Introduction to the Muscular System

There are more than six hundred muscles within the human body and more than 430 are voluntary muscles. Muscles are responsible for a great variety of functions, including body motion, strength, posture, heat production, and much more. Muscle is composed of approximately 75 percent water, 20 percent protein, and 5 percent salts and other chemicals.

Types of Muscle Tissue

Skeletal Muscle

Skeletal muscles form the muscles of the arms, legs, chest, back, neck, and head. They are primarily responsible for body movements. These tissues are voluntary because they are under conscious control.

The skeletal muscles also have other important functions, including the ability to increase basal metabolic rates (BMR), store energy, add body strength, and improve body appearance. By increasing muscle size and strength, bones simultaneously get stronger and denser. All the skeletal muscles are attached to the bones by connective tissues called tendons.

Smooth Muscle

Smooth muscle, also called visceral muscles, help to form the walls of certain internal organs, such as the esophagus, the stomach, the intestines, and blood vessels. These tissues are involuntary because they are not considered to be under conscious control.

Cardiac Muscle

Cardiac muscle is composed of involuntary muscle tissues that form the walls of the heart muscle. These tissues are involuntary because they are not considered to be under conscious control.

Types of Skeletal Muscle Fiber

Fast- and slow-twitch muscle fibers (cells) are only present in the skeletal muscles.

Fast-twitch White Muscle Fiber

Also called Type 2 muscle fiber, this type of fiber is good for anaerobic activity, such as weight lifting, and is characterized by its fast speed of contraction and its high capacity for anaerobic glycolysis.

People with greater percentages of fast-twitch fiber have more strength for anaerobic activity. These people also develop muscle strength and size faster than those with less fast-twitch fiber.

Professional-level power athletes, such as power weight lifters, have a fast-twitch fiber distribution of approximately 60–90 percent in the muscles used for their sport.

Slow-twitch Red Muscle Fiber

Also called Type 1 muscle fiber, this type of fiber is good for aerobic activity, such as running, and is characterized by its slow speed of contraction and a high capacity for aerobic glycolysis.

People with greater percentages of slow-twitch fiber have more endurance for aerobic activity.

Professional-level endurance athletes, such as cross-country skiers and runners, have a slow-twitch fiber distribution of approximately 60–90 percent in the muscles used for their sport.

Distribution of Muscle Fiber

Muscle fiber distribution is entirely genetic. Training will not change one fiber type to another fiber type. Male muscle tissue is not any stronger than female muscle tissue. It’s just that men usually have more muscle tissue.

A male fast-twitch fiber is no different from a female fast-twitch fiber. Also, male slow-twitch fiber is no different from female slow-twitch fiber.

Muscle Fiber Composition and Function

Muscles are composed of large numbers of muscle fibers (sometimes referred to as muscle cells) that have the following components:


The structure in a cell that contains the chromosomes. The nucleus has a membrane around it and is where RNA is made from the DNA in the chromosomes.


The plasma membrane of skeletal muscle (and cardiac muscle) cells.


The sites of aerobic ATP energy production. ATP, or adenosine triphosphate is a high-energy phosphate molecule that is necessary to supply energy for cell function. 

It is stored in the muscles and produced both aerobically and anaerobically. The sites of anaerobic ATP energy production are inside the cells but outside the mitochondria.


Strands of contractile proteins situated throughout the length of a muscle fiber. Though other proteins are present in a myofibril, there are only two types of contractile proteins:

  • Actin
  • Myosin

These proteins run through all the sarcomeres (repeating units of muscle fibers along the length of the muscle cell) that are necessary for muscle contraction. 

Myofibrils increase in number and size with strength training. Sarcomeres increase in number with strength training.

Sliding Filament Theory

This theory states that there must be an interaction between the energy from ATP and the contractile proteins (actin and myosin) and must include a nervous impulse from the Central Nervous System to cause muscles to contract.

Additional Structures of Skeletal Muscle

Interdependent Contracting Skeletal Muscle Fibers

In order for contracting skeletal muscle fibers to be functional, they cannot work as independent or isolated units. It is necessary for them to be bound together.

