What is the function of muscles?

Written by Jean Mari A. Rojas

Reviewed by Dr. Reuben J C. Los Baños, Ph.D.

The term muscles came from the Latin word mus, which means “little mouse.” The naming of the term is because of how flexing muscles look like scurrying mice beneath the skin.

There are three types of muscles:

1. Skeletal muscles.
2. Smooth muscles.
3. Cardiac muscles.

Some muscles line the heart (cardiac muscles) and other hollow organs (smooth muscles). Both of these muscles have involuntary movement. 

Muscles make up most of our body mass, with 600 forces making up the entire muscular system. The muscular system combines with other body systems to achieve many functions.

The primary functions of the muscular system are contractibility and movement.

The muscular system’s primary function is contractibility. With this unique function, muscles are now responsible for almost all body movement. An exception to this is cilia, flagellum on sperm cells, and activity of some white cells.  

A combination of skeletal muscles, joints, and bones produces visible motions. These actions include walking and running.

• It helps in creating a quick response to our environment.

• Skeletal muscles also generate more subtle movements. These movements include facial expressions, eye movements, eating, and breathing.

Smooth and cardiac muscles work together to ease movement in the blood vessels and heart.   

• They work together to maintain blood pressure and circulate blood to the parts of the body.

Other functions of the muscular system include:

1. Maintain posture and body position. It helps keep the body upright, erect, and in the correct position when standing or sitting.

2. Skeletal muscles also help in stabilizing joints. Muscle tendons stretch over joints and contribute to their stability.

3. Muscle activity generates heat as a byproduct. This byproduct is essential in maintaining average body temperature. Almost 85% of the heat generated is from muscle contraction. When it is cold, our muscular system will increase movement to increase heat production. This movement is shivering. Blood vessels, lined with smooth muscles, also contract to maintain body heat.

Other functions: Organ protection, vision, urination, digestion, and respiration.

How are muscles made in the body?

Myogenesis is the production of muscle tissue from stem cells. It gets produced in the mesoderm during embryonic development. Myoblasts fuse into multinucleated fibers termed myotubes to create muscle fibers. Suppose adequate fibroblast growth factor (FGF) is available during early embryonic development. The myoblasts multiply.

Muscle formation comes with three stages:

1. Myoblasts fuse into multinucleated fibers termed myotubes to create muscle fibers.

In early embryonic development, these myoblasts proliferate. But only if enough fibroblast growth factor (FGF) is present. When the FGF runs out, the myoblasts stop division.

It also secretes fibronectin onto its extracellular matrix.

2. Myoblasts align into the myotubes.

3. Cell fusion itself.

Calcium ions are critical for development. Myocyte Enhance Factors (MEFs) that promote myogenesis. Serum Response Factor (SRF) plays a central role during myogenesis. It requires the SRF to express striated alpha-actin genes. The expression gets regulated by the androgen receptor.

It means its steroids can control myogenesis.

Muscular hypertrophy refers to the expansion and development of muscle cells. It refers to a muscle size expansion that occurs as a result of training. Toning or improving muscular definition by lifting weights during exercises increases hypertrophy.

There are three Mechanisms for developing muscular hypertrophy:

1. MECHANICAL TENSION

It uses heavy load and performs exercises through a full range of motion. It considers the time the muscle spends under tension provided by the external load (barbell, dumbbell, etc.). The more time spent with the haul, the more mechanical tension gets produced.

But, tension alone won’t result in maximal muscle growth. It has to go into a full range of motion.

2. MUSCULAR DAMAGE

DOMs (Delayed Onset of Muscle Soreness) result from micro-tearing of the muscle due to damage. It gets sustained during resistance training, coming from eccentric and concentric contractions.

The initiation of muscular injury stimulates mTOR pathways, which then trigger protein synthesis. It is here that the rebuilding of the damaged muscle begins.

3. METABOLIC STRESS

‘the burn’ or ‘the pump’ repetitions. It is getting into higher repetitions and taking short breaks intervals. It creates a continuous contracting and relaxing of the muscles. It results in a blood pooling effect that makes muscular (cell) swelling. It causes a restriction in blood supply to the muscle and a shortage of oxygenated blood. It results in less oxygen to feed the body during contractions.

It causes a massive build-up of metabolites such as lactate and hydrogen ions. The anabolic impact of the metabolic stress put on the muscles leads to molecular signaling. It also increases the body’s hormonal response.

Why is protein essential for muscle?

The human body consists of about 5 to 6 kilograms of muscle protein. Protein is the building block of our muscular system.

Your body requires protein to stay healthy. Its general function is to:

• Blood carries energy and oxygen throughout your body
• Help create antibodies that fight off infections and illnesses
• Help keep cells healthy and make new ones.

Strength training activity stimulates the process of muscle protein synthesis (MPS). But, it gets enabled when you eat protein. Eating the right amounts of protein will help maintain muscle mass and muscle growth.

The amino acid leucine is abundant in “fast-digesting” proteins. It aids in the stimulation of MPS. Slow digesting proteins, such as those found in eggs and milk may help in slowing down the MPS process.

Eating reasonable amounts of protein help increase muscular strength and mass. So in trying to gain muscles and be active, make sure always to have enough protein. Also, keeping the protein intake high will prevent muscle loss during the weight loss attempts.

Best sources of protein:

High-quality sources of protein include:

•  Fish, Poultry, Beef, or pork
• Tofu
• Eggs
• Dairy products

Plant-based sources include:

• Nuts
• Seeds
• Legumes, like beans, peas, or lentils
• Grains, like wheat, rice, or corn

What is the largest muscle of the body?

The gluteus maximus is the largest and heaviest muscle in the human body.  It is the gluteal muscles’ most superficial muscle. It makes it the enormous muscle at the hip, representing 16% of the total cross-sectional area. 

