You have more than 600 muscles in your body that you use almost constantly. Some move your body — others help your internal organs keep you alive. It’s OK to feel the occasional ache or muscle pain, but don’t ignore chronic (long-term) soreness or weakness.


What are muscles?

Muscles are pieces of soft tissue throughout your body. They help you do everything from holding your body still to running a marathon. Muscles also move and support your organs. Your heart is a hard-working muscle that beats thousands of times a day to keep you alive.

Because you have so many muscles, injuries and health conditions that affect them are common. Everyone has a sore muscle every once in a while, but long-term muscle pain, weakness and other symptoms can be signs of serious issues. Visit a healthcare provider if you experience muscle pain for more than a week, or if you’re having trouble moving. Go to the emergency room if it’s hard to breathe or swallow.


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What are muscles’ function?

Muscles move your body. They perform two types of movements:

  • Voluntary movements: Voluntary movements are actions you control. You choose to perform an action and your muscles move your body to make it happen. You use your nervous system to control these movements. Flicking your thumb to scroll through this article on your phone and sprinting around a track are both voluntary movements.
  • Involuntary movements: Involuntary movements happen automatically without you thinking about them. The muscles in and around your organs move involuntarily to keep your body working properly. Your heart beating and muscles in your chest and back moving your ribs when you breathe are examples of involuntary movements.

Your muscles use a combination of voluntary and involuntary movements to work with nearly all your body’s systems and functions. Different kinds of muscles help with:

  • Vision.
  • Hearing.
  • Breathing, speaking and swallowing.
  • Digesting food and getting rid of waste (peeing and pooping).
  • Moving, sitting still and standing up straight.
  • Pumping blood through your heart and blood vessels.
  • Giving birth.

Muscles also store and release energy your body uses as part of your metabolism.


What is the anatomy of muscles?

Your muscles are made of thousands of small fibers woven together. These fibers stretching and pressing together is what moves your organs or body. Your muscles weave together like a quilt that covers your body. They run in all directions and work together to move you.

What are the types of muscles?

Healthcare providers organize muscles by tissue type. There are three types of muscle tissue in your body:

  • Skeletal.
  • Cardiac.
  • Smooth.
Skeletal muscles

Skeletal muscles are part of your musculoskeletal system. They work with your bones, tendons and ligaments to support your weight and move you. Tendons attach skeletal muscles to bones all over your body.

Skeletal muscles are voluntary — they move when you think about moving that part of your body. Some muscle fibers contract quickly and use short bursts of energy (fast-twitch muscles). Others move slowly, like your back muscles that help with posture.

Cardiac muscle

Cardiac muscle (myocardium) makes up the middle layers of your heart. It doesn’t exist anywhere else in your body. Cardiac muscle squeezes and relaxes to pump blood through your cardiovascular system.

Your heart is an involuntary muscle — it beats on its own without your input.

Smooth muscles

Smooth muscles are involuntary muscles that line the inside of some organs. They do essential jobs like moving waste through your intestines and helping your lungs expand when you breathe.

Smooth muscles play an important role in many body systems, including the:


How many muscles are in the human body?

There are more than 600 muscles located almost everywhere throughout your body.

Your first thought when picturing muscles might be the biceps in your upper arms or the quads in your thighs, but muscles support almost every part of your body, many of which you’ll never notice.

Conditions and Disorders

What are common injuries or health conditions that affect muscles?

Muscle strains (pulled muscles) are the most common muscle injury. They happen when you overuse a muscle. The strands of muscle fiber are stretched beyond their limit and tear apart. You’ve seen this happen if you’ve ever tried to use an old bungee cord to hold something in place.

Many health conditions can affect your muscles, too, including:

Muscle symptoms

The most common symptoms of a muscle injury or health condition include:

Muscle tests

A healthcare provider may use a few different kinds of tests to diagnose muscle conditions or injuries:


How do healthcare providers treat muscle issues?

Which treatments you’ll need depends on the health condition or injury you have. Some conditions that affect your muscles are short-term issues. Others are chronic conditions and you’ll need to manage your symptoms for a long time.

You can manage many muscle injuries at home with the RICE method:

  • Rest: Avoid the activity that caused the injury. Try not to use the injured part of your body while it heals.
  • Ice: Apply a cold compress to your injury 15 minutes at a time, a few times a day. Wrap ice packs in a towel or thin cloth so they’re not directly touching your skin.
  • Compression: Wrap an elastic bandage around your injured muscle to help reduce swelling. Your provider can show you how to apply a compression wrap safely.
  • Elevation: Keep your injured muscle above the level of your heart as often as you can.


How can I take care of my muscles?

Stretching and warming up before exercise or physical activity are the best ways to prevent muscle injuries. Increasing your overall flexibility will also protect your muscles from injuries. The more flexible you are, the more room your muscle fibers have to stretch before they begin to tear.

Increase your activity level gradually. Don’t suddenly ramp up your training intensity or start exercising way more often than you usually do.

When should I see a healthcare provider?

Visit a provider if you’re experiencing muscle pain that doesn’t get better in a week with rest and other at-home treatments. Go to the emergency room if you have any of the following symptoms:

Additional Common Questions

Is a muscle an organ or a tissue?

Muscles are tissue. Smooth muscle tissue lines some of your organs, but most organs are also made of other types of tissue, too. Providers sometimes refer to the muscular system as one anatomical group that includes all your muscles. They might also include muscles as parts of other systems throughout your body.

Your heart is the only organ that’s also a muscle. It’s made of a special type of muscle tissue called cardiac muscle. Your heart is the only place in your body that has cardiac tissue.

What are muscle groups?

Fitness trainers or physical therapists may talk about strengthening or working out specific muscle groups. These are usually loosely defined.

It’s common to group muscles together by their location (like your chest muscles, leg muscles or back muscles) or what kind of movement they perform (abductors, flexors or extensors, for example).

Healthcare providers usually only classify muscles based on the type of tissue they’re made of.

A note from Cleveland Clinic

You have more than 600 muscles, and you use them constantly whether you’re thinking about them or not. Some muscles you can see and feel (especially after a big workout). Others — like your heart and the muscles that line some organs — silently keep you alive. It’s normal to feel sore or achy sometimes, but visit a healthcare provider if you’re constantly feeling muscle pain. You shouldn’t feel sore or painful all the time. Muscle pain can often be a sign of a condition a provider needs to diagnose and treat.

Remember, you don’t have to look like a muscular professional athlete to be healthy. Talk to your provider about ways to support your muscle (and overall) health. They’ll suggest exercises, movements or physical activities that’ll keep you strong, safe and healthy.

Medically Reviewed

Last reviewed on 01/23/2024.

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