Muscle Facts

Muscles ['mə-səls]

A body tissue producing movement; part of the body's muscular system.

Diagram of human arm, muscle, and skeleton

Wiggle your toes. Now smile. Wave your hand. Pat your stomach while rubbing your head. Were you able to do these things? Thank your muscles. We have over 600 muscles in our bodies. Many of our muscles allow us to move. And they couldn't help us move without the assistance of our skeletal system. But not all of our muscles are responsible for movement. Some of our muscles have other jobs. Let's take a look at the types of muscles we have.

Types of Muscles

Happy children perform physical exercises in gym with a coach

Our bodies have three kinds of muscles. The smooth muscles, the cardiac muscles, and the voluntary muscles.

Diagram of the 3 types of muscles

Each of these three muscle types have a specific job to do and each of them look entirely different under microscopes.

The smooth muscles are the ones that are responsible for parts of the body like the digestive system, the blood vessels, and the kidneys. You have no conscious control of the smooth muscles or the jobs that they do. Our nervous system controls the smooth muscles.

We don't control the cardiac muscles either. These are the muscles of the heart. They keep our hearts beating every single day of our lives. They squeeze blood through our bodies continuously in a rhythm called our heartbeat.

The voluntary muscles are attached to our bones and allow us to run, hop, swim, kick, dance, write, and smile. And that's just the beginning. We have control over most of these muscles. That's why they are called voluntary. These are often referred to as the skeletal muscles and they attach to the bones of the skeleton at each end of the muscle by tendons.

3D rendering of the human skeleton with muscles attached

The voluntary muscles work very closely with the skeletal system. Together they make up the musculoskeletal system. Many scientists and doctors do not separate the two into distinctly different systems but think of them as one.

How Muscles Work

Muscles have two basic movements. They can tighten up (contract) or they can relax. So they always work in pairs. When you move your arm up to your mouth to get a drink of water, some muscles contract to move your hand closer to your face. Others are relaxing. When you are ready to put the glass back on the table, a different set of muscles contract so that your arm moves away from your face. The first set then needs to relax so that the contracting muscles can do their job. It sort of works like two people holding a rope. Imagine one person pulling on the rope to get the rope closer to themselves. The other person needs to relax in order for the rope to move. Then when the rope is moved toward the second person, the first person must relax.

Diagram of muscle movement through contraction and relaxation

Muscles Have Names

Fascicle muscle shapes
Image courtesy of OpenStax College

The voluntary muscles of your body have a huge job.

They must be available all of the time to get you moving at the smallest of a need. Like when that mosquito lands on your arm and you slap it. Or you jump up to answer the phone. Many times we don't plan in advance to do the moving we do. But our muscles are ready anyway.

Some of the muscles in our body can be very long — like the sartorius muscle which runs from the hip all the way down to the knee. Or very short — like the stapedius muscle which is in the middle ear and contributes to our ability to hear.

Our muscles are grouped by names for the jobs that they need to perform. The deltoids are located in the shoulders. They allow you to throw a ball or swim or do pull-ups on the monkey bars. They move your arms back and forth and around.

Young athlete lifting barbell in gym

Your pecs or pectorals are the large muscles in your chest. These help you lift things. Many bodybuilders work out these muscles so that they become very large. Boys tend to get larger pecs than girls.

Kids doing abs exercise with fitness balls

In your abdomen area are the abs, as they are often called. These are the ones that you tighten when you do sit-ups.

Your arms and legs have some very strong muscles. The bicep are the ones you flex when you do that "muscle showing thing" with your arm. Your quadriceps are the thick muscle on the front part of your thigh. When you run that muscle gets to going.

And let's not forget the gluteus maximus. That is the big muscle that you sit on. And so much fun to say!!

Muscles Have Needs

Girl eating meal, outdoors

Good, healthy muscles help us to move, help our heart to beat and our other organs to function properly. So how do we make sure that the muscles are healthy?

First of all, your muscles need good healthy food choices. The food you eat feeds your muscles. You might not think of it that way, but truly that is why we eat. Not just to taste good or to fill your stomach. So eat a balanced diet of fruits and vegetables with some good protein choices. To learn more about healthy eating, visit the Science Trek Nutrition site.

girl drinking water after workout

Muscles are always in need of water. Let's face it, our bodies are mostly water. So be sure to drink lots of water during the day. More if you are doing lots of physical exercise or it is hot.

You also need to keep those muscles in good shape by exercising them regularly. Run, play games, play in a sport, walk, climb, throw a ball, jump, swim, and make sure to move those muscles often. This includes your heart muscle which also needs exercise. When you do an activity that makes your heart beat faster, you are giving it the needed workout too.

Muscles use a lot of energy and oxygen. That is why we feel tired after a huge workout. We also breathe heavily to replace the necessary oxygen that the muscles use. Run a lap or two around the school grounds. You will be breathing faster and be more tired than you were when you started.

Group of kids exercising in the boot camp

When you work out, you need to make sure to do it correctly. Do a warm-up and a cool-down when you take on a physical activity. This allows your muscles to break into it gently and to relax gently. This prevents injury to muscles. Don't keep working on a muscle if you have pain. Pain can be part of exercise, but it might be due to injury. So be cautious and seek help from an adult if you need to.

Be extra cautious when lifting. A person can do serious injury to themselves when lifting heavy objects such as furniture or boxes. Always use the knees to get that object off the floor, not the back!! For more information about lifting, check out this slide show from the Mayo Clinic.

