Mechanical stresses (movements) are critical for the control of tissue form and function. Muscles and bones actively remodel in response to changes in exercise and response to mechanical stresses. This is actually a fundamental feature in all living tissue.
Experiments with cultured cells confirm that mechanical stresses can directly alter many cellular processes, including signal transduction, gene expression, growth, differentiation, and survival.
To understand this process of mechanoregulation, we must take into account that living organisms are constructed from tiers of systems within a system within a system. For instance, a limb is composed of bones, muscles, blood vessels, nerves, etc. These in turn, are constructed from muscle fibers, vascular endothelium, and connective tissues, which are composed of groups of living cells and their associated extracellular matrix.
Extracellular matrix are macrocellular complexes composed of different collagens, glycoproteins, and proteoglycans that function as in-vivo scaffolds for cell anchorage. We could scale further with cell components and composition of the cell’s components, but this would be out of the scope of this discussion.
At right is a diagrammatic view at progressively smaller size scales within the tensegrity structural hierarchy of a ligament from an articular joint.
A pre-stressed balance of continuous tension (T) and compression (C) elements stabilize the physical structure at several size scales.
(Tensegrity structures are characterized by use of continuous tension and local compression. Prestress = Internal stress before application of external force.)
Top – Bones and ligaments.
Middle – (Two middle views), Contractile cells and local regions of tensionally-stiffened ligament extracellular matrix.
Bottom – Contractile microfilaments and microtubules act as balanced tension and compression elements, respectively.
Remark: an element placed under tension and at one size scale can act to resist compression on a smaller size scale.
As well, asking for lateral bending of the horse’s vertebral column acting on the neck may achieve some lateral bending at one scale, but induces inverted rotation on another scale.
“In the cervical and thoracic vertebral column, rotation is always coupled with lateroflexion and vice versa.” (Jean Marie Denoix, DVM. PhD, Spinal Biomechanics and Functional Anatomy, 1999)
Injecting the horse’s hocks or stifles with hyaluronic acid or other drugs might provide transient relief at one scale but the root cause of the problem resides at another scale.
“The long-standing inability to effectively alter the structural damages in knee osteoarthritis with the current therapeutic paradigm is the result of a persistent overemphasis on articular cartilage as the primary outcome of joint failure. This myopia has been misdirected and fails to address the root cause of the disease. Although its etiology is likely multifactorial, it is now generally accepted that osteoarthritis onset and propagation are mediated largely through biomechanical forces acting across the joint and the failed repair of damage caused by excessive mechanical stresses and loading on joint tissues.” (Craig Waller, David Hayes, Jon E. Block, Nicholas J. London. Unload it: the key to the treatment of knee osteoarthritis. 2011)
In 1986, Jean Marie Denoix correlated the torque induced on the third metatarsal bone with the development of osteoarthritis in the hock joint.
“Preferential support of the hoof on the inside wall during ground contact and push-off concentrates compressive forces on the internal face of the hock joint, where the articulation is particularly prone to degenerative phenomena (arthritis) leading to spavin.” (Jean Marie Denoix, Biomechanique et travail physique du cheval de sport. 1986)
In the same line of thought, releasing a muscular pain might help the horse at one size scale but might create instability at another. The main function of the back muscles during locomotion is to preserve the integrity of the vertebral column’s structure. Some equestrian theories emphasize the relaxation of the horse’s back muscles. If such relaxation were achieved, the theories would compromise the integrity of the horse’s thoracolumbar spine.
“A major cause of lameness is lameness.” (James R. Rooney)
Beside the very well know fact that the benefits of static therapies are altered by trainers and riders submitting their horse’s back to the training misconception that created the injury in the first place, the dimensions offered by modern research studies underline the need for acting at all the different levels of the horse’s biological structure, include mechanical stresses (exercise).
As a wild animal, the horse owed his survival to his capacity of outrunning all his predators. A cheetah may be able to sprint faster, but for a short distance. Given enough warning and in spite of his large size and weight, the horse is capable of running faster and further away. This survival peculiarity demands extreme anatomical adaptations, down to the chemical components fueling or cleaning the muscles. The benefits of mechanical stresses (exercise) are involved at all levels of the horse’s structural hierarchy. For instance, skeletal muscles possess two main types of monocarboxylate transporters, MCT 1, which facilitates the extraction of lactate from extracellular fluid, and MCT 4 that facilitates the next efflux of lactate. Lactate is the metabolic fuel of muscles, but excessive accumulation of lactate poisons the muscle. Equine performances can be improved when the glycolytic muscle enhances its ability to remove lactate from within contracting cells. This is significant because intracellular lactate accumulation does have a negative effect on muscle acidosis and fatigue process.
By contrast, enhanced rates of lactate removal are associated with a slowing of muscle fatigue and improved performance.
“What is important is that these characteristics are enhanced with appropriated training.” (Michael I. Linger, Lactate: metabolic fuel or poison for racehorses? 2011)
Motion is a primary component of the horse’s re-education. However, exactly like lactate, which is the greatest metabolic fuel for muscles’ work, but can also be a poison, motion is the greatest asset of the horse’s re-education when proper, but is also the main cause of injuries when improper. Proper motion is not defined by judging standards since judging standards rely on antiquated knowledge. Efficient body coordination is not achieved by conventional equestrian education since equestrian education has not evolved with scientific knowledge.
