The Muscular System · 2018-06-18 · Lecture – The Muscular System Return to Table of Contents Function of Muscles The muscular system of the horse forms the largest tissue mass

Lecture – The Muscular System

Return to Table of Contents

The Muscular System

EQS 110



Table of Contents

Function of Muscles ...................................................................................................................... 3

Types of Muscle Tissues ............................................................................................................... 3

Smooth Muscle ............................................................................................................................ 3

Cardiac Muscle ............................................................................................................................ 3

Skeletal Muscle ........................................................................................................................... 4

Deep & Superficial ........................................................................................................................ 4

Muscle Movement ......................................................................................................................... 5

Muscle Fiber Types ..................................................................................................................... 5

Slow Twitch ........................................................................................................................ 5

Fast Twitch.......................................................................................................................... 5

Flexors & Extensors .................................................................................................................... 6

Sphincters .................................................................................................................................... 6

Cutaneous .................................................................................................................................... 6

Management of Muscles – Tying Up ........................................................................................... 7

What is Tying Up? ...................................................................................................................... 7

Types of Tying Up ...................................................................................................................... 7

Signs of Tying Up ....................................................................................................................... 8

Causes.......................................................................................................................................... 8

Treatment of Tying Up ................................................................................................................ 8

Management of Tying Up ........................................................................................................... 9

Dietary Management ..................................................................................................................... 9

Exercise Management ................................................................................................................... 9

Effect on Performance ................................................................................................................. 9

Self-Knowledge Checks .............................................................................................................. 10

Answers ..................................................................................................................................... 11

Glossary ....................................................................................................................................... 12

Click on the different sections

of the table of contents to

jump through this document



Function of Muscles

The muscular system of the horse forms the largest tissue

mass in the body and is responsible for controlling every

aspect of movement, both internal and external. In addition

to movement, muscles also function to:

Produce heat

Maintain posture

Types of Muscle Tissues

The horse’s muscular system can be broken down into three types of tissue:

Smooth

Cardiac

Skeletal

We will look at each of these muscle types individually, placing the largest focus on the last

category, skeletal muscle.

Smooth Muscle

Smooth muscle is an involuntary muscle which functions

automatically. It surrounds all internal tissues and organs

and responds to stimuli from the nervous system. Smooth

muscle can be found in areas of the body that do not

require conscious control, such as the urinary tract and

digestive system.

Cardiac Muscle

Cardiac muscle is also an involuntary muscle but its function is to

coordinate the propulsion of blood in and out of the heart. With the

heart beating around 100,000 times a day throughout a horse’s lifetime,

this muscle is fatigue resistant. For a racehorse, proper development of

cardiac muscle through training is crucial for performance!



Skeletal Muscle

Skeletal muscle is a voluntary muscle responsible for external

movement as well as:

Maintaining posture

Controlling range of movement

Protecting from trauma

Thermoregulation

A horse has over 700 different skeletal muscles! Muscles are

able to produce movement via tendons, a type of connective

tissue that attaches muscles to bones. Muscles are then signaled to contract via nerve impulses.

Relaxation occurs when the nerve impulses cease. Due to their immense role in creating movement,

we will take a closer look at the categorization and functions of skeletal muscle.

Deep & Superficial

Skeletal muscles can be categorized based on their depth of placement in the body. For

purposes of this course, you will not be required to know the names of each individual deep

and superficial muscle.

Deep Muscles

Deep muscles are for posture and stability. They attach

directly to the bone and are located close to the joints.

Superficial Muscles

Superficial muscles are located between the deep muscles and the skin. Although they vary

in size and shape, they are generally known as movement muscles and are greatly responsible

for a horse’s athletic performance. As movement muscles, superficial muscles can become

tense and sore – no different than a human athlete. This, in turn, can affect performance as

well as mental attitude. Since these muscles are the outermost layer, they can be easily felt for

tension, heat, and swelling and be readily influenced by complementary therapies, such as

massage, magnetic therapy, and stretching.



Muscle Movement

Muscle is made up of thousands of fascicles, which are bundles of fibers running parallel to each

other – this is what gives muscle its striated appearance. Skeletal muscle, which is the muscle

category primarily responsible for movement, can consist of two muscle fiber types. The type

and proportion of muscle fibers a horse has can determine what activity he/she may excel at.

