What muscle has no bones?

Your Muscles

Did you know you have more than 600 muscles in your body? They do everything from pumping blood throughout your body to helping you lift your heavy backpack. You control some of your muscles, while others — like your heart — do their jobs without you thinking about them at all.

Muscles are all made of the same material, a type of elastic tissue (sort of like the material in a rubber band). Thousands, or even tens of thousands, of small fibers make up each muscle.

What Are the Three Types of Muscles?

You have three different types of muscles in your body:

• smooth muscle
• cardiac (say: KAR-dee-ak) muscle, and
• skeletal (say: SKEL-uh-tul) muscle

What Are Smooth Muscles?

Smooth muscles — sometimes also called involuntary muscles — are usually in sheets, or layers, with one layer of muscle behind the other. You can’t control this type of muscle. Your brain and body tell these muscles what to do without you even thinking about it. You can’t use your smooth muscles to make a muscle in your arm or jump into the air.

But smooth muscles are at work all over your body. In your stomach and digestive system, they contract (tighten up) and relax to allow food to make its journey through the body. Your smooth muscles come in handy if you’re sick and you need to throw up. The muscles push the food back out of the stomach so it comes up through the esophagus (say: ih-SAH-fuh-gus) and out of the mouth.

Smooth muscles are also found in your bladder. When they’re relaxed, they allow you to hold in urine (pee) until you can get to the bathroom. Then they contract so that you can push the urine out. These muscles are also in a woman’s uterus, which is where a baby develops. There they help to push the baby out of the mother’s body when it’s time to be born.

You’ll find smooth muscles at work behind the scenes in your eyes, too. These muscles keep the eyes focused.

What’s the Cardiac (Heart) Muscle?

The muscle that makes up the heart is called cardiac muscle. It is also known as the myocardium (say: my-uh-KAR-dee-um). The thick muscles of the heart contract to pump blood out and then relax to let blood back in after it has circulated through the body.

Just like smooth muscle, cardiac muscle works all by itself with no help from you. A special group of cells within the heart are known as the pacemaker of the heart because it controls the heartbeat.

What Are the Skeletal (Striated) Muscles?

Now, let’s talk about the kind of muscle you think of when we say «muscle» — the ones that show how strong you are and let you boot a soccer ball into the goal. These are your skeletal muscles — sometimes called striated (say: STRY-ay-tud) muscle because the light and dark parts of the muscle fibers make them look striped (striated is a fancy word meaning striped).

Skeletal muscles are voluntary muscles, which means you can control what they do. Your leg won’t bend to kick the soccer ball unless you want it to. These muscles help to make up the musculoskeletal (say: mus-kyuh-low-SKEL-uh-tul) system — the combination of your muscles and your skeleton, or bones.

Together, the skeletal muscles work with your bones to give your body power and strength. In most cases, a skeletal muscle is attached to one end of a bone. It stretches all the way across a joint (the place where two bones meet) and then attaches again to another bone.

What Are Tendons?

Skeletal muscles are held to the bones with the help of tendons (say: TEN-dunz). Tendons are cords made of tough tissue, and they work as special connector pieces between bone and muscle. The tendons are attached so well that when you contract one of your muscles, the tendon and bone move along with it.

What Do Face Muscles Do?

You may not think of it as a muscular body part, but your face has plenty of muscles. You can check them out next time you look in the mirror. Facial muscles don’t all attach directly to bone like they do in the rest of the body. Instead, many of them attach under the skin. This allows you to contract your facial muscles just a tiny bit and make dozens of different kinds of faces. Even the smallest movement can turn a smile into a frown. You can raise your eyebrow to look surprised or wiggle your nose.

And while you’re looking at your face, don’t pass over your tongue — a muscle that’s attached only at one end! Your tongue is actually made of a group of muscles that work together to allow you to talk and help you chew food. Stick out your tongue and wiggle it around to see those muscles at work.

What Are Some Major Skeletal Muscles?

Skeletal muscles come in many different sizes and shapes to allow them to do many types of jobs. Some of the biggest and most powerful muscles are your calf and thigh muscles. They give your body the power it needs to lift and push things. Muscles in your neck and the top part of your back aren’t as large, but they are capable of some pretty amazing things: Try rotating your head around, back and forth, and up and down to feel the power of the muscles in your neck. These muscles also hold your head high.

