Far surpassing all other tissues in sheer mass, muscles account for a remarkable 50% of your horse’s body weight (and that excludes fascinating fascia that connects and coordinates your horse’s muscles) —a true testament to the many vital roles they play in the body’s ability to operate.
Let’s learn about the 10 important functions muscles serve in your horse’s body
1. Movement
Movement is often the function we think of first when considering what muscles do for our horse.
Exploring muscle structure, arrangement, and function (a study known as Myology), helps us understand how muscles work and how they impact your horse’s performance and well-being.
Skeletal muscles create movement and locomotion through contraction in response to nerve signals. They pull on the structures they’re attached to, causing body parts to move and joints to flex, extend, rotate. Skeletal muscles are under your horse’s conscious, voluntary control.
A whole skeletal muscle is considered an organ of the muscular system. It consists of 100s-1000s of muscle fibers, nerve tissue, blood and vascular tissue and connective tissues.
Skeletal muscle is enveloped in a connective tissue framework at three levels. Each individual muscle fiber (cell) is covered by endomysium, groups of muscle fibers are bundled together by perimysium and called fascicles, and the entire muscle is covered by epimysium. These coverings provide support and protection for the fragile muscle cells, enabling them to withstand the forces of contraction; they also provide pathways for the passage of blood vessels and nerves.
These protective coverings extend beyond the fleshy part of the muscle and merge to form tendons (fibrous, cord-like connective tissue) and aponeuroses (broad sheet-like connective tissues) and attach the muscles to bones, fascia, and other structures.
Skeletal muscles have two or more points of attachment. One side attaches to one or more relatively stationary or fixed parts of the skeleton, while the other side attaches to one or more points of bone, fascia, or skin farther away from the center of the body and with greater mobility. Muscles contract to bring the two ends of the muscle closer together, drawing the more mobile end towards the more stationary end, causing movement at the joint(s) between the attachment points. The length and arrangement of muscle fascicles determine the muscle’s range of motion and its ability to generate force. Longer fascicles tend to have more range of motion, while shorter fascicles can generate more force.
Size and location also play a role in muscular mechanics. As a general rule, large muscles responsible for generating power and big, gymnastic movements are located farther away from the joints, while smaller muscles near the joints are often involved in the more precise, finely-tuned aspects of movement, providing detailed control and stability.
Skeletal muscles typically work in pairs or groups: agonists initiate movement, while antagonists provide the opposing action, aided by surrounding muscles for stability and control. For instance, one set may facilitate flexion, while the other relaxes to support the opposite action—extension—with surrounding muscles supporting smooth, coordinated movements.
Muscles connect to and coordinate with nearby muscles through fascia. These connections form intricate myofascial chains that extend across the horse’s entire body, linking head to toe, overlapping each other, some crossing from one side of the horse to the other, one or more times. Each myofascial chain plays an integral role in shaping posture, carriage, movement and balance within the intricate dynamics of the musculoskeletal system. Myofascial chains, like individual muscles and groups of muscles, also operate in pairs, with one chain of muscles initiating an action such as flexion, and the other relaxing and extending to facilitate and balance the movement, and supported by surrounding, synergistic myofascial chains.
Myofascial chains enhance stability and facilitate efficient energy transfer during each gait and movement. Individual muscles often contribute more than one myofascial chain, highlighting the interconnected nature of the musculoskeletal system and the importance of considering holistic perspectives when understanding movement patterns and addressing issues related to the muscular system. Lost functionality caused by tension, pain, or instability in any muscle will affect entire chains and lead to compensatory movements across the body, limiting stability, mobility, power and performance.
2. Posture
Muscles play a crucial role in stabilizing the skeleton and posture, whether standing still or in motion. Postural muscle tone, known as “tonus,” is the subtle tension these muscles maintain to uphold the horse’s body position. Deep muscles and those near joints often serve as postural muscles, maintaining vital low-level activity for stationary positions, increasing tension as to needed to meet the demands of different position and movements. These postural muscles have a high number of nerve endings that are uniquely sensitive to postural alignment.
Strong, well balanced postural muscles stabilize the skeleton and support optimal weight distribution, both of which are essential for sound biomechanics and athletic performance. They provide a foundation for the horse to move efficiently, with power and coordinated, controlled movements. This is particularly important for disciplines that require precision, agility, and responsiveness.