Every skeletal muscle fiber is bound to its adjacent fiber by the endomysium to form bundles called fascicles. Neighboring fascicles are bound together by another type of connective sheath called the perimysium.

The final outer sheath of the entire muscle group is the epimysium, which is continuous with tendons that attach the muscle to bone.

Muscle Characteristics

Muscle Size


An increase in muscle fiber size resulting in strength gains and muscle size.

A person cannot increase their number of muscle fibers, only the size and strength of their muscle fibers. Muscles get bigger and stronger only by necessity. Strength training is the only way to significantly increase muscle size and strength. 

Regular strength training signals to the muscles that they need to accommodate the burden of lifting heavier weight, and they respond by growing in size and strength. 

Technically, hypertrophy results from an increase in the number and size of myofibrils inside a muscle fiber, resulting in increases to muscle strength and size. Another way to describe hypertrophy is an increase in the amount of the contractile proteins (actin and myosin).


An additional benefit of strength training is an increase in sarcomeres. While most men desire an increase in muscle size and strength, it is not quite as favored by many women due to their concern about developing a “body builder’s” body. 

The fact is that most women cannot develop a high level of muscle size due to their naturally low levels of testosterone.

Best ages for the rate of strength gain are between the ages of ten to twenty, the years of normal growth and development. However, men and women of all ages can increase muscle size and strength with progressive strength training.


An increase in the number of muscle fibers. There is no credible evidence that hyperplasia is possible in humans.


A decrease in muscle size and strength. Causes are inactivity or immobilization resulting from an injury, age, or illness.

Muscle Contraction

Muscles never push; they always pull. In any given action between two bones, one bone is generally in a fixed position, and the other bone has motion. The action is always the result of muscle contraction or, to say it another way, the involved muscle pulling.

For example, when a person is pushing furniture along the floor or performing push-ups, the muscles involved contract concentrically, causing the muscles to shorten, while the muscle fibers simultaneously contract.

Muscle Force

When a skeletal muscle fiber contracts, it creates force. It functions on an all or none principle. This means that it exerts its maximum force automatically. It cannot regulate the force it produces, as can cardiac muscle fiber.

The force a single muscle fiber creates during contraction is directly related to its size.

Larger fiber means greater force. The amount of force an entire muscle creates during contraction is directly related to the size of the fibers within the muscle and the number of fibers within the muscle that contract simultaneously.

Isometric Contraction

In this type of contraction, the applied muscular force is equal to the resistive force (an external force that resists the motion of another force) and the result is no movement.

A typical example of isometric contraction is when a person places his hands in front of his chest and presses the palms together with equal force, resulting in no body movement. Muscle fibers contract, but muscle length remains constant.

Concentric Contraction

In this type of contraction, the applied muscular force is greater than the resistive force and the muscle shortens as its fibers contract to overcome the resistance. A typical example would be the lifting phase (positive phase) of a biceps curl.

Eccentric Contraction

In this type of contraction, the applied muscular force is less than the resistive force and the muscle lengthens as its fibers contract to overcome the resistance. A typical example would be the lowering phase (negative phase) of a biceps curl.

Muscle Attachment

Muscle Attachment Relating to a Limb

  • Proximal: The direction that is toward the attached end of a limb, closest to the head.
  • Distal (a): The direction that is away from the attached end of a limb, furthest from the head.

Muscle Attachment Relating to a Motion

  • Origin: The site of muscle attachment to the fixed bone.
  • Distal (b): The site of muscle attachment to the bone that has motion.

Tendon Insertion

The location of the tendon insertion has an effect on muscle strength. As an example:

Mary and Joan have identical biceps strength, biceps length, and forearm length. However, Mary’s biceps tendon attaches (the insertion point) further down her forearm, and therefore further from her elbow than Joan’s biceps tendon.

The location of Mary’s tendon insertion gives her a biomechanical advantage. It enables her to apply more strength to elbow flexion exercises such as a biceps curl.

