An Overview of the Biomechanics of the Walk in Horses
Introduction
The walk is the only gait in which there is no suspension; at every phase of the gait there are alternately two or three hooves on the ground (a triple/dual stance or bipedal/tripedal support). This, in addition to its slow speed, makes the walk the easiest gait to ride for beginner riders. The walk has eight distinct movements which are performed in a four-beat rhythm with the hind hooves landing directly in the prints of the front hooves (referred to as “tracking up”). The support sequence of footfalls in the walk beginning with a triple stance that initiates with the left front leg (LF): RH/RF/LH-RF/LH-RF/LH/LF-LH/LF-LH/LF/RH-LF/RH-LF/RH/RF-RH/RF. (Clayton, 2004, p. 171) A bipedal stance always requires one front limb and one hind limb, while tripedal support is either two hind limbs and one front or two front limbs and one hind.
The ideal walk for a horse, especially a dressage horse, should have all the supple synchronicity of the jungle cat. As there is no suspension in the walk, the biomechanical action in the gait is simply the action of advancing and retracting the limbs to move the horse across the ground. (Clayton, 2004, p. 172) While the walk may seem “boring” and simple due to its lack of speed, the biomechanical coordination for a healthy, athletically useful walk is just as complex as the more visually impressive gaits.
Initiation of the Walk
To move from a halt into walk, the horse must do more than simply move its feet. The horse must first shift its weight forward until it becomes unbalanced enough to necessitate the movement of its feet. Walking is therefore the process of many small falls forwards over the horse’s center of gravity. This movement is organically initiated by the movement of the head and neck. (Blignault, 2009, p. 166)
The well-trained riding horse will be able to begin the walk by moving its hindquarters forwards and stepping under its center of gravity and then pushing forward, rather than falling forwards and catching the movement with a front limb. This is the “on the bit” halt-walk transition, in which the horses head and neck will have a distinct arched look and the horse will move its body as a coordinated unit. The on the bit walk requires an enormous amount of biomechanical coordination, as the horse must not only navigate the complexity of the gait itself but must do so without relying on its natural use of the head and neck to advance it’s body. (Blignault, 2009, pg. 167)
As the speed of the walk increases, the periods of bipedal and tripedal support alter from equal time to the horse spending more time in the bipedal support phases and less in the tripedal stances. This is a result of the overall shortening of stance durations of the limbs individually, which results in less overlap between limbs (and when done without proper physical coordination can ruin the “tracking up” of a horses walk). (Clayton, 2004, p. 172)
Biomechanics of the walk (See Fig 1 and 2)
To advance a front leg the elbow must flex, the scapula retracts, the forelimb lifts and advances, the foot lifts and the knee bends. The elbow is flexed by the biceps, which connect from the scapula to the radius, and the brachialis, which connects the humerus to the radius. The foreleg is raised by the large brachiocephalus muscle which runs from the atlas to the humerus and levers the foreleg up. Retracting the scapula involves moving it both down and back, and is mainly accomplished by the serratus ventralis (thoracic), which attaches the scapula to the ribcage. Flexors at the back of the knee lift the foot and bend the knee. When the foot is lifted off the ground, it is suspended by dorsal scapular ligaments and the trapezius. (Pilliner et. al., 2002, p. 92)
After a front leg is lifted, it is straightened by the shoulder supraspinatus attached to the scapula and humerus, while the elbow is managed by the triceps. The lower leg (knee, fetlock, pastern, coffin joints) are straightened by carpal and digital extensors. The straight limb then is places back on the ground when rigid. The body is then moved over the rigid limb until body weight and the advance of the stride causes the leg to be lifted again. (Pilliner et. al., 2002, p. 93)
The hind legs are influenced by the connection from the pelvis to the vertebral column, and the integrity of the walk depends heavily on the biomechanical soundness of this connection.
