Handedness - can we train a completely symmetrical horse?

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The dominant limb - can we train a completely symmetrical horse?Limb dominance, handedness and laterality are all terms closely associated with the functions of the left and right hemispheres of the brain and how these may influence preferred use of one side of the body; a direct example in humans would be the preferred hand he/she learns to write with or foot to kick a ball with. The racehorse is often commemorated on their speed or ability to clear a fence, but you would be surprised how relevant limb dominance is to the performance and longevity of a racehorse’s career. This preference is often evident in an individual horse’s preferred canter lead, preferred leading limb in gallop, leading and landing limb over a fence. It can be argued that the former activities can be influenced by training, but to what degree and at what point should we utilize this preference? And when should we pay attention to the risk of injury? This article is going to discuss this relevance and explain the potential implications of limb dominance.As with many corners of equine research, the observed phenomenon first began from studying the human and has since been studied extensively in performance and leisure horses, respectively. The goal of many a ridden horse is symmetry of movement, the discipline in which they train will dictate the degree of importance of this; the dressage horse can lose palpable marks when they are not symmetrical in their movement, whilst a racehorse may not be as well versed nor will it be a direct measure of performance quality.Anatomical structure of a horse’s brainThe primary motor cortex is the central hub of dynamic movement, generating nerve impulses that control the execution of all movements and crossing the body’s midline to activate skeletal muscles. Every part of the body is represented and arranged somatotopically, meaning the area controlling the hoof is close to the area controlling the limb. The amount of brain matter or cortical space devoted to a body part represents the degree of control the horse has over that body part. For example, the human will have far greater cortical space devoted to intricate movements of the hands and fingers compared to the horse. In contrast the horse will have far greater cortical space reserved for movement of the ears, lips and nose to represent the vast number of social cues, foraging behaviors and body language exhibited. Although not yet proven in horses, human athletes have been shown to have increased cortical thickness in areas correlating with athletic ability or skill; this is likely to be the case in equines; for example, racehorses would likely see increases in areas devoted to limb control.From a lateralization perspective, the brain is divided into two hemispheres or lobes which are referred to the left and right hemispheres and divided by the corpus callosum. The corpus callosum is an essential structure composed of a thick band of nerve fibers providing communication between the two spheres. Lateralization refers to these hemispheres having distinct functional differences, each offering specialized neural functions or cognitive processes. Lateralization occurs contralaterally, meaning that a horse who is left hemisphere dominant will experience a right-sided motor preference and vice versa.What research is there on limb dominance?In horses, grazing patterns are often studied, specifically noting which limb is placed forward most often; however, research is varied with some conclusions stating that innate skeletal asymmetry is highly prevalent in the foal and can be exacerbated by environmental factors. It is recommended that a farrier and vet work closely to correct visual asymmetry in goals as early as possible. A valuable longitudinal study completed by Van Heel et al., (2010) found a relationship with uneven forefeet in foals and subsequent unevenness as a yearling and then as a three-year-old; this was then found to correlate with sidedness in trot and canter transitions. This study highlights several points of interest, firstly the distinct need to correct limb asymmetries and abnormalities from an early age and secondly the potential future inclusion of quantitative laterality data at the time of studbook admission to assist breeders and owners in selection criteria.Later research by Austin and Rogers (2012) stated there was no significant differences in limb dominance in a group of feral and wild Przewalski’s horses, which suggested that differences can be attributed to domestication at least to some degree. This varying body of evidence opens the discussion on the effect of domestication and relevance of cultural husbandry practices; in the western world it is common practice to complete many routine tasks from the left side of the horse, e.g., leading, tacking up and mounting. Future studies that attempt to measure this cultural influence may choose to select a large group of equines of generally the same breed and discipline to act as a control and prevent skewed results.Many studies have attempted to decipher the causes of variation in motor bias. This is yet to have solid evidence behind it, with several studies showing links in gender and breed initially with training likely to play a part as they embark on their ridden career. As with all equine research, it is important to take note of cause and effect; for example, it may not be the fact that the horse is of Thoroughbred breeding, but the likely type of work or environment that a Thoroughbred is placed in that has supplied the correlation.The gallopAs many a rider and trainer will describe, a horse will naturally have a leading limb preference and over a fence, they are generally left to continue with their preference; on the flat, generally left to the jockey’s discretion but the consensus seems to be less interference the better. Then comes the bends. In the transverse gallop, the horse will have a four-beat gait—a pattern of right hind, left hind, right fore, left fore—with the left fore essentially leading the movement and acting as the leading limb round a left hand bend. In the words of Dr. Ray Baran, the correct lead is “the easiest method to get the shortest