Furthermore, correct postural muscles contribute to your horse’s overall well-being and are fundamentally important for the horse’s health, performance, and longevity. They help prevent injuries by supporting the body in a way that minimizes stress on joints, organs, and tissues.
Poor muscle tone or excessive or unbalanced tension in postural muscles will result in poor posture, poor biomechanics, increased stress on joints, organs and other tissues, musculoskeletal issues, pain and poor performance.
3. Joint Stability and Protection
Muscles play a vital role in stabilizing and supporting joints, ensuring proper alignment, correct spacing between structures (for example, kissing spines) and actively protecting against excessive torque, over-flexion, overextension and other mechanical stresses. Muscles near joints enhance stability, strength, and control, optimizing mechanics around the joint. Muscles and their tendons also provide joint protection by effectively absorbing and dispersing forces away from and around the joints, safeguarding them from undue stress and damage.
Robust, supple, balanced muscles are essential for healthy joint biomechanics. When stabilizing muscles are compromised and can’t perform their role, nearby muscles may try to compensate, disrupting their own functions in the process as well as compromising the action, safety and wear and tear on the joint.
4. Heat Generation
Muscles generate heat as they contract, playing a vital role in regulating body temperature.
When your horse’s muscles contract, they consume energy. This energy is derived from the breakdown of nutrients, primarily glucose and fatty acids, in a process called cellular respiration. As muscles break down these nutrients to produce energy, a significant portion of the energy is released as heat. The more intense the muscle activity, the more heat is generated.
Body temperature regulation, which must remain fairly stable for optimal function, is a dynamic process that involves a balance between heat production and heat dissipation. Muscles contribute to this balance by adjusting their activity level to either generate more heat (as in shivering when cold*) or reduce heat production (as in sweating and relaxing muscles when hot).
* Please note that shivering for heat generation is the body’s last resort for creating enough heat to keep its core temperature at a safe level. It uses a great deal of energy, primarily from the breakdown of stored glycogen and the burning of calories, and will lead to tight, sore, tired muscles due to the repetitive, involuntary muscle contractions. The body will prioritize maintaining core temperature over these concerns, but it’s still a signal that the environment is posing a threat to your horse’s overall health.
5. Breathing
In horses, the diaphragm’s primary function is to facilitate inhalation. When the diaphragm contracts, it moves downward, creating a vacuum in the chest cavity that draws air into the lungs. (see: All Muscles Used During Breating)
Exhalation, on the other hand, is primarily a passive process, at least at rest. Once the diaphragm relaxes and returns to its dome-shaped resting position, it reduces the space in the chest cavity. This reduction in space increases the pressure inside the lungs, causing air to be expelled passively through the trachea and out of the nostrils. The diaphragm doesn’t actively contract to push air out as it does in humans.
During exercise or periods of heavy breathing, horses rely on other muscles for breathing support. Muscles like the external Intercostal muscles, Serratus Ventralis and Serratus Dorsalis, and smaller muscles in the neck, chest, and nose contribute to efficient inhalation.
To exhale, horses primarily rely on their abdominal muscles, with assistance from the internal intercostal muscles that contribute by compressing the ribcage during exhalation. When your horse breathes heavily due to exertion, its abdominal muscles contract forcefully, pushing the diaphragm upward, expelling the air from the lungs, enhancing respiratory efficiency. These abdominal contractions can be part of the canter or gallop stride or can occur as a separate action. Given their substantial size, horses require a considerable amount of muscular strength to maintain proper ventilation.
6. Circulation
The heart muscle pumps blood, while smaller muscles in blood vessels regulate blood flow. These cardiac muscles are under the control of your horse’s autonomic system (ANS), a division of the peripheral nervous system that controls involuntary bodily functions such as heart rate, digestion, respiratory rate, etc.
Cardiac muscle of the heart contracts rhythmically to pump oxygen-rich blood to all parts of the body through arteries.