Muscle Stabilization

In general, muscles stabilize one joint in order to enable another joint to perform a desired motion.

A typical example of the action of stabilizer muscles is when both the latissimus dorsi (back muscles) and the pectoralis major (chest muscles) contract isometrically, and simultaneously, for the purpose of stabilizing the shoulder joint in order to enable the elbow joint to be flexed when performing a proper form biceps curl.

It should be noted that many isolated exercises (exercises that are properly performed only when there is no motion at other joints, such as the biceps curl, leg curl, and leg extension) require the stabilization of other joints.

Agonist Muscle

Most muscles of the trunk and the extremities exist in opposing pairs. When one muscle of the pair contracts to create a desired motion, that muscle is called the agonist muscle. As this contraction occurs, an opposite muscle of the same pair, called the antagonist muscle (see below), stretches.

For example, when the biceps muscle is contracted, the tricep muscle simultaneously stretches. In this example, the contracting biceps muscle is the agonist, and the stretching triceps muscle is the antagonist.

Antagonist Muscle

The antagonist muscle is always the muscle that opposes the action of the agonist muscle. Additionally, the antagonist muscle is always the muscle that is stretching, while, conversely, the agonist muscle is always contracting.

Synergist Muscles

The combined function of two or more muscles acting together to perform an anatomical movement is referred to as synergistic.

For example, when performing a leg extension exercise, there are four muscles that act together (as synergists) to enable the leg to do this exercise. These four muscles, known collectively as the quadriceps, are the:

  • Rectus femoris
  • Vastus lateralis
  • Vastus medialis
  • Vastus intermedius

Neuromuscular System

The network of nerves that is responsible for the contraction or relaxation of muscles, including the muscle fibers that are connected to them.

Motor Unit

Located within a muscle, it is a single motor nerve, and all the muscle fibers that it stimulates.

Motor units can also exist in groups. Motor units vary in size:

A small motor unit can have a nerve that activates only five to ten muscle fibers. These units are responsible for such delicate actions as blinking, or using a tweezer.

A large motor unit can have a nerve that activates 500–1000 muscle fibers. These units are responsible for such actions as lifting, going up steps, or any activity that requires effort.

Motor units are made of either all fast-twitch muscle fibers, or, all slow-twitch muscle fibers. When fibers of a muscle unit contract, every fiber in that unit contracts simultaneously, and with maximum force (the all or none principle).

Force generated is relative to the amount of motor units that are stimulated to contract simultaneously.

Motor Neuron

A nerve cell that carries motor commands from the central nervous system to the muscles and glands of the body. These commands act as messages that direct the muscles and glands to function in a way that is most beneficial to the body.

Motor Learning Factor

A significant amount of the strength gains that occur in the very early phases of strength training are due to improved neurological factors (motor learning), as opposed to the development of larger muscle fibers.

However, as strength training continues, strength gains are related more and more to the development of larger muscle fibers.

Nervous Inhibition

Composed of both physiological and psychological components, nervous inhibition negatively affects the muscles by inhibiting developmental progress.

From a psychological standpoint, nervous inhibition is a lack of confidence that restricts the individual’s willingness to apply optimal physical performance. From a physiological standpoint, nervous inhibition reduces physical effort resulting in lessened muscle development.

Connective Tissue Types


Connective tissues that attach muscle to bone. Some skeletal muscles are attached to bone with a broad, flat type of tendon known as aponeurosis. A good example of aponeurosis is the wide, flat tendon insertion used by the abdominals.


Connective tissues that attach bone to bone.


Connective tissues that attach muscle to muscle.


A type of connective tissue that acts as an important structural component in many areas of the skeletal system. The most commonly referred to areas for cartilage are the joints. There are three main types of cartilage:

  1. Hyaline cartilage, the most abundant type of cartilage in the body, is found in most of the synovial joints, at the ends of bones. This type of cartilage is a tough, smooth substance that provides a virtually frictionless surface within the joint.
  2. Fibrocartilage is a type of cartilage that is solid and very strong. It makes up the intervertebral discs between the bones of the spine.
  3. Elastic cartilage is the flexible cartilage that is found in various parts of the body such as the outer ear and the epiglottis.