distance between two points the quickest way”; as a result the horse is in balance.Clockwise or counterclockwise?Laterality research in the racing Thoroughbred has paid special attention to racetrack direction. This is specifically relevant given that in Europe, racetracks are both clockwise and counterclockwise, some with greater curves and in some cases horses race for one mile in a straight line. Meanwhile, in North America, where all tracks are counterclockwise, largely oval and flat, there is greater potential for laterality and limb dominance to be magnified due to horses racing consistently in the same direction. In addition, from a performance point of view, it is unlikely horses will be trained in the opposite direction to counteract any developmental preferences.Anecdotal evidence suggests there is an emerging understanding of the implications of asymmetry in the horse, with more trainers beginning to pay special attention to ensuring horses are as symmetrical as possible during their training.Simple alterations to training regimes include:Training horses in both clockwise and counterclockwise directionWorking horses centrally rather than allowing them to develop a dependence and “lean” on one rail.Adding variety to fitness routines which may include use of an aqua treadmill, providing cardiovascular training without repetitive or concussive force through limbs.Adding gymnastic jump exercises or gridwork, again providing athletic benefit whilst not repeating the same dynamic patterns of movement.Does a horse’s standing posture correlate with their dynamic performance?Static posture and conformation are not always indicative of how a horse will then move dynamically, and vice versa, some limb deviations will only be present in stance as will deviations in the flight path of a limb only be visible in motion. Further to this, some will only be present in certain gaits.Research released in the last eight months from Holleboom (2020) at Massey University, New Zealand conducted a small study looking at load distribution in the forelimbs of horses either clockwise or counterclockwise. Although no significant differences between left and right limbs were found, this is only indicative of static weight bearing and during dynamic exercise. This may well change when other external variables are also in place such as racing environment, rider aids and other horses present amongst others.Several researchers conducting thesis studies have also looked at facial hair whorl direction as a measure of laterality and found it to be indicative of greater forelimb weight load distribution. Research by White (2018) found that a horse with a clockwise whorl direction preferred to load the right forelimb more; comparatively, the left forelimb was favored in horses with counterclockwise whorls. Interestingly, the study also found links between forelimb loading preference and cannon bone circumferences when measured externally. Gohery (2017) found correlative links between whorl direction and desirable stride characteristics in canter. Horses with clockwise whorls had a longer stride in the left stride pattern, and horses with counterclockwise whorls had a longer stride in the right stride pattern. Initially the two studies appear to contradict themselves, but we must remember the canter is a three-beat asymmetrical gait initiated by the opposite hind leg from the leading forelimb. Therefore, this study corroborated the work of White and other previous researchers.Dynamic exercise is of particular relevance given that the force exerted through the leading forelimb at gallop has been shown to be as much as twice the horse’s body weight; and this may be relevant when considering the potential implications for a horse that is significantly preferred of one limb.So, what does this mean for the horses that I train?The prevalence of repetitive strain injuries and stress fractures in the sports horse, and in particular racehorses, has been widely documented for the last 40 years—occurring most commonly in the third metacarpal, third metatarsal, humerus, tibia, and proximal phalanx. These locations have been proven to be anatomically and biomechanically susceptible to excess wear and tear, rendering them at risk of stress fracture. But what has not been identified is the relationship between these sites of fracture and if the fractured limb were indeed the horse’s dominant or preferred limb. Emergence of this research would better inform us how to improve training practices to prevent such fractures.The use of ground reaction force measurements and force vector diagrams have been shown to identify inter-limb asymmetries in preliminary studies by Hobbs et al., (2018) which shows a reliable method of being able to further conduct these studies in the future. If paired with the work of Holleboom, this may begin to provide the equestrian industry with some answers on this topic and therefore better inform best training practice.And what about rider influence?Of course, we must also consider the influence of the rider who themselves will no doubt have their own dominant limb which may influence the aids given to the horse and which over time may increase the effects of laterality or potentially even it out. Currently scientific evidence would be hard to come by in-field due to the difficulty in separating rider laterality and horse laterality, but it is certainly a topic for development in the future.In summaryHaving discussed the available and emerging research and its potential implications we are left with a causality dilemma or informally known as the “chicken or egg” situation, where we have scientific evidence of the existence of laterality in horses but currently lack data that solidifies cause and the potential implications. Until we have this solid evidence, we can begin to work with existing and anecdotal evidence and current best practice to train our horses to be as symmetrical as possible to minimize risk of the detrimental effects of extreme lateralization. The appreciation and relevance of limb dominance may seem like a small cog in a large wheel of the performing racehorse, but when the aggregation of marginal improvements to performance is at the forefront, can we really afford to ignore its potential significance?

