number of footfalls per stride, and the elapsed time between footfalls.

The walk is a 4 beat rhythm, the canter is a 3 beat rhythm, and the trot is a 2 beat rhythm. Passage, piaffe and reinback are also 2 beat rhythms.

Rhythms can be either regular or irregular. Canter is irregular. Walk should be regular, but not all horses perform it as such. Trot, piaffe and passage are all regular.

WALK:
The normal walk is a 4 beat regular rhythm WITHOUT an aerial phase (Dr. Clayton no longer talks about suspension). There are always 2 or 3 legs on the ground. The faster the walk, the greater amount of time there are only 2 legs on the ground. The normal pattern is Hind, front on same side, then opposite hind, then front on that side. Two different types of aberrant walks occur:

• Lateral couplets, in which the front leg leaves the ground too quickly.
• Diagonal couplets, which occurs in short-strided walks, because the front leg is too SLOW to leave the ground.

In studies that Dr. Clayton has done on videos of Olympic Horses from the Barcelona and Atlanta Olympic games, Dr. Clayton found that most horses walk faster at extended walk but usually not enough to be visibly noticeable. Average speeds were 52 at collection, and 57 for extension. She also found that in the walk pirouette, the initial steps were fine, but that the rhythm became irregular, the inside hind placement tended to be early, and that the exit step tended to slow to 48. There were also longer stance durations to maintain balance, and more periods of 3 legs support with some periods of 4 leg support.

TROT:
The trot is a 2 beat diagonal gait with a regular rhythm, and 2 aerial phases per stride. In Olympic horses, the speed of the collected trot was 77, while the extended trot was 83. Nearly all of the Olympic horses showed “diagonal dissociation” meaning that on careful video analysis, the front and hind legs did not land at exactly the same moment, but rather the the hind hoof landed slightly sooner—this was indicative of uphill balance. Of all the horses analyzed, Rembrandt had the largest degree of positive diagonal dissociation.

REINBACK:
This is a retrograde diagonal movements, with the footfalls often slightly dissociated. There is no aerial phase. In the Grand Prix, the pattern of the movements requires a good bit of coordination:

Diagonal back, then
4 beat walk forward, then
Diagonal back, then
Trot forward = diag

The vast majority of the Olympic horses had difficulty in performing this cleanly. If you look at the video in slow motion, you see that in the first step backward, the hind is often early, and the transitions between the movements are not clean—attesting to the coordination required.

CANTER:
The canter is a 3 beat irregular movement, with a prolonged aerial phase. The first beat is the outside hind, followed by the inside hind/outside front, and then the inside front. The pause (and source of the irregularity) is due to the aerial phase. The increase in stride length comes from increasing the length of the airborne phase, so that the footfalls must occur more rapidly in order for the tempo to remain the same. In the canter, the body must roll forward over the forehand while the horse is on the ground. In dressage, however, we are teaching our horses not to do that. How do they manage it?

Dr. Clayton showed a video of Rembrandt. In it, we could see that his whole body sinks up until the leading foreleg hits the ground. At that point, he uses his shoulder girdle muscles to lift his entire body (much as a jumping horse does when he reaches a fence), maintaining the uphill nature of the canter. The trailing foreleg initiates this. In the collected canter, the foreleg barely comes back beyond the vertical before it has pushed off and is coming off the ground.

In the canter pirouette, the tempo is usually much slower than the collected canter. At the Olympics, the speed was 66 vs. 96 for collected canter. Canter pirouettes are a 4 beat rhythm, and have no aerial phase.

Piaffe and Passage were 55 strides per minute for Olympians. Passage is a 2 beat diagonal rhythm, with 2 aerial phases per stride. There is well-marked diagonal dissociation, with the front leg coming off the ground early. Piaffe is a 2 beat diagonal rhythm, but there is NO aerial phase.

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