Meniscus refers to the discs found in some of the synovial joints that are made of fibrocartilage. The menisci (the plural of meniscus) are cartilages that are used to divide the joint cavity into two separate cavities.

The menisci are especially important in weight-bearing joints such as the knee because they help to increase stability of the joint and absorb shock.

They also assist in nutrition of the joint by directing the flow of synovial fluid within the joint.

A common knee injury among athletes is the tearing of a meniscus, which is generally referred to as a torn meniscus or torn cartilage.

Stretching and Flexibility

Muscle Stretching vs. Muscle Contraction and Stabilization

Stretching is the elongation of muscle tissue and connective tissue, and it varies greatly from muscle contraction and stabilization.


When muscle fibers are lengthened to increase flexibility.


When muscle fibers contract to create a force that resists an opposing force. Depending on whether the muscles are contracting eccentrically or concentrically, a muscle may either lengthen or shorten during contraction.


When muscle fibers of both the agonist muscle and the antagonist muscle (muscle pairs) contract with equal force to keep a joint from moving.

Flexibility of Joints

Flexibility describes the range of motion of a joint (the distance and direction a joint can move between the flexed position and the extended position).

Flexibility can be improved by applying a force (e.g., a stretch or tension) to a body part by using proper technique in order to overcome the resistive forces from within the joint.

Static flexibility describes the range of motion as it relates to a particular joint, and speed of movement is not an important consideration.

Ballistic (dynamic) flexibility describes the resistance to motion as it relates to a particular joint, and speed of movement is an important consideration.

Flexibility of Connective Tissue

The connective tissues of the body combine two mechanical properties that function to accomplish flexibility:

Elastic Property

Also known as elastic elongation, this is the ability of connective tissue to be elongated and then to recover after the tension has been removed.

Viscous Property

Also known as plastic elongation deformation, this is when the deformation of the elongated connective tissue is permanent, or unrecoverable.

Types of Stretching

Stretching refers to the elongation of muscle tissue or connective tissue. Following are the most popular types of stretches:

Static Stretch

Application of a comfortable stretching force to a muscle or muscle group, which is held for thirty seconds with absolutely no movement once the stretch position has been attained.

This is the most common stretching technique. It is both highly effective and also the safest stretch technique. There are two types of static stretches:

1. Passive Static Stretch

With assistance from a trainer, your own body weight, or a device adds an external force to increase intensity. For example:

For a passive quadriceps stretch, a trainer will bend your knee while pushing the heel of your foot as close as possible to your buttocks.

The trainer will maintain the stretch for thirty seconds. The connective tissue is the section of the quadriceps that is most affected by this stretch and where the stretch has greater permanence.

2. Active Static Stretch

Holding a body part in a stretched position with no assistance other than using the strength of agonist muscles. For example:

For an active hamstring stretch, stand on one leg and hold the opposite leg out directly in front of you, in an extended position, and without any assistance other than from your quadriceps.

The tension of the agonist muscles (quadriceps) in an active stretch helps to relax the antagonist muscles (hamstrings) that are being stretched.

Dynamic (Ballistic) Stretches

These types of stretches are primarily used in athletic drills and use rapid, uncontrolled, bobbing or bouncing motions for short durations. They are designed to activate the stretch reflex.

In these types of stretches, the use of continuous and exaggerated movements that simulate those of a person’s sport or exercise results in improved flexibility for that sport. For example:

  • A runner using extra-long strides to train for competition.
  • A basketball player jumping on and off of an exercise box (also referred to as plyometrics) to target flexibility in the hamstrings and lower back, muscle groups that are used in that sport.

These short-duration, high-force exercises cause muscle spindle activity (a reaction that causes fibers in the muscle tissue to protect against too much stretch).

This results in an increase in muscular reflex contraction to protect against this excessive stretch.

When a muscle contracts (it becomes the agonist), and there is an opposite muscle that stretches (it becomes the antagonist), and it opposes the contraction.

