Muscles: What To Know

Reviewed by Poonam Sachdev on September 01, 2022

What are muscles? How many muscles are in the human body?

There are over 600 muscles in the average human body. Muscles have many responsibilities. For example, some muscles help you to move, some help digest food, and others help to pump blood throughout your body. Muscles have many other jobs, too, depending on the muscle involved. 

Since muscles are a vital part of our body, keeping them strong is important. However well you maintain your muscles, though, there are still certain injuries and diseases that your muscles are susceptible to, which can hinder their performance. 

What Are Muscles?

Muscles are soft tissues that reside throughout the body. One well-known and critical muscle is the heart. This muscle is hard-working, beating thousands of times daily and allowing blood to flow through your body. Other muscles, such as the quads, glutes, hip flexors, and hamstrings, help you to run. Respiratory muscles such as the diaphragm, rib cage, and abdominal muscles help you to breathe. 

Maintaining a healthy lifestyle can help your muscles function properly. To keep your muscles strong, you should maintain a healthy weight, eat a well-balanced diet, and get sufficient exercise. Additionally, you should consult your doctor regarding any necessary screenings for muscle-specific diseases and conditions.  

Muscle Types

There are three primary types of muscles in the body: 

  • Skeletal: Skeletal muscles are the muscles that are attached to bones by tendons and help to move certain body parts such as the legs and arms. One example of a tendon connecting skeletal muscles is the Achilles tendon. It is the largest tendon in the human body and is located behind the ankle. Skeletal muscles coordinate with the nervous system, which sends voluntary signals to the muscles to tell them to contract or relax. Long cells called muscle fibers make up skeletal muscle tissue. They are organized into bundles. 
  • Smooth: Smooth muscles are the second muscle type and exist in the walls of the body. For example, these muscles reside in the airways, stomach, and blood vessels. These muscles are involuntary since they work automatically. Smooth muscles assist in moving food throughout the digestive tract, help empty liquid from the bladder, and control the width of blood vessels. In addition, smooth muscles around the arteries shrink and expand to regulate blood flow.
  • Cardiac: The third type of muscle, the cardiac muscle, exists around the heart’s walls. This muscle is not only part of the muscular system but also part of the circulatory system, helping to circulate blood throughout the body.

Major Muscles

There are many muscles in our bodies. Aside from the heart muscle, which is one of the most important, there are a few other significant muscles that should be noted. These muscles, which are skeletal and aid in movement, include the: 

  • Deltoid muscles: The deltoid muscles reside in your shoulders and help them move. Movements as simple as a shrug of the shoulders occur thanks to the deltoid muscles.
  • Pectoralis muscles: Also known as the pecs, these muscles are located on both sides of your upper chest. These muscles may grow larger once puberty occurs.
  • Abdominal muscles: Abdominal muscles, or abs, reside underneath the ribcage. They become more prominent when toned through exercise.
  • Bicep muscles: Bicep muscles are the muscles in your upper arms. Contracting your bicep muscle makes them more visible underneath your skin.
  • Quadricep muscles: Quadricep muscles are located in the front of your thighs. Runners, bikers, and athletes often develop strong quadricep muscles due to using them in their day-to-day lives.
  • Gluteus maximus muscles: The gluteus maximus muscles are located in your butt. When you sit down, you’ll be sitting on these muscles.

What Are Muscles Made Of?

Although there are different types of muscles, all muscles consist of the same basic components. These components include hundreds of elastic fibers that are bundled together and wrapped in a thin transparent membrane known as a perimysium. 

Individually, myofibrils, which are blocks of proteins, create muscle fibers. Myofibrils each contain a special protein called myoglobin and molecules that help provide oxygen and energy to muscles, allowing them to contract. 

What Is the Function of Muscles?

Each type of muscle has its own functions, jobs, and responsibilities.

For example, the skeletal muscles work alongside the brain and nerves to cause movement. These components are known as the neuromuscular system. 

Muscles are attached to bones, internal organs, and blood vessels, and their primary function is contractibility. Most of the movement that happens inside the body is the result of contractability. This includes the ability to walk and run and more subtle movements like facial expressions and respiration. Additionally, muscle contractions also aid in other vital functions, such as joint stability, posture, and heat production. In fact, almost 85% of the heat produced in your body is due to the contraction of your muscles. 

Other muscle functions include: 

  • Breathing
  • Speaking
  • Swallowing
  • Seeing
  • Hearing
  • Digesting food
  • Delivering a baby 

Muscle Conditions and Diseases

Muscles are susceptible to various diseases, disorders, and injuries that can affect their performance. These conditions and diseases include: 

  • Certain cancers, including sarcomas
  • Neuromuscular diseases, such as amyotrophic lateral sclerosis (ALS)
  • Autoimmune disorders, such as myasthenia gravis (MG)
  • Muscle diseases like polymyositis, which result in inflammation and muscle weakness 
  • Cardiovascular diseases and venous diseases, such as coronary artery disease
  • Chronic pain disorders, such as fibromyalgia 
  • Genetic disorders, such as muscular dystrophy, which results in permanent muscle weakness
  • Bacterial and viral infections, including Lyme disease and malaria 
  • Back strains, accidents, trauma, and other injuries that can result in muscle cramps, spasms, and, in rare cases, paralysis 

In addition, certain medications can result in muscle pain and weakness. These medications include chemotherapy medications, medications that treat high blood pressure, and medications that cause severe allergic reactions. 

Signs and Symptoms Of Muscle Conditions 

It’s important to understand that many signs and symptoms associated with muscle conditions can result from another disease or condition. Furthermore, just because your muscles hurt or feel weak does not mean that something is wrong. Most of the time, muscle pain and weakness will clear up independently with rest and hydration. 

However, a few symptoms affecting the muscles warrant a consultation with your doctor. These symptoms include: 

  • Trouble swallowing
  • Breathing difficulties 
  • Problems moving and balancing 
  • Muscle pain, cramps, or twitches that don’t go away
  • Tingling and/or numbness 
  • Problems with vision 

Muscle weakness or pain that appears suddenly with no known cause can be a symptom of a serious health condition. Consult your doctor immediately if you experience such symptoms. 

Show Sources


BetterHealth Channel: "Muscles.”

Cleveland Clinic: “Muscle.”

KidsHealth: "Your Muscles.”

National Cancer Institute: "Introduction to the Muscular System.”


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