Because there are so many skeletal muscles in your body, we can’t list them all here. But here are a few of the major ones:

What’s the Deltoid Muscle?

• In each of your shoulders is a deltoid (say: DEL-toyd) muscle. Your deltoid muscles help you move your shoulders every which way — from swinging a softball bat to shrugging your shoulders when you’re not sure of an answer.

What Are the Pectoralis Muscles (Pecs)?

• The pectoralis (say: pek-tuh-RAH-lus) muscles are found on each side of your upper chest. These are usually called pectorals (say: PEK-tuh-rulz), or pecs, for short. When many boys hit puberty, their pectoral muscles become larger. Many athletes and bodybuilders have large pecs, too.

What Are the Rectus Abdominus Muscles (Abs)?

• Below these pectorals, down under your ribcage, are your rectus abdominus (say: REK-tus ab-DAHM-uh-nus) muscles, or abdominals (say: ab-DAHM-uh-nulz). They’re often called abs for short.

What Is the Biceps Muscle?

• When you make a muscle in your arm, you tense your biceps (say: BYE-seps) muscle. When you contract your biceps muscle, you can actually see it push up under your skin.

What Are the Quadriceps (Quads)?

• Your quadriceps (say: KWAD-ruh-seps), or quads, are the muscles on the front of your thighs. Many people who run, bike, or play sports develop large, strong quads.

What Is the Gluteus Maximus?

• And when it’s time for you to take a seat? You’ll be sitting on your gluteus maximus (say: GLOOT-ee-us MAK-suh-mus), the muscle that’s under the skin and fat in your behind!

Muscle

You have more than 600 muscles in your body. Some muscles help you move, lift or sit still. Others help you digest food, breathe or see. Your heart is a muscle that pumps blood through your body. Many injuries and diseases can affect how the muscles work. To keep your muscles strong, maintain a healthy weight, eat right and exercise regularly.

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Overview

What are muscles?

Muscles are soft tissues. Many stretchy fibers make up your muscles. You have more than 600 muscles in your body. Different types of muscles have different jobs. Some muscles help you run, jump or perform delicate tasks like threading a needle. Other muscles allow you to breathe or digest food. Your heart is a hard-working muscle that beats thousands of times a day.

Many disorders, injuries and diseases can affect how muscles work. These conditions can cause muscle pain, muscle spasms or muscle weakness. More severe disorders can lead to paralysis. Cardiomyopathy and other kinds of heart disease make it difficult for the heart to pump blood through the body.

Living a healthy lifestyle helps your muscles work like they should. You can keep your muscles strong by maintaining a healthy weight, eating a balanced diet and getting plenty of exercise. Be sure to see your provider regularly to screen for diseases and conditions that can lead to muscle problems.

What are the types of muscles?

You control some muscles voluntarily with the help of your nervous system (your body’s command center). You make them move by thinking about moving them.

Other muscles work involuntarily, which means you can’t control them. They do their job automatically. In order to work, they take cues from other body systems, such as your digestive system or cardiovascular system.

There are three types of muscle tissue in the body. They are:

• Skeletal: As part of the musculoskeletal system, these muscles work with your bones, tendons and ligaments. Tendons attach skeletal muscles to bones all over your body. Together, they support the weight of your body and help you move. You control these voluntary muscles. Some muscle fibers contract quickly and use short bursts of energy (fast-twitch muscles). Others move slowly, such as your back muscles that help with posture.
• Cardiac: These muscles line the heart walls. They help your heart pump blood that travels through your cardiovascular system. You don’t control cardiac muscles. Your heart tells them when to contract.
• Smooth: These muscles line the insides of organs such as the bladder, stomach and intestines. Smooth muscles play an important role in many body systems, including the female reproductive system, male reproductive system, urinary system and respiratory system. These types of muscles work without you having to think about them. They do essential jobs like move waste through your intestines and help your lungs expand when you breathe.

Function

What do muscles do?