The initial flexion of the hip joint carries the femur and stifle forwards. The stifle flexes first, leading to flexion of the hock. The gluteal muscles and the biceps femoris extend the hip, while the semitendinosus flexes the stifle. Peroneus tertius flexes the hock. A contraction of the tibialis anterior contributes to hock and stifle flexion. (Pilliner et. al., 2002, p. 93)
One the limb has moved up and forwards underneath the horse towards it’s center of gravity, the stifle is extended by the quadriceps femoris muscle group. The hock simultaneously extends via the tendinous superficial flexorand tendinous cord in the gastrocnemius.
As with the front legs, the hind leg is rigid when it enters the stance phase. The limb locks, with rigid muscles stabilizing the stifle and hip joints. As the limb approaches vertical in the stance phase, the stifle and hock flex and the fetlock joint sinks to facilitate shock absorption. This becomes more visually apparent as the limb passes vertical. When the limb has passed vertical, the “haunch” and hamstrings extend the hip, stifle, and hock. When the body has moved forward in the next stride, the hoof leaves the ground the ground, and the peroneus tertius and tibialis anterior semiflexes the hock through elastic recoil to prepare the limb for the next stride. (Pilliner et. al., 2002, p. 93)
Lameness
This complex interplay of muscles, tendons, and ligaments all levering the extending the skeleton to produce forward movement is very interdependent. Any problem with any of the muscles involved creates a fault in the gait, which can simply make is less desirable for competition (such as dressage) or lead to lameness. (Pilliner et. al., 2002, p. 96)
For example, a weakness in the trapezius would cause the front legs to not be held off the ground for as long, which could lead to prolonged stance phase ad interference of the front and hind limbs (forging or overreaching). An overreaching horse can injure themselves severely by knocking a hind hoof into sensitive soft tissue of the forelegs, or any other configuration of interference.
In this way the walk is a good gait to assess the overall fitness and soundness of the horse, as many problems can be identified without the potential to aggravate injuries that can happen with the faster gaits of trot and canter. However, it is important to remember that some lameness can only be identified in faster gaits for the exact same reason.
Because the horse uses a vast number of muscles while walking, and the lack of suspension results in low concussion, walking is the gait of choice for rehabbing injuries. An active, free moving forward walk is ideal for warming up the horse and relieving tension, as the back “swings” freely. It is an excellent way to rest muscles between bouts of strenuous work. (Blignault, 2009, p. 170)
Quality of the walk within disciplines
Dressage is the only discipline (aside from obscure breed-specific showing) which directly gauges the quality of the walk as criteria for the quality of the horse during competition. Walk, trot and canter are of equal importance in the dressage arena.
A good walk for a dressage horse is quantified by a consistence four-beat rhythm and overtracking steps (not to be confused with overreaching and interference). Each foot should be placed on the ground without hesitation. The four-beat rhythm means that the intervals between each footfall should be identical in timing. The length of strides should also be similar. The hooves should not be dragged along the ground. Overall, there should be a picture of “thoroughness” to suggest athletic capability.