In 1992, Nancy Dueuel recorded world-class dressage horses along the Atlanta Olympic dressage ring. The recording was made on high-speed camera and consequently played back in slow motion for kinematics studies. Horses who should have dominated the difficulty level of the piaffe, adding their style and charisma to the execution of the performances were actually showing struggle and suffering. Recently, the horse who was literally limping on three legs in the dressage ring was awarded a score of 69.8 or 9%.
In the hunter ring, the rate of injuries is now reaching an alarming level. Hocks are regularly injected because the root cause of cartilage alteration is not addressed. Walter et al have demonstrated that osteoarthritis is largely due to abnormal stresses on the bone structure rather than the cartilage.
Osteoarthritis onset and propagation is mediated largely through biomechanical forces acting across the joint.
Not only can proper limb kinematics slow down the evolution of damages such as osteoarthritis, proper locomotion also stimulates preventive bone remodeling.
“In response to overload exercise in cancellous bones, damage is prevented rather than cured through infilling the prior marrow space compartment.” (Alan Boyde)
In the study, the term overload should not be interpreted as excessive stress but rather increased stress that remains within normal physiological limits. One can refer to such overload as good stress.
Improper motion is the outcome of training techniques, riding principles, and judging standards ill adapted to the horse’s biological mechanism. As early as the 15th century, Leonardo da Vinci warned against bookish prejudices:
“Experience never errs; it is only your judgment that errs in promising itself results that are not caused by your experiments.” (Leonardo da Vinci, 1452-1519)
Bookish prejudices are preventing riders, trainers and judges from exploring beyond established beliefs. Bookish prejudices remain today the major cause of horses’ injuries. Pedantic prejudices are the reason why riders and trainers are returning to the same riding technique and training scale once therapies have taken care of the horse’s soreness or injury.
The aim of this journey is to explore the missing link, the faculty to extend into locomotion the benefices of static therapies.
If we look for instance at a simple joint from a superficial perspective down to a macroscopic view, we take conscience of layers being all part of the efficiency and soundness of the horse’s locomotion and performances. Many dismiss knowledge saying that they “feel”. The problem is that “feeling” is just a perception and as long as feeling is not completed in the brain by a sound and updated picture of the way the horse’s physique effectively functions, feeling often leads to drastic misconceptions. The ones who feel but don’t know simply don’t know what they feel.
We take a structure that is very common in the horse’s body and referred to as tensegrity structure.
A tensegrity structure is characterized by use of continuous tension and local compression. The simple joint illustrated in this diagram (fully explained above), is stabilized by continuous balance between tension and compression elements. The (C) on the bone means compression and the (T) on the ligament means tension.
As we look deeper with a microscope, (two middle views), we can see contractile cells and local regions of tensionally stiffened ligaments extracellular matrix.
At a deeper scale, contractile microfilaments and microtubules act as balanced tension and compression elements respectively
An element placed under tension at one size of scale, can act to resist compression on a smaller size scale. Quite obviously, we don’t have any direct control of such structures and function. It is how, down to microscopic level, bones and ligaments stabilize a joint under stress. Stress is mainly weight and as a rider we can easily alter proper functioning of such structure, applying techniques that are increasing the weight on the forelegs, such as lowering of the neck.
We have explained earlier that often, damages in the cartilage of the joints commence by microfracture, or other damages in the subchondral bones. You start to understand now how such damage can be created, believing in the superficial effects of riding and training techniques but ignoring deeper damages. It is this knowledge that leads us to move away from riding and training techniques that increase the load on the forelegs.
Another major source of deep damage is the erroneous concept of rushing the horse forward. Trainers will tell you that “more forward” is what you need to do in order to win in the show ring. It is effectively a misconception promoted by judging standards, but rushing the horse faster than the horse’s natural cadence alters the proper functioning of the horse’s structures from superficial down to macroscopic level.
“Because the muscle is composed of both muscle fibers and tendinous materials, all of these structures must be collectively ‘tuned’ to the spring properties of the muscle-tendon system to store and recover elastic strain energy during locomotion.” (Paul C. LaStayo, PT, PhD. John M. Woolf, PT, MS, ATC. Michael D. Lewek, PT. Lynn Snyde-Mackler, PT, ScD. Trugo Relch, BS. Stan L. Lindstedt, PhD. Eccentric Muscle Contractions: Their contribution to injury, prevention, rehabilitation, and sport. Journal of Orthopaedic & sports physical therapy. 557-571. Volume 33, No.10, October 2003)
Each horse is designed to “vibrate” at its own frequency, which is its natural cadence. Rushing the horse faster than its natural cadence alters the whole structure at all size scales. Ignorance denies new knowledge because it exposes the thickness of their ignorance but it exposes also your horse to the damages resulting from their ignorance. The rider is ultimately the horse’s sole protection and the horse’s ability to perform at its full potential and remain sound depends largely on the rider’s knowledge.