In short, the high forces of dynamic stretching exercises cause greater muscular contraction, and that is why there is greater muscle stretch.

Warning: Ballistic stretching can be dangerous because there is a risk of tearing a muscle or connective tissue. Most therapists, doctors, and trainers consider ballistic stretching to be risky.

Proprioceptive Neuromuscular Facilitation (PNF)

PNF is a method of stretching that is also referred to as the contract/relax method. This technique of stretching is designed to gain a greater degree of stretch in a muscle than conventional techniques by involving teamwork between a client and fitness professional.

The client applies a maximum contraction, while at the same time the professional applies an equal resistance to the end of the client’s limb. 

For example, the professional applies resistance to the foot when performing a hamstring stretch, and this resistance is applied at the end of the range of motion (the point where the leg is at or near the vertical position when the client is lying on his or her back).

Remember, the teamwork component requires that the client must apply a maximum contraction at the same time. This method results in an isometric contraction and is held for a period of approximately six seconds. This is followed by the client’s conscious relaxation of the involved muscle and the implementation of a maximum passive stretch by the professional.

This procedure is repeated a few times, and it is believed that this technique accomplishes a superior stretch.

Neurophysiological Effects of Stretching

Myotatic Reflex

The stretch reflex is produced by neurophysiological responses in the body. The two neural receptors (sense organs) associated with the myotatic reflex are:

Golgi Tendon Organ (GTO)

A sensory organ located in the tendons that, when stimulated by too much contractile force, will cause its related muscle or connective tissue to relax in order to protect against injury.

Muscle Spindles

Fibers in the muscle tissue that protect against too much stretch, such as in ballistic stretching (rapid bouncing).

When the muscle spindle is stimulated from ballistic stretching, it causes the involved muscle to contract as protection against this excessive stretch. Once this occurs, another rapid bounce or excessive stretch against the contracted muscle could cause serious damage to the muscle or its connective tissue.


The components of muscles, tendons, and joints where special nerve endings detect any changes in movement, position, physical tension, or forces that occur to the body during an activity. These reactions enable the moving body part to gain a sense of relativity to its surroundings.

Safety Responses to Muscle Contraction & Muscle Stretching

Reciprocal Innervation Inhibition

Remember, when a muscle is contracted (the agonist muscle), there is another muscle that is stretching and opposing that action (the antagonist muscle).

Reciprocal innervation inhibition refers to the body’s protective reflex reaction to safeguard against muscle contraction, inhibiting the action of the antagonist’s muscle. For example, when the quadriceps is contracted, the action of the hamstring is inhibited as a protective reaction.

Muscle spindles are the sensory organs responsible for this reflex reaction.

Autogenic Inhibition

Under normal conditions and up to a certain point, muscles will contract as a protective action against too much stretching. Autogenic inhibition refers to the body’s protective reflex action against a stretch that is extreme enough to cause a rupture.

This action causes the muscle to suddenly stop contracting and enables the muscles to relax.

The Golgi tendon organ is the sensory organ responsible for this protective reflex reaction.

Common Musculoskeletal Injuries and Conditions

Sprains versus Strains

These two terms are often used inaccurately. Specifically, some people use the word sprain when the correct term would be strain and vice versa. So it is important to learn the difference:

  • Sprain refers to a ligament or joint capsule that has been overstretched or torn.
  • Strain refers to a muscle or tendon that has been overstretched or torn.


Inflammation of a tendon results in pain and limited function to the affected area. It is extremely important to understand that tendonitis can possibly lead to a tendon rupture, so it is critical that you never ignore an inflamed tendon.

Also, people who have had cortisone injections to treat tendonitis have a greater chance of it leading to a tendon rupture. Medical attention is recommended.


Inflammation of the bursa, which results in pain in the affected area. The bursa is a fluid-filled sac that is covered by a synovial membrane. Inside the sac is a capillary layer of viscous fluid that acts as a cushion between the bones and tendons, or as a cushion for muscles around a joint, or both. 

