Muscle Strain: Symptoms, Causes, and Prevention

Muscle strains are caused by overstretching and tearing muscle fibers, usually due to excessive force from a sport or activity. In addition, a strain can be a result of cumulative trauma from repetitive use. However, with the proper precautions, there are ways to prevent straining your muscles.

Key takeaways:

When we exert our muscles while exercising, we damage them. Therefore, to discuss and understand the mechanisms of muscle strain, we must first understand what happens to muscles during exercise.


Muscle-building mechanism

When we use our muscles during exercise, we produce microfiber muscle tears called micro tears. During the recovery (rest) period, the microtears heal and repair, stronger than before. This is the process of building muscles, leading to increased muscle strength and resting muscle tone — what we visualize when the muscles are relaxed. As a result, muscles are better prepared to handle a load (stress) next time. The soreness you feel after exercise is related to repairing the microfibers.

When a muscle fiber is stretched or torn, it will not undergo the normal repair process mentioned above, resulting in a strain. This is due to a muscle fiber being stretched or torn, and not microtears.

Note that each skeletal muscle is made up of hundreds to thousands of muscle fibers.

Symptoms of a muscle strain

Symptoms of a muscle strain can include the following, but they vary depending on the type of strain:

  • Sudden onset of pain
  • An audible "pop" at the muscle
  • Swelling
  • Bruising (purple that eventually turns yellow)
  • Loss of strength
  • Decreased range of motion

Three types of muscle strains


There are three types of muscle strains: first-degree, second-degree, and third-degree.

Those who watch professional sports have probably heard of these types of strains but have yet to understand them fully. Well, we’ve got you covered here. The three types of strain, with the hamstring muscle used as an example.

Image of a muscle strain

First-degree (grade I) strain

A first-degree strain, also referred to as a grade I strain or mild strain, has the following characteristics:

  • Less than 5% of the fibers are torn
  • No significant loss of strength
  • Less than 10% loss in the range of motion
  • Can continue the sport or activity

Second-degree (grade II) strain

A second-degree strain, also called a grade II strain or a moderate strain, has the following characteristics:

  • Disruption of fibers and strength in the 5-50% range
  • Swelling and bruising can be present, unlike the first-degree strain
  • The person can no longer continue the activity
  • More than 10% loss of range of motion

Third-degree (grade III) strain


A third-degree strain, also known as a grade III strain, is the most severe type of muscle strain and has the following characteristics:

  • 50-100% disruption of fibers and strength
  • Moderate swelling and bruising
  • Loss of function
  • The muscle becomes retracted at the different ends

Causes and predisposing factors

Muscle strains are usually caused by a force overstretching the muscle or a violent contraction. This can occur from work, recreational activities, or activities of daily living. However, there is a condition called cumulative trauma resulting from the repetitive use of muscles or tendons. It is common in occupations such as factory workers and landscapers.

Some factors predispose people to muscle strain, making them more likely, including:

  • Not warming up the muscles with cardiovascular exercise to increase blood flow to the muscles.
  • An inflexible (rigid) muscle that is caused by a lack of stretching.
  • Muscle fatigue can lead to strain. For example, shoveling snow after a blizzard can strain the low back muscles.
  • Muscle imbalance is caused by a sport that relies more on one side of the body, such as baseball pitching, bowling, golf, tennis, or throwing a football.
Muscle strain can occur in any muscle of the body. Different sports, activities, and jobs lead to different injured muscles. Unfortunately, there's no data on which muscle is strained most often since it varies by sport, activity, and occupation.

Diagnosing a muscle strain

A history should be taken to ask questions about the muscle pain. The medical professional doing an examination should look for answers to questions such as:

  • When did it happen?
  • What were you doing when you first felt the pain?
  • Did you hear a loud pop?
  • Are there limitations with specific body movements?

A physical exam should examine for tenderness, swelling, strength, range of motion, and muscle retraction.

Imaging studies such as plain X-rays will allow the physician to view the underlying bones. However, a magnetic resonance imaging (MRI) test is the best diagnostic test to evaluate the muscles and tendons.

A laboratory test (bloodwork) that can be helpful is the creatine kinase level, an enzyme in a normal muscle that makes its way to the bloodstream. The creatine kinase can be elevated from widespread muscle damage. A serum calcium level should also be checked since low calcium levels lead to muscle cramps.

Treatment for muscle strains

  • Medications such as non-steroidal anti-inflammatories, muscle relaxers, and pain meds
  • Ice for the first 24 hours
  • Exercising and stretching
  • Chiropractic
  • Physical therapy (PT) and occupational therapy (OT)
  • Acupuncture

If you experience discomfort in specific areas, there are also ways to relieve lower back pain and stop pain in the neck.

Preventing muscle strains

There are some general ways to prevent muscle strain before engaging in any sport or activity:

  • Perform light aerobic activity before engaging in more strenuous sports or activities. Light aerobic activities include walking, cycling, swimming, or anything to get your "heart pumping."
  • Stretch lightly before any activity, and stretch moderately afterward.
  • Practice good posture. For example, if lifting boxes or shoveling snow, bear the weight with your legs and not your back.
  • Use caution in restarting the activity that caused the injury. If there is pain after restarting, then stop.

Muscle strains may seem painful and debilitating. However, with prompt diagnosis and treatment, symptom relief and healing can result.


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