Smaller muscles, located within the walls of blood vessels like arteries and arterioles, help regulate blood flow and pressure. These vascular muscles can constrict or dilate to control the diameter of the blood vessels. Constriction narrows the vessel and reduces blood flow, while dilation widens the vessel, allowing more blood to pass through. Together, the coordinated action of the heart and these smaller vascular muscles ensures that blood is efficiently distributed to meet the body’s varying oxygen and nutrient demands. Tight muscles and knots can interfere with blood flow so it’s very important to maintain correct muscle tension in the whole body.
Skeletal muscles, which are under your horse’s conscious control, such as those in their necks and legs, contract and relax during activities like walking, galloping, or grazing, also play a role in blood circulation through a mechanism known as the muscle pump or venous pump. When muscles contract, they squeeze nearby veins, effectively pushing blood toward the heart. This action is particularly important in the extremities where the force of gravity makes it more challenging for blood to return to the heart. The rhythmic squeezing of muscle contractions propel blood upward, assisting in venous return to the heart. Veins are equipped with one-way valves that prevent backward blood flow, ensuring it travels in the intended direction.
Horses get additional circulation assistance from every step they take: When the foot is placed on the ground, increased pressure and changes in the shape of the digital cushion and frog compress the veins in the foot and force blood from the foot to the leg. Lifting the foot then relieves this compression, allowing blood to flow back into the veins. Essentially, the movement of these structures in the hoof functions as a pump.
The both the muscle and hoof pumping mechanisms are essential for maintaining healthy circulation and preventing blood pooling in the extremities. They highlight the interconnected nature of the muscular and circulatory systems.
7. Digestive Process
Nimble lips and tongue draw food and water into the mouth.
Muscles in the jaw and face such as the masseter, pterygoid muscles, and temporal muscle are involved in mastication, breaking down food into smaller particles, and with the help of the tongue muscles which move the food around the mouth, mixing the food with saliva, for better digestion.
The muscles of the pharynx and esophagus coordinate to propel chewed food toward the stomach through a process called deglutition or swallowing.
The stomach has smooth muscles that contract to mix food with digestive juices, forming a semi-liquid mixture called chyme.
Smooth muscles in the small intestine move chyme along, in a process called peristalsis, allowing for further digestion and absorption of nutrients.
In the cecum and colon, powerful contractions aid in microbial fermentation of fibrous material, extracting additional nutrients.
Finally, muscles in the rectum facilitate the expulsion of indigestible material from the body through the anus during defecation and muscles in the pelvic region and the urethra play a role in the process in the eliminating liquid waste from the body through urination.
8. Communication
Horses predominantly communicate through the art of body language, movement and facial expressions, fine tuning multiple muscles to convey a rich tapestry of thoughts and emotions – just imagine how difficult it would be for a horse to communicate clearly if its ear muscles were paralyzed. To vocalize they use muscles to adjust breathing patterns to create different sounds and the position of the lips, tongue, and nostrils to influence the characteristics of the vocalization. Muscles in and around the larynx control the tension and movement of the vocal cords to create variations in pitch and intensity.
9. Protection
Muscles play a important role in shielding delicate structures, safeguarding internal organs from external forces that could jeopardize the body’s well-being.
Muscles serve a natural “cushion,” absorbing impacts and dispersing concussion, preventing potential injuries and reducing wear and tear.
Muscle splinting, a protective mechanism, involves the involuntary contraction of muscles around an injured area—a natural response to shield the injury. Its purpose is to limit movement in the affected region, minimizing the risk of additional damage or pain. Prolonged or excessive muscle splinting can result in issues like stiffness and reduced range of motion. Striking a balance between self-protection and therapeutic massage and movement is essential for success healing.
Muscles support and safeguard internal organs during dynamic activities such as trotting, galloping, jumping, and sudden movements. By contracting and generating tension in the fascia, they stabilize and prevent displacement, shielding organs from excessive movement.
Muscles contribute to the immune response by adjusting during inflammation, aiding in isolating injured or infected areas. When tissues are affected, immune cells rush to the scene, and surrounding muscles can adapt by contracting to restrict pathogen movement and isolate the affected area.