Gluteal muscles:

• Gluteus Maximus
• Gluteus Medius
• Gluteus Minimus

The origins of the gluteus maximus are:

• Posterior gluteal line of the ilium;
• The posterior surface of the lower part of the sacrum;
• Side of the coccyx;
• Aponeurosis of erector spinae;
• Sacrotuberous ligament;
• Gluteal aponeurosis;
• Attaches to thoracolumbar and its associated raphe

The insertions of the gluteus maximus are:

• The enormous proximal part inserts into the Iliotibial tract. It forms the majority of the fibers.
• The other fibers insert into the linea aspera of the femur.

• The aponeurosis joins to the femur’s gluteal tuberosity.

Because of its large size, Gluteus Maximus can exert a lot of force. As one of the muscles stretching the hip joint, it also helps maintain an erect posture. The Gluteus Maximus’ primary function is to extend and rotate the hip joint to the side. Upper fibers can abduct the hip while the lower fibers can adduct it.    

The Gluteus maximus and the hamstrings work in conjunction to produce different movements:

• Extending the trunk from a flexed position by pulling the pelvis backward;
• Bending forward;
• Superior fibers of the gluteus maximus extend the knee

Gluteus maximus has stability roles:

• Maintaining upright posture;
• Supporting of the lateral knee;
• Abducting of the medial longitudinal arch of the foot

Other functions include:

• self bracing mechanisms;
• supporting body weight while sitting;
• The quadriceps femoris can get weak or paralyzed. The gluteus maximus can get trained to produce functional knee extension.

A bruise to the gluteal region is the gluteal contusion. Some get anticoagulated or on blood thinners. Large amounts of bleeding can occur within and around the muscle. It can cause severe pain and swelling. Trauma causes the most gluteal injuries, either by fall or a direct hit to the area.

While a gluteal muscle strain occurs when a muscle or tendon gets stretched or in part torn. Overuse injuries are the leading cause of gluteal muscular strain. It can result in inflammation and damage to the muscular system.

The most common injuries experienced by athletes are gluteal tendinopathies. It stems from overtraining in squats and weightlifting. Inflammation of the hip and gluteus is a common running injury.

What is the smallest muscle in the body?

The stapedius muscle is the smallest in the human body, approximately 6 mm in length. Its location is in the middle ear’s tympanic cavity. It controls the vibration of the body’s smallest bone or known as the stirrup bone.

The origin of the stapedius: Pyramidal eminence of the tympanic cavity.

The insertion of the stapedius: Neck of stapes.

Although it is the tiniest skeletal muscle, the stapedius has a vital role in sound transmission and hearing. It’s the acoustic middle ear reflex’s effector component.

The sound threshold of a healthy person with normal hearing is around 85 dB. Vocalization-induced stapedius reflex reduces sound intensities. It reaches the inner ear by about 20 decibels.

The primary function of the stapedius is to protect the inner ear from loud noises. The facial nerve’s stapedial branch innervates the stapedius muscle. These autonomic fibers allow the muscle to take part in the auditory middle ear reflex. It protects the auditory system. 

Hyperacusis is a condition that causes normal sounds to get perceived as loud noises. This condition results from the paralysis of the stapedius. It allows wider oscillation of the stapes. It heightens the reaction of the auditory ossicles to sound vibrations, causing hyperacusis. 

Paralysis of the stapedius. It results when the nerve to the stapedius, a branch of the facial nerve, or its entirety, gets damaged. Example cases are Bell’s palsy, a unilateral paralysis of the facial nerve. Where the stapedius gets paralyzed, and hyperacusis may result.

Do muscles need oxygen?

Much like every other cell and organ of the body, the muscular system needs oxygen to function.

Oxygen gets carried via red blood cells, where it binds to a protein called hemoglobin. The heart pumps the red blood cells to the parts of the body. Afterward, the release of oxygen into the cells occurs. Oxygen then gets used for breaking down molecules.

Adenosine triphosphate (ATP) is fuel for the muscles. It is a molecule that is the primary energy source to keep our body functioning. Carbon Dioxide (CO2) and water (H2O) gets produced as a result.

Whether exercising or not, oxygen gets used to breaking down glucose. And glucose creates ATP. This process of breaking down glucose is aerobic metabolism, which requires oxygen.

Muscles need the energy to produce contractions. It gets derived from the ATP that is present.

When you exercise, your muscles consume more oxygen:

• Your heart rate and breathing rate rise, drawing more oxygen into the circulation. It results in the increased production of ATP;

• Increased heart rate and breathing to remove the amount of carbon dioxide generated 

Energy can also get produced by anaerobic metabolism, a process that does not need oxygen. When your body lacks oxygen or your other systems can’t get enough oxygen to your muscles, your body will go into anaerobic metabolism. The muscles will convert the glucose you have to into lactic acid. During an intense workout, this is when your performance begins to deteriorate. Deterioration and fatigue will make you feel weary.

Researchers from Sweden’s Karolinska Institute discovered about oxygen-sensitive enzyme FIH (Factor Inhibiting HIF). FIH’s role is crucial in transitioning from aerobic to anaerobic metabolism. According to the investigators, FIH will ensure that the muscles maintain aerobic metabolism for as long as possible. It will continue to be efficient in using oxygen before transitioning to anaerobic metabolism.

After exercising, your body will be in oxygen debt. It is necessary to refill debts and replenish the oxygen in your bloodstream. Cool-down exercises are essential for replenishing oxygen levels. Afterward, consume a protein-filled snack to replace your body’s glycogen storage.

Your body’s ATP levels get restored by combining oxygen and glycogen. It also aids the liver, kidneys, and muscles in the breakdown of lactic acid.

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