By Georgie White


The dominant limb - can we train a completely symmetrical horse?

Limb dominance, handedness and laterality are all terms closely associated with the functions of the left and right hemispheres of the brain and how these may influence preferred use of one side of the body; a direct example in humans would be the preferred hand he/she learns to write with or foot to kick a ball with. The racehorse is often commemorated on their speed or ability to clear a fence, but you would be surprised how relevant limb dominance is to the performance and longevity of a racehorse’s career. This preference is often evident in an individual horse’s preferred canter lead, preferred leading limb in gallop, leading and landing limb over a fence. It can be argued that the former activities can be influenced by training, but to what degree and at what point should we utilize this preference? And when should we pay attention to the risk of injury? This article is going to discuss this relevance and explain the potential implications of limb dominance.

As with many corners of equine research, the observed phenomenon first began from studying the human and has since been studied extensively in performance and leisure horses, respectively. The goal of many a ridden horse is symmetry of movement, the discipline in which they train will dictate the degree of importance of this; the dressage horse can lose palpable marks when they are not symmetrical in their movement, whilst a racehorse may not be as well versed nor will it be a direct measure of performance quality. 

Anatomical structure of a horse’s brain

shutterstock_1507412945 (2).jpg

The primary motor cortex is the central hub of dynamic movement, generating nerve impulses that control the execution of all movements and crossing the body’s midline to activate skeletal muscles. Every part of the body is represented and arranged somatotopically, meaning the area controlling the hoof is close to the area controlling the limb. The amount of brain matter or cortical space devoted to a body part represents the degree of control the horse has over that body part. For example, the human will have far greater cortical space devoted to intricate movements of the hands and fingers compared to the horse. In contrast the horse will have far greater cortical space reserved for movement of the ears, lips and nose to represent the vast number of social cues, foraging behaviors and body language exhibited. Although not yet proven in horses, human athletes have been shown to have increased cortical thickness in areas correlating with athletic ability or skill; this is likely to be the case in equines; for example, racehorses would likely see increases in areas devoted to limb control. 

From a lateralization perspective, the brain is divided into two hemispheres or lobes which are referred to the left and right hemispheres and divided by the corpus callosum. The corpus callosum is an essential structure composed of a thick band of nerve fibers providing communication between the two spheres. Lateralization refers to these hemispheres having distinct functional differences, each offering specialized neural functions or cognitive processes. Lateralization occurs contralaterally, meaning that a horse who is left hemisphere dominant will experience a right-sided motor preference and vice versa. 

What research is there on limb dominance? 

In horses, grazing patterns are often studied, specifically noting which limb is placed forward most often; however, research is varied with some conclusions stating that innate skeletal asymmetry is highly prevalent in the foal and can be exacerbated by environmental factors. It is recommended that a farrier and vet work closely to correct visual asymmetry in goals as early as possible. A valuable longitudinal study completed by Van Heel et al., (2010) found a relationship with uneven forefeet in foals and subsequent unevenness as a yearling and then as a three-year-old; this was then found to correlate with sidedness in trot and canter transitions. This study highlights several points of interest, firstly the distinct need to correct limb asymmetries and abnormalities from an early age and secondly the potential future inclusion of quantitative laterality data at the time of studbook admission to assist breeders and owners in selection criteria. 

Later research by Austin and Rogers (2012) stated there was no significant differences in limb dominance in a group of feral and wild Przewalski’s horses, which suggested that differences can be attributed to domestication at least to some degree. This varying body of evidence opens the discussion on the effect of domestication and relevance of cultural husbandry practices; in the western world it is common practice to complete many routine tasks from the left side of the horse, e.g., leading, tacking up and mounting. Future studies that attempt to measure this cultural influence may choose to select a large group of equines of generally the same breed and discipline to act as a control and prevent skewed results. 

Many studies have attempted to decipher the causes of variation in motor bias. This is yet to have solid evidence behind it, with several studies showing links in gender and breed initially with training likely to play a part as they embark on their ridden career. As with all equine research, it is important to take note of cause and effect; for example, it may not be the fact that the horse is of Thoroughbred breeding, but the likely type of work or environment that a Thoroughbred is placed in that has supplied the correlation. 

The gallop

_ a 011 Social Paranoia _ Poker Belmont 20200704-.JULY 04, 2020 _ Social Paranoia with Jose Ortiz aboard, wins the Grade 3 Poker Stakes, going 1 mile on the turf, at Belmont Park, Elmont, NY.jpg

As many a rider and trainer will describe, a horse will naturally have a leading limb preference and over a fence, they are generally left to continue with their preference; on the flat, generally left to the jockey’s discretion but the consensus seems to be less interference the better. Then comes the bends. In the transverse gallop, the horse will have a four-beat gait—a pattern of right hind, left hind, right fore, left fore—with the left fore essentially leading the movement and acting as the leading limb round a left hand bend. In the words of Dr. Ray Baran, the correct lead is “the easiest method to get the shortest distance between two points the quickest way”; as a result the horse is in balance. 

Clockwise or counterclockwise? 

Laterality research in the racing Thoroughbred has paid special attention to racetrack direction. …

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