Wear protective gear! Be sure to put on a helmet before riding a bike or playing a sport where a helmet is part of the game gear. Don't forget the knee and shin pads. Always make sure to cover the parts of your body that might take the most physical abuse from your sport or activity. This helps to keep the bones and muscles safe and lets you play again.

Muscle Injury

Injuries can sometimes happen when we play hard. But knowing how and why can be helpful.

During exercise, our muscles can be susceptible to tiny tears. These tears heal up in a very short time, but they can make us feel some pain in the meantime. A little ice on the painful spot and staying off of it for a while will usually do the trick.

Child getting walking boot placed on sprained ankle by nurse in exam room

But sometimes, a more severe form of this injury, known as a sprain can occur. Most of us have sprained an ankle at one time or another. This likely happened by twisting the ankle or can even happen to a knee or a wrist. A trip to the doctor might be in order just to make sure that no bones are broken.

The doctor will probably take an x-ray to see into the painful spot. They can see what damage has occurred and know what form of treatment must take place. An X-ray is not painful, but you might have to move your painful body part for the X-ray technician and that might hurt some.

Muscles Fun Facts

  • There are 40-plus muscles in the face
  • Not everyone has the same number of muscles
  • There is some confusion about how many muscles are needed to smile and frown
  • The biggest muscle is the gluteus maximus
  • The hardest working muscle is the heart
  • The masseter muscle in the jaw can have a force as great as 200 pounds when a person bites down
  • Goose bumps happen when tiny muscles at the bottom of the hair follicle contract
  • Rapid muscle contractions when the body gets cold is called shivering
  • The tongue is a muscle and has its own "fingerprint" or "tongueprint"

Muscles Quiz

Now that you know everything there is to know about muscles, take this quiz and see if you can answer all of the questions. The quiz is online and part of the National Institute of Arthritis and Musculoskeletal and Skin Diseases — find the red box and click on it.

Funny strong child

Top 10 Questions

December 2013

Thanks to Dr. Anthony Joseph, physician, Family Practice and Sports Medicine for the answers.

  1. What are muscles made of?

    Muscles are made out of a substance called protein. Protein gives the muscle its structure and holds it together. (From Deborah at Cynthia Mann Elementary School in Boise)

  2. Can you transplant a muscle?

    One of the muscles we can transplant is the heart muscle. It's done almost every day around the world, and there are various programs to save the heart. The heart is one big muscle, and it can be transplanted from one person and put into another person. (From Brody at Valley View Elementary School in Boise)

  3. How many muscles do we have in our body?

    We have approximately 650 muscles in our body. (From Amy at Cynthia Mann Elementary School in Boise)

  4. Why do muscles hurt after exercise?

    There are two reasons why our muscles hurt after we exercise. First, immediately after exercise our muscles will accumulate a substance called lactic acid. The lactic acid in your muscles will cause them to burn and ache. And second, there is a delayed response. You may notice your muscles aching one or two days after you run or lift hard. The cellular structure of the muscle actually breaks down and tears. This gives your body stimuli to make a stronger muscle. So, it comes back being stronger than it was. (From Kendrick at Kamiah Elementary School in Kamiah)

  5. How come we shiver or get goose bumps when we are cold or scared?

    We have a series of involuntary muscles in our skin. These are muscles that we don't tell to contract. When these muscles contract, they pinch our skin in a method that creates little bumps. We call these goose bumps. These little bumps tell our skin to take the blood that normally goes to it and divert it back into our body. This helps us keep that warm blood inside ourselves. We also shiver as a way to contract our muscles. Again, we don't tell our muscles to do that. Usually, after we get goose bumps, we start shivering. The shivering is our muscles generating energy. This energy, which is stored in our muscles, helps create heat for our bodies. (From Reese at Dalton Elementary School in Dalton Gardens)

  6. What is the most important muscle in your body?

    It's a matter of opinion, but I would say that the heart is our most important muscle. If it stops functioning, then we stop functioning. (From Cabree at Caldwell Adventist Elementary School in Caldwell)

  7. Why is exercising important for a healthy muscle?

    Exercise does several things: It not only strengthens the muscles of your whole body and holds your skeleton together, but it also strengthens your heart. Your heart requires exercise to make it stronger so that if something happens to you, it can respond more forcefully. Extra force in the muscles of our body and in our heart keeps us going throughout our lifetime. (From Tony at Caldwell Adventist Elementary School in Caldwell)

  8. Are all muscles made of the same thing?

    We have different muscles in our bodies. The voluntary muscles are made of the same proteins and the same structural makeup. The same holds true for our involuntary muscles, either in the smooth or the cardiac muscles. They are a little bit different in their structure, but all of those categories of muscles have the same substance. (From Kyle at Dalton Elementary School in Dalton Gardens)

  9. What is the thickest muscle?

    The thickest muscle in the body is the gluteus maximus. That's the muscle that is behind you, known as your bottom. It's a muscle you sit on, but it is a very powerful muscle and is used for running, jumping, and other activities where you need to control your legs. (From Jennifer at Caldwell Adventist Elementary School in Caldwell)

  10. Do muscles have fluids in them?

    Muscles do have fluid in them. They have a very large blood supply. The majority of blood is fluid. Also, within the structure of muscle, we will find water. Water helps carry the calcium and other substances that help the muscles function and contract. (From Jaden at Cynthia Mann Elementary School in Boise)