Muscles play a role in nearly every system and function of the body. Different kinds of muscles help with:

• Breathing, speaking and swallowing.
• Digesting food and getting rid of waste.
• Moving, sitting still and standing up straight.
• Pumping blood through the heart and blood vessels.
• Pushing a baby through the birth canal as muscles in the uterus contract and relax.
• Seeing and hearing.

Anatomy

What do muscles look like?

All types of muscle tissue look similar. But there are slight differences in their appearance:

• Skeletal muscles: Many individual fibers make up skeletal muscles. Actin and myosin are proteins that make up the fibers. The bundles of fibers form a spindle shape (long and straight with tapered ends). A membrane surrounds each spindle. Providers describe skeletal muscles as striated (striped) because of the striped pattern the spindles create together.
• Cardiac muscles: These striated muscles look similar to skeletal muscles. Special cells called cardiomyocytes make up the fibers in cardiac muscles. Cardiomyocytes help your heart beat.
• Smooth muscles: The proteins actin and myosin also make up smooth muscle fibers. In skeletal muscles, these proteins come together to form a spindle shape. In smooth muscles, these proteins appear in sheets. The sheets give this muscle tissue a smooth appearance. You have all sizes of muscles in your body. The largest muscle is the gluteus maximus (the muscle that makes up your bottom). The smallest muscle is the stapedius, which is deep inside your ear. This tiny muscle helps you hear by controlling the vibration and movement of small bones in your ear.

Conditions and Disorders

What conditions and disorders affect the muscles?

A wide range of disorders, diseases, drugs and injuries can cause problems with how the muscles work. They include:

• Cancer and other disease: Multiple types of cancer (such as sarcoma) and other diseases can lead to muscle problems. These include neuromuscular diseases such as amyotrophic lateral sclerosis (ALS), autoimmune disorders such as myasthenia gravis (MG), and many types of myopathies (muscle disease). A disease called polymyositis causes inflammation in the muscles, leading to muscle weakness.
• Cardiovascular disease: Several kinds of venous disease and cardiovascular disease, including coronary artery disease, can cause problems with the heart and blood vessels. A heart attack can result when muscles in the blood vessels weaken.
• Chronic pain disorders:Fibromyalgia and other disorders cause chronic pain in the muscles all over the body.
• Genetic disorders:Muscular dystrophy is an inherited disorder (passed down through families). There are more than 30 types of muscular dystrophy. The disorder causes permanent muscle weakness.
• Infections: Bacterial and viral infections can damage muscle fibers. These infections include Lyme disease, malaria and Rocky Mountain spotted fever.
• Injuries: Many different injuries can cause muscles to tear or stretch too far (muscle strain). Back strains are a very common injury. Accidents, trauma and overuse injuries can cause muscle cramps or muscle spasms. In severe cases, these injuries can lead to paralysis.
• Medications: Certain drugs, such as chemotherapy medications, can cause muscle pain. Sore muscles can also result from medications that treat high blood pressure. Some people develop muscle weakness after having a severe allergic reaction to a medication or a toxic substance.

What happens to muscles during and after exercise?

Many people have sore muscles after working out. The soreness results from tiny tears (microtears) that happen when you put stress on a muscle. Usually, muscle soreness sets in a day or two after vigorous exercise. This is why providers call this condition delayed onset muscle soreness (DOMS).

As the muscles repair themselves and the tiny tears heal, the muscle tissue becomes inflamed. Within a few days, your muscles recover and the inflammation goes away. With continued exercise, the muscle tissue tears and rebuilds again and again. This process causes muscles to get bigger.

What are common signs or symptoms of conditions affecting the muscles?

Some of the most common signs of muscle problems include:

• Difficulty swallowing, shortness of breath or other breathing problems.
• Movement problems and balance issues.
• Muscle pain, cramps or twitching.
• Muscle weakness, loss of mobility or paralysis.
• Tingling or numbness.
• Vision problems (such as double vision) or droopy eyelids.

Many of these symptoms don’t necessarily mean something is wrong. Muscle pain or weakness often gets better with rest and hydration. If any of these symptoms come on suddenly, talk to your provider right away. Sudden muscle weakness or pain can be signs of a serious health condition.