The bursa reduces friction between the bones, which enhances free motion. Most frequently, bursitis occurs in the shoulders, elbows, hips, and knees. Medical attention is recommended.


When a bone is separated from its normal position in the joint, such as a shoulder dislocation.


A partial separation (dislocation) of a joint.


A high-risk position at a joint where the angle between the two involved bones is beyond the neutral position.

An example of hyperextension at the shoulder joint would be doing the pull-down exercise behind the head. A safer method would be doing the pull-down exercise in front of the head where there would be no hyperextension at the shoulder joint.


A sudden disturbance of electrical activity within the brain after a severe blow to the head, neck, or face, which may result in permanent damage to the brain.

The probability of seriousness increases for those who have had multiple concussions. A severe blow to another part of the body may also cause a concussion when the forces are powerful enough to be transmitted to the head.

Concussions may or may not result in unconsciousness. If a person does become unconscious, it usually lasts only a few seconds. Accidents and sports are leading causes of concussions.

Football players, boxers, and people who participate in violent sports are more likely to sustain concussions. Those who have suffered a concussion should seek immediate medical attention.

The usual symptoms immediately following a concussion include confusion, dizziness, headache, seeing stars, feeling dazed, slurred speech, blurred vision, difficulty remembering, and vomiting.

Low Back Pain

There are many possible causes for low back pain, including strains, sprains, ruptured disks, or disease. Consequently, we recommend that a physician diagnose all back pain.

Sometimes a program of core exercises (abdominal muscle strength exercises) can relieve back pain. The abdominal muscle group can assist in supporting the torso, thus relieving some of the strain placed on the lower back.

When an individual is in pain or spasm, the use of ice is a very effective way to relieve this condition. However, swift medical attention is recommended.

Tennis Elbow (Epicondylitis)

Inflammation and pain at the elbow joint is a result of overusing the forearm muscles. Epicondylitis typically occurs with people who play tennis or golf, lift weights, or participate in any other sport where excessive or improper use of the forearm can occur.

The recommended treatment is to give the affected area partial or total rest and to treat with ice. Medical attention is recommended for this condition.

Common sense and correct training practices should always be implemented for any sport in order to help prevent epicondylitis.

Biceps Tendon Rupture

The bicep muscle has two separate tendons (the long head and the short head), which are located near the shoulder joint. When there is a rupture it usually occurs to the long-head tendon.

One common cause is using too much weight during bodybuilding. Another common cause may be due to an accident where a powerful, external force is exerted on the bicep while it is in a contracted position. A biceps tendon rupture is a medical emergency and the individual should immediately be brought to a hospital emergency room.

Shoulder Impingement Syndrome

Also known as a pinching injury, shoulder impingement is caused when the rotator cuff muscles and the bursa cannot pass smoothly through the coracoacromial arch, a narrow bony space that is located at the top of the shoulder.

This restriction causes inflammation to the rotator cuff and bursa, which is then followed by pain and swelling. These painful conditions are referred to as rotator cuff tendinitis and bursitis, respectively, and cause pain when raising the arms above the head.

Shoulder impingement is especially limiting for those who are weight lifters, swimmers, tennis players, baseball players, painters, and others who do work were raising the arms over the head is required. Medical attention is recommended.

Rotator Cuff Tear

The rotator cuff is a group of four muscles located at the shoulder:

  • Supraspinatus: responsible for the abduction of the arm.
  • Infraspinatus: responsible for lateral rotation of the arm.
  • Teres minor: responsible for lateral rotation of the arm.
  • Subscapularis: responsible for the medial rotation of the arm.

Certain diseases and injuries may cause tears to one or more of these muscles, resulting in pain and limited function. Medical attention is recommended.

Common Leg Injuries and Conditions

Shin Splints

Any pain occurring to the front-inside area of the lower leg along the tibia, caused by inflammation to the attachment of the deep muscles in that area.

Because diagnosis is sometimes challenging, and shin splints are sometimes thought to be stress fractures or vice versa, it is important to understand two major differences:

  • Shin splints affect muscles, the pain is not necessarily localized, and it can affect either a small area along the tibia or run the entire length of the tibia.
  • Stress fractures affect bones, and the pain is localized.

