Skeletal Muscle: What to Know

Medically Reviewed by Dany Paul Baby, MD on September 01, 2022
Written by Cheryl Whitten
5 min read

Skeletal muscle is the type of muscle that controls movement. Problems with these muscles can be minor, life-threatening, or ongoing problems that make it hard to perform basic daily activities. 

Skeletal muscle includes the tissue fibers attached to your skeleton or bones and is responsible for all your movements. These muscles are also found at the openings of tracts in your body, like your throat, anus, and urethra. They’re often called voluntary muscles because you control when and how they work.

Skeletal muscles are found around some of the openings of your body and all over other parts of your body between the bones. The muscle attaches at one end of the bone, stretches across a joint, and attaches to another bone. Tendons (fibrous connective tissues) help keep your muscles in place on your bones. 

There are 3 types of muscle: skeletal muscle, cardiac muscle, and smooth muscle. Each of these has a different structure and role. 

While skeletal muscle attaches to your bones and helps you move, cardiac muscle is the muscle fibers of your heart and responsible for its pumping action. Smooth muscle is the muscle of your digestive tract, urinary system, arteries, veins, lungs, and others. It helps move food through your intestines, get rid of waste, regulate blood pressure, and influence lots of other activities. 

While skeletal muscle movement is voluntary, cardiac and smooth muscles typically move involuntarily. These muscles receive signals from the autonomic nervous system. 

Skeletal muscle function is important for daily activities and your overall health. 

Movement. Skeletal muscles initiate and stop movement. When these muscles contract, they shorten and pull on your bone, making it move. Skeletal muscles at openings allow you to chew, swallow, urinate, or pass stool. 

Stabilize the body. You also use skeletal muscles to hold your body upright and maintain posture. With constant slight adjustments, these muscles keep your bones stable and help avoid skeletal damage. 

Skeletal muscles also help keep your joints stable. Without these muscles, your bones would quickly become dislocated or misaligned. 

Maintain body temperature. Skeletal muscles help manage your body temperature. As they contract, your muscles use energy, known as ATP, which generates heat. 

For example, imagine yourself shivering when you’re cold. This is because your body detects a lower-than-normal temperature and makes your muscles tense and relax to generate heat. The released heat brings your temperature back to normal. 

Protect organs. Your skeletal muscles act as a shield and protect your organs, especially those in your abdomen. They also help support the weight of your organs.  

Storage. Your muscles store glycogen and amino acids, which are the building blocks of protein. Your body can use these amino acids to build proteins as needed and will release glycogen for energy during activity or starvation. 

There are many components of skeletal muscle anatomy. However, skeletal muscle is primarily made of muscle fibers, which are bundles of lots of proteins called myofibrils. 

Each myofibril contains smaller protein structures called sarcomeres. These have light and dark areas and create patterns of red and white lines called striation. Skeletal muscles are often called striated muscles. The sarcomeres allow your muscle fibers to contract and slide across each other so that the muscle shortens. 

Skeletal muscles also have nerve fibers and blood vessels that bring in oxygen and nutrients and remove wastes. Each muscle has three layers of connective tissue that support the muscle, including:

  • Epimysium: the outer layer of dense, irregular connective tissue around the whole muscle
  • Perimysium: the middle layer of connective tissue around bundles of fibers
  • Endomysium: the inner layer of connective tissue around individual muscle fibers 

The most common sign of a muscle problem is weakness. Some symptoms and signs, like pain or twitching, are also common, though these can be normal side effects of exercise or activity. 

Intense exercise can cause lactic acid and other chemicals to build up faster than your body can get rid of them, which can lead to soreness. These symptoms are normal and will usually go away on their own within 3 to 5 days. 

Signs and symptoms of more serious muscle problems can include:

The term for diseases that affect your skeletal muscles is myopathy. There are lots of types of myopathy, including:

  • Infections
  • Toxic myopathy, a case where medications or toxins cause muscle problems
  • Hormone myopathy, a case where problems with your thyroid, adrenals, or parathyroid cause muscle problems
  • Muscle enzyme defects that cause muscle fiber breakdown or movement problems
  • Mitochondrial defects, cases where gene changes affect the energy centers of muscles and cause weakness
  • Autoimmune diseases, cases where your immune system attacks your muscles and causes inflammation
  • Injuries 

Some specific myopathic diseases include:

Myasthenia gravis. Your immune system makes antibodies that block muscular receptors of a neurotransmitter called acetylcholine, among other things. Your muscles get fewer signals, which causes weakness and fatigue.

Muscular dystrophies. There are many types of muscular dystrophies. These are inherited conditions that cause muscle loss and weakness. Some types are mild, but others are severe and cause disability. 

Sarcopenia. This condition is a normal part of aging and causes muscle loss over time with age. As you lose muscle, you also lose strength and mobility, which can raise your risk of falling and injuring yourself. 

Rhabdomyolysis. Often called rhabdo, this condition occurs when your damaged muscles break down and release proteins and electrolytes into your blood. This condition can cause permanent organ damage and even death. 

Healthy muscles are important for your overall health. To keep your muscles in good shape:

  • Get regular cardio and strength training exercise.
  • Eat a healthy diet with lots of protein, vegetables, and fruit.
  • Maintain a healthy weight.
  • Stretch before and after exercise.

If you experience ongoing or severe muscle pain, weakness, or movement problems, talk to your doctor.