What are some common tests to check muscle health?

Depending on your symptoms, your provider may recommend:

• Complete blood count (CBC), a series of blood tests that evaluate your overall health and check for infection.
• Electromyography (EMG) to measure how the nerves and muscles work.
• Imaging studies such as an MRI that show pictures of damage to muscles.
• Muscle biopsy to test a sample of muscle tissue for disease.

Care

How can I keep my muscles healthy?

To keep your muscles healthy, you should focus on staying healthy overall:

• Get plenty of exercise: Staying active can keep all of your muscles strong, including your heart. Try to do a combination of cardiovascular activity and weight-bearing exercises. Talk to your provider about an exercise program that’s right for you. To avoid injuries, be sure to warm up properly before exercise. You’re less likely to injure muscles that are warm.
• Eat right and make smart choices: Be sure to eat a balanced diet to keep your muscles strong. Avoid sodium and trans fats (such as in fried foods), which can lead to heart disease. If you smoke, talk to your provider about a plan to help you quit.
• Maintain a healthy weight: Carrying extra pounds can cause injuries. It also increases your risk of health problems, including high blood pressure. Talk to your provider about the most appropriate weight for your body and lifestyle. If you carry extra weight, ask your provider about a weight control plan.
• Rest when you need to: Give your muscles time to heal after a strain. You should also rest if you feel sore after rigorous exercise. Allowing your muscles time to repair and rebuild can help you avoid injury.
• Schedule regular screenings: See your provider regularly. Get screened for diseases that put you at a higher risk of muscle problems. Staying on top of your health allows your provider to detect problems early. That’s when treatments are more effective.

Frequently Asked Questions

When should I call my doctor about my muscles?

If you have muscle weakness or muscle pain that comes on suddenly, call your provider right away. Get emergency medical help if you have trouble breathing or swallowing, or if you have vision changes, chest pain or problems with balance. These could be signs of a serious health condition.

A note from Cleveland Clinic

Your muscles play an essential role in keeping you alive and helping you interact with the world. Some muscles help you see, hear and move. Others are responsible for helping you breathe or digest food. Everyone loses some muscle mass with age. To keep your muscles working properly, you should maintain a healthy weight, get plenty of exercise and eat a balanced diet. See your provider for regular screenings that can detect health problems that may lead to muscle problems.

Skeletal Muscle

Skeletal muscles comprise 30 to 40% of your total body mass. They’re the muscles that connect to your bones and allow you to perform a wide range of movements and functions. Skeletal muscles are voluntary, meaning you control how and when they work.

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Overview

What is skeletal muscle?

The majority of the muscles in your body are skeletal muscles. They make up between 30 to 40% of your total body mass. Tendons (tough bands of connective tissue) attach skeletal muscle tissue to bones throughout your body. Your shoulder muscles, hamstring muscles and abdominal muscles are all examples of skeletal muscles.

What’s the difference between skeletal, cardiac and smooth muscle?

There are three types of muscles in your body:

• Skeletal muscle: Skeletal muscles are voluntary muscles, meaning you control how and when they move and work. Nerves in your somatic nervous system send signals to make them function. If you reach for a book on a shelf, you’re using skeletal muscles in your neck, arm and shoulder.
• Cardiac muscle: Cardiac muscles are only in your heart. They help your heart pump blood throughout your body. They’re involuntary muscles that your autonomic nervous system controls. That means they work without you having to think about it.
• Smooth muscle: Smooth muscle makes up your organs, blood vessels, digestive tract, skin and other areas. Smooth muscles are involuntary, too. So, your autonomic nervous system controls them as well. For example, muscles in your urinary system help rid your body of waste and toxins.

Function

What is the purpose of the skeletal muscles?

The skeletal muscles are a vital part of your musculoskeletal system. They serve a variety of functions, including:

• Chewing and swallowing, which are the first parts of digestion.
• Expanding and contracting your chest cavity so you can inhale and exhale at will.
• Maintaining body posture.
• Moving the bones in different parts of your body.
• Protecting joints and holding them in place.

Anatomy

Where are the skeletal muscles located?

There are skeletal muscles throughout your body. They’re located between bones.