Slow Twitch

Slow twitch, also called Type I, are muscle fibers that contract

slowly for long periods of time in the presence of oxygen; they use

aerobic metabolism to produce the energy needed for muscle

contraction. Since these are “slow-burning” muscle fibers, they do

not create toxic end products of muscle contraction, such as

lactate, which can cause a horse to cramp. This makes them ideal

for non-strenuous work.

Fast Twitch

Fast twitch, also called Type II, are powerful and fast

contracting muscle fibers that produce quick energy without

the presence of oxygen; they use anaerobic metabolism to

produce the energy needed for muscle contraction. While

these muscle fibers produce speed, they also tire quickly and

create a by-product during muscular contraction known as

lactic acid. Lactic acid can result in cramping if allowed to

build up in the body.

Every horse has a mix of fast and slow twitch muscle fibers. The proportions are determined by

breed and genetics. Horses with a higher proportion of slow twitch fibers have more stamina,

tire less easily, and make good endurance or leisure horses. Those with a higher proportion of

fast twitch fibers have less stamina but more explosive energy. Arabians are a breed of horse

that show higher proportions of slow twitch muscle fibers while Quarter Horses and

Thoroughbreds show higher levels of fast twitch muscle fibers. Appropriate training can have an

immense impact on performance and bring each type of horse to its peak level of fitness. For

example, a Thoroughbred must have stamina as well as speed – adapting the muscular system

to exercise can improve the muscle’s ability to store oxygen and increase its aerobic and

anaerobic capacity. While training and conditioning can have a significant impact on the

muscular system, it cannot entirely rewrite what type of muscle fibers the horse was given; this

is why we don’t see certain breeds racing competitively!



Flexors & Extensors

Flexors and extensors are a group of muscles that lay on the limbs to

either decrease or increase the angle. Flexor muscles lay on the back

of the limb to decrease the angle (axes of the limb are brought closer

together) – think about when you flex your arm, you are bringing the

axes of your bone closer together. Extensor muscles do the opposite;

they lay on the front of the limb to increase the angle (axes of the

limb are brought farther apart).

Sphincters

A sphincter is a ringlike muscle that contracts (closes)

a passage or opening. Commonly found in the

digestive tract, the strength of the lower esophageal

sphincter is one reason why a horse cannot vomit!

Cutaneous

Cutaneous muscles allow for movement of the skin. Horses

use this muscle to twitch and remove irritants like flies.

Flexing

Extending



Management of Muscles – Tying Up Taken in part from “What is Tying up in Horses” by Tania Cubitt, PhD, January 17th, 2004

Muscle disorders are a frequent cause of poor performance in horses, and for a racehorse, can be performance-limiting or even career ending. Tying up, also referred to as Exertional Rhabdomyolysis, Azoturia, or Monday Morning Sickness, is the most common muscle disorder seen in the athletic horse. Understanding this disorder is vital if you wish to be involved in the care and training of horses, no matter the discipline.

What is Tying Up?

The scientific name for Tying up is rhabdomyolysis, which simply translated means muscle (myo) breakdown (lysis). The causes of Tying up vary but the result is the same, muscle cramping. In this condition, there is a massive contraction of the muscle groups along the back and rump of the horse. The muscles contract and do not relax. The horse will appear to be almost nailed to the floor in the hindquarters and unwilling to move. The horse will appear to be significant pain and show signs of distress, including increased heart rate and sweating. If you place your hands along the muscles on either side of the spine on a horse that has tied up, they feel rock hard. While cases will range in severity, horses that are showing signs of tying up require immediate medical attention from a veterinarian.

Types of Tying Up

Horses experiencing tying up can be placed in one of two broad categories:

1. Sporadic (acute) exertional rhabdomyolysis – this classification applies to horses which, on rare occasion, experiencing an episode of generalized tying up. This will generally involve muscle stiffness and cramps

2. Chronic exertional rhabdomyolysis – when a horse experiences repeated episodes of ER, with the first episode usually occurring at a young age. This type is much more problematic for an athletic horse and can result in irreversible muscle damage



Signs of Tying Up

The signs of tying up vary with the severity of the condition and the speed of onset. In mild cases, the horse’s gait gradually stiffens and he becomes reluctant to move. The muscles are actually cramping and feel very much to the horse like muscle cramps do to human athletes. The large, heavy muscles of the hind legs are most affected, but the triceps muscles above the elbow of the front legs may also appear stiff and painful. Additional signs include sweating, elevated heart and respiratory rate, and dark red/brown urine due to muscle damage. Most cases of tying up are diagnosed by these clinical signs, but bloodwork can be taken to evaluate the muscle enzyme levels, which can help develop a specific treatment plan.

