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.

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Muscle