Skeletal Muscle

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.

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.

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.

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.

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.

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.