Causes

Horses often tie up when exercise exceeds the horse’s underlying state of training. We may see this occur with young horses when they first go to the track and do too much too soon or with older horses returning from a rest (also called a layoff) and exercising beyond their current level of fitness. Tying up may also occur due to excitability and stress (traveling, breeding, showing). Tying up may also have a nutritional basis, such as an electrolyte imbalance, abnormal carbohydrate metabolism, or mineral/vitamin deficiencies. Unfortunately, for some horses, the cause of Tying up may be unknown. Working with your veterinarian is going to be key in the treatment and management of horses that tie up.

Treatment of Tying Up

Horses showing signs of tying up should cease exercise immediately – do not force a horse to walk if it cannot as this can increase muscle damage. If it is cool, cover the horse, especially its hindquarters with a cooler or blanket to keep warm. Horses that are able to walk should continue to do so unless otherwise directed. Your veterinarian should be contacted but in the meantime, determine if the horse is dehydrated and provide fluids via small frequent sips of water. In order to relax the muscles and allow the horse to move, your veterinarian may need to administer a non-steroidal anti-inflammatory drug (NSAID) and/or a sedative depending on the severity. Horses that suffer from an episode of Tying up should be rested for 3-5 days with a gradual increase in exercise.



Management of Tying Up

Diet and exercise are closely linked to Tying up and the most important preventative strategies are based upon diet and exercise management.

Dietary Management

The most common dietary change made to horses that tie up involves a reduction in grain. High cereal grain diets can overload the normal digestive processes of the small intestine and overflow to the hindgut, which is not meant to digest grain products. Too much grain in the horse’s hindgut can increase lactic acid production, fluctuate blood glucose levels, and increase fluid and electrolytes losses due to increased heat production. Checking the diet for balanced levels of minerals and vitamins will also be key. Incorporating the assistance of an equine nutritionist is beneficial for horses suffering from Tying up.

Exercise Management

An exercise protocol is going to vary horse to horse but several basic principles can help horses that suffer from Tying up:

Consistent, structured program Grading the level of exercise with a slow increase in intensity as fitness develops Following hard work with a slow trot or canter to stimulate the delivery of oxygen and removal

of lactic acid from the muscles Adequate warming up and cooling down procedures

Effect on Performance

There is no cure for horses with chronic forms of Tying up. Severe and recurrent episodes can result in irreversible muscle damage and impact the ability for a horse to perform. Even if a horse does not show repeated bouts of this disorder, the appearance of these signs needs to be taken seriously to not only prevent muscle damage but prevent future episodes. Horses that tie up due to excitability and nervousness will need to managed carefully – avoiding stress and excitement will be key, but that is difficult for a racehorse. Working closely with your veterinarian, as well as an equine nutritionist if needed, will be vital for your horse’s health and success.



Self-Knowledge Checks

1. Muscle that is involuntary and surrounds all

internal tissues and organs is characterized as:

a. Cardiac b. Smooth c. Skeletal

2. Muscles are able to produce movement via

this structure, which attaches muscles to bones

a. Tendon b. Ligament c. Joint d. Fascia

3. Which type of skeletal muscle will be most

readily influenced by therapies such as massage

and stretching?

a. Deep b. Superficial

4. _____ twitch are muscle fibers that contract

slowly for long periods of time in the presence of

oxygen

a. Slow b. Fast

6. A buildup of lactic acid in the body can result in:

a. Heart failure b. Muscle cramping c. Inability to breathe d. Inability to defecate

8. The image below is engaging which group

of muscles?

a. Extensors b. Sphincters c. Flexors d. Cutaneous

9. When a horse twitches his skin to remove an irritant,

like a fly, he is engaging which muscle group?

a. Flexors b. Cutaneous c. Sphincters d. Extensors

10. Severe muscle cramping that involves distress,

inability to move, and increased heart rate is known as:

a. Stocking Up b. Bucked Shins c. Tying Up d. EPM

5. Fast twitch muscles use anaerobic metabolism

to produce quick energy – which statement

correctly describes this process?

a. Fast twitch muscles produce quick energy without oxygen b. Fast twitch muscles produce quick energy with oxygen

7. Appropriate training can improve muscle fiber ability

a. True b. False



Answers

1. Muscle that is involuntary and surrounds all

internal tissues and organs is characterized as:

b. Smooth

Smooth muscle in an involuntary muscle that functions automatically. It surrounds all internal tissues and organs