Shin splints are a muscle overuse injury that usually results from the repetitive pounding effects of running, including intrinsic and/or extrinsic factors. When this activity is reduced or stopped, the pain will usually decrease.

It is helpful to apply the methods outlined in the RICE procedure, and treatment usually includes strengthening and flexibility exercises for the leg.

If the pain continues, there is a possibility that the condition may instead be a stress fracture. Medical attention is recommended to diagnose and treat the problem.

Ankle Sprains

The most common site of ankle sprains is to the outside of the ankle, although on rare occasions, it does happen to the inside of the ankle.

The usual symptoms are swelling and an inability to walk on the affected foot. Within a couple of days, discolouration of the ankle usually appears.

It is important to apply the methods outlined in the RICE procedure immediately after the injury to prevent additional swelling and further injury. Medical attention is recommended.

Plantar Fasciitis

Inflammation of the plantar fascia, which is the primary supportive soft tissue that comprises the sole of the foot. Plantar fasciitis results from recurring trauma that causes chronic inflammation to the plantar fascia.

Common causes are running, improper training technique, always running in the same horizontal direction along a hill, and improperly fitting or worn-out footwear. It is also believed that high arches can make a person more likely to suffer from this condition.

The best treatment is to eliminate the cause. Medical attention is recommended.

Achilles Tendonitis and Rupture

The Achilles tendon is a powerful tendon that attaches both the gastrocnemius and the soleus muscles to the heel.

There are a great variety of causes of inflammation or rupture, including sports involving jumping (e.g., basketball, volleyball, or aerobics) or footwear that is poorly cushioned or has stiff soles.

If possible, eliminate the cause of inflammation to enable the tendon to heal. It is extremely important to understand that tendonitis can possibly lead to a tendon rupture. Therefore, it is critical that you never ignore an inflamed tendon.

Also, people who have had cortisone injections to treat the inflammation have a greater predisposition to a tendon rupture. A ruptured Achilles tendon is a medical emergency and the individual should immediately be brought to a hospital emergency room. 

Chondromalacia Patella

Pain on the back of the patella (kneecap) due to the softening of cartilage there. The word chondromalacia specifically means “soft cartilage.” In this condition, the articular cartilage gets soft and becomes diseased.

For the purpose of making a diagnosis, it should be noted that pain around the kneecap does not necessarily indicate the condition known as chondromalacia patella. Medical attention is recommended.

Patellofemoral Pain Syndrome

Pain around and under the patella (kneecap) due to a tracking problem.  This painful condition is sometimes mistaken for chondromalacia patella.

Tracking problems of the knee are often caused by a structural abnormality or some imbalance in the lower limb. In this situation, the patella does not have normal movement along the body groove that lies below the patella. The abnormal tracking is usually to the lateral side (outside).

In addition to pain, symptoms include swelling and grinding. If swelling is present, it will be around and above the knee. To treat the pain and swelling, it is helpful to apply the methods outlined in the RICE procedure.

Common causes of this problem are squats or leg extensions with too much weight, improper form, and other exercises, including running, where intensity or duration is too excessive. Strengthening and flexibility exercises for the leg are excellent preventative measures.

Other people may suffer from biomechanical problems such as muscle imbalances, which require professional help. Medical attention is recommended.

Patellar Tendonitis (Jumper’s Knee)

Inflammation of the patellar tendon, which extends from the bottom of the patella downward for approximately one to two inches. Inflammation of this tendon is usually caused by repetitive jumping activities, such as basketball, high jumping, volleyball, and certain aerobics.

When the condition first develops, the pain is usually present only after the activity. If the condition worsens, the pain becomes more constant. The best overall treatment is cutting back or eliminating the particular type of activity that causes the problem. Strengthening and flexibility exercises for the leg are excellent preventative measures.

It is extremely important to understand that tendonitis can possibly lead to a tendon rupture. Therefore, it is critical that you never ignore an inflamed tendon. Also, people who have had cortisone injections to treat the inflammation have a greater predisposition to a tendon rupture. Medical attention is recommended.