What are the skeletal muscles made of?

Skeletal muscles consist of flexible muscle fibers that range from less than half an inch to just over three inches in diameter. These fibers usually span the length of the muscle. The fibers contract (tighten), which allows the muscles to move bones so you can perform lots of different movements.

How are the skeletal muscles structured?

Each muscle can contain thousands of fibers. Different types of sheaths, or coverings, surround the fibers:

• Epimysium: The outermost layer of tissue surrounding the entire muscle.
• Perimysium: The middle layer surrounding bundles of muscle fibers.
• Endomysium: The innermost layer surrounding individual muscle fibers.

What do skeletal muscles look like?

Skeletal muscle fibers are red and white. They look striated, or striped, so they’re often called striated muscles. Cardiac muscles are also striated, but smooth muscles aren’t.

How heavy are skeletal muscles?

Although skeletal muscles typically make up roughly 35% of your body weight, this can vary from person to person. Men have about 36% more skeletal muscle mass than women. People who are tall or overweight also tend to have higher muscle mass. Muscle mass decreases with age in both men and women.

Conditions and Disorders

What conditions and disorders affect skeletal muscles?

A wide range of conditions can affect skeletal muscles, from mild injuries to serious or even life-threatening myopathies (diseases that affect skeletal muscles). A few are:

• Muscular dystrophies: This group of diseases causes progressive degeneration of skeletal muscle fibers. They’re the result of having an abnormal gene and can be inherited (passed down through families). There are many different muscular dystrophies.
• Myasthenia gravis (MG): This autoimmune disease prevents muscles and nerves from communicating as they should. It leads to severe muscle weakness and fatigue. MG can make it difficult to move, walk, speak, chew, see, hold your head up or keep your eyelids open. It can even lead to severe breathing problems.
• Rhabdomyolysis: This life-threatening condition causes a breakdown of muscle tissue. The damaged muscles release proteins, electrolytes and other substances into the blood. This can lead to serious organ damage. Traumatic injuries, heatstroke or severe overexertion can cause rhabdomyolysis.
• Sarcopenia: We gradually lose skeletal muscle mass as we age. Sarcopenia begins around age 40. By 80, we lose about 50% of our muscle mass. Sarcopenia can lead to loss of function, mobility, balance problems and falls. Obesity, hormonal changes and other health conditions can accelerate muscle loss.
• Strains: Muscle strains, or pulled muscles, occur when you overstretch muscle fibers. These injuries are usually the result of overuse. Severe strains can lead to partial or complete muscle tears.
• Tendonitis: Tendons connect skeletal muscles to bones. Tendon inflammation can make it painful to use these muscles. Like strains, tendonitis is usually caused by overworking tendons.

How common are skeletal muscle conditions?

Some skeletal muscle conditions, such as strains and age-related degeneration, are really common. Muscle injuries account for 10 to 55% of all sports injuries, and about 90% of those are strains. Others are fairly rare. For instance, myasthenia gravis affects between 14 and 40 people out of every 100,000 in the U.S.

Care

How can I keep my skeletal muscles healthy?

Take care of your skeletal muscles by:

• Doing regular strength conditioning and resistance exercises.
• Eating a nutritious, balanced diet.
• Maintaining a healthy body weight.
• Stretching and warming up your muscles before physical activity.

Frequently Asked Questions

When should I call my doctor?

Contact your doctor right away if you:

• Can’t move any part of your body.
• Experience numbness in your face or limbs.
• Have severe, sudden muscle pain or cramps.
• Have very dark urine or low urine output.
• Feel excessively weak or tired.

A note from Cleveland Clinic

Skeletal muscles are the most common muscles in your body. You use them to move your bones, so they play a vital role in everyday activities. Skeletal muscle injuries or diseases can have a profound effect on your life. It’s important to keep your muscles as strong and healthy as possible.

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Last reviewed by a Cleveland Clinic medical professional on 09/01/2021.

References

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• U.S. Centers for Disease Control and Prevention, The National Institute for Occupational Safety and Health. Rhabdomyolysis. (https://www.cdc.gov/niosh/topics/rhabdo/default.html) Accessed 9/28/2021.
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