Common Disorders of the Muscular System

Instructor: Amanda Robb

Amanda has taught high school Biology & Physics for 8 years. She received her M.Ed. from Simmon's College and M.S. from Tufts in Cellular and Molecular Physiology.

In this lesson we'll review the basics of the muscular system and explain three common disorders: strains and tears, rhabdomyolysis, and muscular dystrophy.

What Is the Muscular System?

When you think of muscles, you might picture athletes, or body builders in bikinis showing off six pack abs. You wouldn't be wrong, but muscles do so much more for the body. In fact, you are using your muscles all the time even in tasks as simple as talking, blinking, and eating. Muscles also comprise your internal organs, like your heart, stomach and diaphragm, which regulates breathing. All of the muscles in the body are collectively called the muscular system.

The human muscular system
muscular system

Some people have disorders of the muscular system, where part of their muscular system is damaged. The damage can be small, such as a sprained muscle, a common ailment most people have experienced, or it can be serious like the genetic disorder muscular dystrophy, where muscle breaks down over the person's life. Today, we'll look at three common muscle ailments: strains and tears; rhabdomyolysis, which was once rare but is being seen more and more in the fitness community; and muscular dystrophy.

Strains and Tears

Muscle strains occur when a muscle is over stretched and the muscle fibers tear. There are varying degrees of muscle strains, from a mild 'pulled muscle,' where there are tiny microtears but the muscle is still intact, to partial tears, which are macroscopic, to complete tears, where the entire muscle has ripped apart, which requires surgery. During a strain or tear, the muscles contract while also trying to extend, called eccentric contraction.

Hamstring strains commonly happen in athletes like sprinters, where the muscle is trying to contract due to a heavy load of the body, but also trying to extend to push the runner forward. The immediate symptoms will be a sharp pain and inability to run. Swelling may occur, as well as bruising and weakness.

Bruising like this hamstring is characteristic of a torn muscle
bruising due to a torn muscle

For pulls or partial tears, the solution is usually rest, ice, and elevation. You can take over-the-counter anti-inflammatory drugs to reduce inflammation as well. After the muscle is healed, some people need physical therapy to retrain the muscle and gain their strength back before returning to their sport.


Although once rare, rhabdomyolysis is making a comeback due to an increase in intense workouts like CrossFit. Rhabdomyolysis occurs when muscle cells explode, releasing excessive amounts of protein into your blood stream, causing kidney failure and death. In addition to over exertion, alcohol abuse, certain toxins, injuries that crush the muscles, such as a large object falling on you, and genetic conditions also can cause rhabdomyolysis. Medications, such as statins, are also known to cause rhabdomyolysis.

Mechanism of rhabdomyolysis

During extreme workouts participants push themselves to the limit. The intense, competitive nature of these workouts where participants work until utter failure, can lead to muscle trauma. Far more than normal muscle tears, which is how we build new muscle from lifting weighs, the muscle cells literally explode in rhabdomyolysis.

Extreme workouts can result in rhabdomyolysis
extreme workouts

Symptoms start with muscle weakness and soreness, which are common after a workout. However, these symptoms persist beyond normal levels as the muscles break down and release protein. The overload of protein in the blood causes urine to turn a dark brown, a sign you should be headed to the emergency room.

People get an IV with fluids and a solution called bicarbonate to help with the protein output. Some people may need dialysis, where a machine filters the blood for the kidney. Although some recover from this disorder, others might have permanent kidney damage, and the ability to build muscle will most likely no longer be the same.

Some patients with rhabdomyolysis will need dialysis to filter blood while their kidneys are damaged

Muscular Dystrophy

Muscular dystrophy is a genetic disorder where a protein involved in muscle growth, called dystrophin is not made. As a consequence, muscle breaks down over time and cannot be repaired. There are many types of muscular dystrophy, arising from over 50 mutations, or changes in our genetic code, that alter dystrophin.

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