Iliotibial Band Syndrome (ITB)

The iliotibial band is a thick structure of fascia that extends down across the lateral (outside) section of the knee. The most common cause of inflammation to the iliotibial band is frequent running on uneven ground, downhill running, or running along a sloped surface.

The pain associated with this condition is usually felt just above the knee, and in more severe cases, the pain is felt up along the lateral thigh area.

The best treatment is cutting back or eliminating the particular type of running that causes the inflammation. Medical attention is recommended.

Cartilage (Meniscus) Tears

The medial and lateral cartilages (meniscus) are vital for the stability and cushioning of the knee joint. There are many reasons why cartilage can become torn, including injury, disease, and athletic activities such as weight lifting (particularly squatting), aerobic exercises, or running. 

In fact, any activity that subjects the knee to either prolonged stress or to excessive weight can cause a cartilage tear. Forces that cause the knee to bend or straighten too far also can result in a tear.

The usual symptoms are pain, swelling, clicking, popping, locking, giving way, and crackling (crepitus). Meniscal tears usually require arthroscopic surgery. Continuing to exercise with a tear is not advisable. Medical attention is recommended.

Anterior Cruciate Ligament (ACL) Tears

The ACL is located in the centre of the knee and is vital for the stability of the joint. ACL tears usually occur in sports such as football and basketball as a result of a blow to the outside of the knee. They can also occur as a result of not landing properly after a jump or getting shoes caught in an irregularity of the playing surface.

Diseases such as osteoarthritis can predispose the knee to an ACL tear. Symptoms include swelling, pain, popping, and instability at the knee joint.

If the ACL sufferer wishes to continue exercising or participating in a sport, surgery is the likely course of action. Medical attention is recommended.

Overstretching (Stretch Weakness)

Stretch Weakness

A condition that results when muscles have been overstretched for an extended period of time. The weakening effect on muscles creates a vulnerability to injury. It is important to use proper stretching techniques and to understand that “more does not mean better.”

Techniques Used to Treat Muscle Injury (RICE)

Many muscular injuries can benefit by the immediate use of RICE techniques, but always consult a physician before using these techniques.

The acronym “RICE” stands for:

  • Rest
  • Ice
  • Compression
  • Elevation


Avoid activities that affect the injured area. Rest is required in order to allow damaged tissue an opportunity to heal.


Often the first treatment following an injury, ice should be applied for a period of twenty to thirty minutes at a time, or as medically recommended. Be sure to use a layer of insulation, such as a towel, to prevent damage to the skin.

Depending on the severity of the injury, the application of ice should be continued between four to eight times per day, or as medically recommended.

The benefits of using ice on an injury include reducing inflammation and swelling, which promotes more rapid healing.

Caution: Do not apply ice to a numb area.


The use of an elastic bandage is a highly effective way to compress an injured area in order to prevent or reduce swelling by forcing fluids back into the body, which in turn promotes more rapid healing.


Once the first three measures have been taken, raising the injured part of the body slightly above the heart enables gravity to assist in the reduction of swelling as well.

Muscular System Testing Devices

Electromyogram (EMG)

When muscles are active, they produce an electrical current. This current is usually proportional to the level of muscle activity.

EMGs are used to detect abnormal electrical activity of muscles due to health conditions or injury. Examples include damage to nerves in the arms and legs (peripheral nerve damage), inflammation of muscles, disk herniation, muscular dystrophy, myasthenia gravis, amyotrophic lateral sclerosis (ALS), and others.


Tests for muscle forces during exercise (i.e., the force exerted by a muscle). A typical example would be to measure the force exerted by the quadriceps muscle during a leg extension exercise.


An angle gauge is used for testing a person’s range of motion (the distance and direction a joint can move between the flexed position and the extended position). Medical assessments pertaining to health conditions, post-operative limitations, and injury are the primary reasons for performing this test.


Another type of angle gauge is used for testing a person’s range of motion.

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