The walk in competitive dressage has four distinct variations: free, extended, medium, and collected. The free walk is designed to show the horses walk as its loosest and most unrestrained, and is the only time in competition when the horse is given freedom of the head and neck at the walk. The extended walk should show an obedient lengthening of the stride. Medium and collected walks called for a shortened stride while maintaining the integrity of the gait such as suppleness, overtrack, and rhythm. Medium and extended walks are often faster in tempo that collected walks because the increased stride length often leads to a quicker stride rate. The difference in stride rate and tempo between medium extended walks is often small. The free walk is often faster because of the freedom of the head and neck allows the horse to initiate forward movement more easily. Lengthening of the stride in the walk involves the horse moving it’s body farther over the grounded hoof in the stance phase because there is no suspension in the gait. (Clayton, 2004, pg. 172)
Faults at the walk
The competence of the rider and the fit of the saddle are huge factors in the quality of a dressage horse’s walk. If the saddle interferes with a muscle group or prevents movement of the scapula, it can ruin the integrity of the walk. However, it is the rider who is most often to blame for a sub-par walk. Young, unbroken horses almost never have a “bad” walk. (Blignault, 2009, p. 172) The four-beat walk is often diluted or destroyed completely in the process of training a dressage horse to perform high-level movement; sacrificed for a more expressive trot and canter. A well-trained horse will not try to use its head and neck to walk forwards, while a young horse will. A rider who does not understand this may try to treat the young horse the same way they would an older horse who tried to use its head and neck improperly and hold the head down in an attempt at correction. To the young horse who has not learned the coordination to walk on the bit, this gives two conflicting messages: walk forwards and stop. This can lead to tension and problems with the gait. (Blignault, 2009, p. 173)
Common problems with the walk are overly hurried strides, the shuffle, and pacing (also known as a lateral walk). When a rider asks a horse to move more quickly in the walk without ensuring that the hindquarters are moving up to the front end, the horse ends up rushing along the ground and becoming “strung out.” This is the result of tension in the topline (back) muscles. This can be corrected by slowing the walk, then gently asking for forward movement into a very soft hand. (Blignault, 2009, p. 173)
The shuffle is the result of anticipation. When the horse receives (or expects to receive) the aid for a faster gait, it will take several uncoordinated, fast steps to organize it’s body for the transition. This is usually the seen in lower level horses who are still building the muscles they need for smooth, balanced transitions. It is very common when the horse first starts to be school in a walk to canter transition. If the rider attempts to correct this with a firmer rein contact, the result may be that the problem worsens. Relaxation and conditioning are the most effective ways to correct this error. (Blignault, 2009, p. 172)
The pace or lateral walk is the most unfortunate fault in the walk and potentially the most difficult to correct. While some specialized breeds of horses are bred to pace naturally, it is almost always highly undesirable. Some dressage horses show incorrect lateral couplets when walking. (Clayton, 2004, p. 172) When a horse walks laterally, it moves lateral pairs of legs simultaneously. Pacing happens when either the front limbs move too quickly or the hind limbs move too slowly. Often it occurs because a rider has taken a firm hold on the reins to correct some other problem, neglected to half-halt often enough (not allowing energy out or rebalancing the horse) and inadvertently caused a pace. The rider must determine whether to slow the front legs or speed up the hindquarters to correct the pace. (Blignault, 2009, p. 173)
Conformation
Conformation plays a large role in how a horse moves (although it is not always the defining factor). Horses with short backs and long legs, for example, will usually have a much easier time achieving the ideal function at the walk. This is because a short back makes it much easier for a horse to track up. Horses with long backs and short legs will likely not be able to walk in a way to earn them high scores in dressage, although they may be just as functional from a purely biomechanical point of view. Since tracking up is very dependent on conformation, it is not a good sole indicator of the biomechanical correctness of the walk. (Pilliner et. al., 2002, p. 97)
Another competitive discipline which values the walk is endurance. Endurance horses must cover a huge amount of ground in a specified window of time, and walking is a good way to progress without undue wear and tear on the horse. This means that a large stride is valuable, as it allows the horse to cover ground quickly. A very good endurance horse can walk at the speed some other horses trot.
Conclusion
In conclusion, the walk is a very complex gait with myriad factors that contribute to its quality and functionality. Almost all horses are born with a naturally “clear” four-beat walk. Care must be taken on the part of the rider not to disrupt the function of the walk in the process of training.
Sources:
1. Back, Willem, and Hilary M. Clayton. Equine Locomotion. 2nd ed. Saunders Ltd, 2013. Print.
2. Blignault, Karin. Equine Biomechanics For Riders: The Key to Balanced Riding. J. A. Allen, 2009. Print.
3. Clayton, H.M. The Dynamic Horse: A Biomechanical Guide to Equine Movement and Performance. Sport Horse Publications, 2004. Web.
4. Pilliner, Sarah, Samantha Elmhurst, and Zoe Davies. The Horse in Motion: The Anatomy and Physiology of Equine Locomotion. 1st ed. Wiley-Blackwell, 2002. Print.