2. Muscles are able to produce movement via this

structure, which attaches muscles to bones

a. Tendon

Tendons are a connective tissue that attaches muscles to bones, allowing for movement

3. Which type of skeletal muscle will be most readily

influenced by therapies such as massage and stretching?

b. Superficial

Superficial skeletal muscles are the outermost layer and can easily felt for tension, heat, and swelling. As a result, complementary therapies, such as massage and stretching, can help relax them

4. _____ twitch are muscle fibers that contract slowly for

long periods of time in the presence of oxygen

a. Slow

Slow twitch, also called Type I, are muscle fibers that contract slowly for long periods of time in the presence of oxygen

5. Fast twitch muscles use anaerobic metabolism to

produce quick energy – which statement correctly

describes this process?

a. Fast twitch muscles produce quick energy without oxygen

Anaerobic metabolism is not dependent on oxygen to break down fuel stores. This means that fast twitch muscles produce quick energy without the presence of oxygen

6. A buildup of lactic acid in the body can result in:

b. Muscle Cramping

Lactic acid is a by-product of fast twitch muscular contraction. When allowed to build up in the body, it can result in muscle cramping

7. Appropriate training can improve muscle fiber ability

a. True

Appropriate training and conditioning can help adapt the muscular system to physical demands by improving the ability of the muscle fibers to store oxygen or increasing its aerobic and anaerobic capacity. Training cannot rewrite the genetics and breed of a horse, which is how proportions of muscle fiber is determined

8. The image below is engaging which group of muscles?

c. Flexors

In the presented image, the axes of the hindlimb are being brought closer together. When the axes of a limb are brought closer together, the flexor muscles are being engaged

9. When a horse twitches his skin to remove an irritant,

like a fly, he is engaging which muscle group?

b. Cutaneous

Cutaneous muscles allow for movement of the skin. Horses use these muscles to twitch and remove irritants like flies

10. Severe muscle cramping that involves distress,

inability to move, and increased heart rate is known as:

c. Tying Up

Tying up is a muscular disorder characterized by severe muscle cramping, distress, inability to move, and increased heart rate



Glossary

Acute – Sudden and severe, quick onset

Aerobic Metabolism – Is dependent on oxygen to break down fuel stores – inhaled oxygen

during aerobic exercise is carried to the muscles and liver to metabolize (utilize) carbohydrates

and fats for the production of ATP, the energy source for muscle contraction. Exercise is

classified as aerobic if the heart rate is less than 150 beats per minute. The waste products of

aerobic metabolism are carbon dioxide, water, and heat

Anaerobic Metabolism – Is not dependent on oxygen to break down fuel stores, provides a

rapid means of producing a limited supply of energy during anaerobic exercise. Exercise is

classified as anaerobic if the heart rate is greater than 150 beats per minute. In the absence of

oxygen, only carbohydrates can be metabolized for ATP production and the waste products of

anaerobic metabolism are heat and lactic acid

Cardiac Muscle – An involuntary muscle tissue that functions to coordinate the propulsion of

blood in and out of the heart

Chronic – Long term

Cutaneous – A muscle group that allows for the movement of the skin

Deep Muscles – A classification of skeletal muscle that provides the horse with posture and

stability

Extensors – A muscle group that lays on the front of the limb to allow for extension (increase

limb angle)

Fast Twitch – A type of muscle fiber that creates quick energy via anaerobic metabolism

Flexors – A muscle group that lays on the back of the limb to allow for flexion (decrease limb

angle)

Involuntary – Do not have conscious control over

Lactic Acid – A waste product of fast twitch muscle fiber use and anaerobic metabolism, can

result in cramping if allowed to build up

Layoff – A period of rest, may include turnout and/or stall rest

Skeletal Muscle – A voluntary muscle tissue responsible for the production and control of

external movement, maintaining posture, and thermoregulation

Slow Twitch – A type of muscle fiber that that contracts slowly for long periods via aerobic

metabolism

Smooth Muscle – An involuntary muscle tissue that surrounds all internal tissues and organs

Sphincter – A muscle group that contracts (closes) a passage or opening



Superficial – A classification of skeletal muscle found between deep muscles and the skin,

generally known as movement muscles

Tendon – A type of connective tissue that connects muscle to bone

Tying Up – A muscular disorder that results in severe cramping of the large hindquarter muscles

Voluntary – Can be consciously controlled

Documents

The Muscular System · 2018-06-18 · Lecture – The Muscular System Return to Table of Contents Function of Muscles The muscular system of the horse forms the largest tissue mass