Muscles possess a remarkable ability for reflexive contraction, functioning independently of the brain to safeguard the body. For instance, in the withdrawal reflex, rapid muscle contractions move a body part away from danger, minimizing the risk of injury. The startle reflex in horses, also known as the “startle response” or “flight response,” is an instinctive reaction to sudden or unexpected stimuli. When a horse perceives a potential threat, it may respond by quickly bracing its muscles, making a sudden jump, or rapidly changing its posture. This reflex is an evolutionary adaptation that enhances the horse’s ability to react swiftly and move away from perceived dangers, contributing to its survival in the wild and is commonly behavior observed in domestic horses.
The stretch reflex rapidly contracts muscles in response to sudden or excessive stretches, preventing structural damage from overextension. Golgi tendon organs in tendons trigger reflexive muscle relaxation, acting as a safeguard against potential injuries.
Additional reflexes in horses, like sneezing and coughing, expel irritants, safeguarding the respiratory system. When triggered by irritation in the nasal passages or respiratory system, the body responds by forcefully expelling air to clear these irritants. Muscles engaged in these reflexes include the diaphragm, neck, stomach muscles, and various facial muscles and back and chest muscles for stabilization.
Digestive peristalsis, propelled by rhythmic muscle contractions, aids timely waste removal, preventing harmful substances from lingering in the digestive tract. This reduces the risk of these materials reaching deeper tissues or causing issues in the digestive system.
These protective mechanisms and reflexes showcase the intricate ways in which muscles coordinate with other systems to safeguard the body and maintain optimal function.
10. Sensory Information
Sight, hearing, smell, taste, touch, and feel enable horses to perceive and interact safely with their environment.
Specialized receptors within your horse’s muscles relay essential information to the brain, detailing muscle length, rate of change in muscle length (velocity), tension, location, temperature, and, in some cases, pain or discomfort. This comprehensive feedback provides your horse with detailed awareness of where its body in space, what its body is doing in space and allows it to monitor and minimize potential stresses and strains. This feedback allows your horse to execute movements with precision and accuracy, to navigate its environment safely and protect itself from injury or over strain.
Muscles control the movement of the eyes and head, allowing your horse to focus on his surroundings, muscles in and around the ears allow horses to swivel, tilt and shape their ears to detect and focus on sounds from different directions, muscles enable the breathing in and channeling of scents, movement of the tongue helps distribute food to the taste buds, allowing the horse to sense flavors and detect dangerous or unpleasant substances in their foods and muscles help provide feedback to the brain about the pressure, texture, and temperature of objects they touch, to provide tactile perception.
Bonus
Pumping Lymph
When blood circulates through tiny blood vessels called capillaries, some of the plasma, along with oxygen, nutrients, white blood cells and hormones, is pushed out through the capillary walls due to blood pressure. This extracellular fluid, now called interstitial fluid, bathes the cells in the surrounding tissues, delivering essential substances and facilitating waste removal. From there, interstitial fluid flows into lymphatic vessels where it becomes lymph. Lymph then travels along a network of lymph vessels, transporting waste products, cellular debris, and pathogens away from tissues to be processed and eliminated from the body. Cleansed lymph then rejoins the bloodstream to begin the cycle again. This continuous process is essential for sustaining a healthy immune system, promoting overall tissue health, eliminating waste products, maintaining correct fluid balance, and preventing the buildup of excess fluids in tissues that can result in swelling or edema.
Unlike the circulatory system and its heart, the lymphatic system lacks a central pump. Instead, voluntary skeletal muscle and involuntary smooth muscles within the lymphatic vessels work together to ensure efficient lymph circulation.
During activities like grazing, walking, or galloping, skeletal muscles, such as those in the back, neck, legs, contract and relax, exerting pressure on nearby lymphatic vessels. This pressure acts as a pump, assisting the movement of lymph fluid into the lymphatic vessels and along their pathways.
Simultaneously, a thin layer of smooth muscles within the lymphatic vessels contract rhythmically, propelling lymph through a network of vessels, filtering nodes, and one-way valves, ensuring the unidirectional flow of lymph toward the heart. The combined action of skeletal muscles and the smooth muscles within the lymphatic vessels ensures efficient circulation of lymph fluid throughout the body.
Conclusion
While we primarily think of muscle as relating to movement and locomotion, muscle actually serves a multitude of irreplaceable roles in your horse’s body, impacting literally every aspect of their life. Make sure that you are taking the very best care of your horse by booking regular massage with myofascial release sessions.
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