Muscle Strain: Causes, Symptoms, Treatment

What is a muscle strain?

Muscle strain or a "pulled muscle" is an injury that causes stretching of the muscle fibers and can lead to a partial or complete tear of a muscle.

These injuries typically occur:

• in muscles that cross two joints
• during explosive action, such as sprinting
• during times when athletes are suddenly increasing their exercise regimens or when the muscle is over fatigued (such as during training camps)

Normal muscle anatomy and function

A muscle is surrounded by an outer sheath that allows it to move smoothly over the surrounding tissues as it contracts. Inside the outer sheath are bundles of muscle fibers known as fascicles, which are further made up of myofibrils. These myofibrils are composed of millions of microscopic units called sarcomeres that are responsible for muscle contraction. In the sarcomere, muscle proteins called myosins pull against thin ropes of protein called actin when they are stimulated by nerves. When this occurs, the sarcomeres shorten, resulting in a contraction. When the myosin proteins relax, the sarcomeres lengthen back to their original position and so does the muscle.

The combination of muscle contraction and relaxation is coordinated through the nervous system. This is what allows athletes to run, kick, throw, and, for that matter, even walk and breathe.

What causes muscle strains?

Muscle strains occur when the force on a muscle is so great that the tissue is damaged.

The injury can occur in one of three places:

• within the muscle itself
• at the junction between the muscle and tendon (most common)
• in the tendon, where it attaches to the bone

Muscles, by way of their tendon attachments at each end, insert into bones and provide the force required for movement. During activities that require explosive movements, such as pushing off during a sprint or changing directions in cutting sports, the force across the musculotendinous unit (the connected muscle and tendon) can be so great that tissues tear, either partially or completely.

These injuries commonly occur during excessive loading of the muscle; that is, when the muscle is contracting while it is elongating. Muscles that cross two joints, such as the hamstrings (the hip and knee joints), the calf (the knee and ankle joints), and the quadriceps (the hip and knee joints) are the most susceptible to injury. The hip adductor muscles (so called groin strains) are also commonly affected, though most of those muscles only cross the hip joint.

Factors that can predispose an athlete to injury include older age, previous muscle injury, less flexibility, lack of strength in the muscle, and fatigue. Muscle strains occur more commonly when the muscle is not adequately adapted to the demands of the activity such as starting a new sport or significant increases in exercise load. That is why they are much more common in training camps in the NFL than they are throughout the regular playing season.

Are there different types of muscle strain?

The severity of a strain can be assessed by how much strength and range of motion a person loses, and this can also provide an idea as to how long it will take to recover. Muscle strains can be categorized into three grades, based on severity:

• Grade 1 – Stretching and injury to the muscle fibers, but there is minimal structural damage. This is characterized by edema or fluid in the muscle on MRI.
• Grade 2 – More extensive damage with more muscle fibers involved, however, the muscle is not completely ruptured. These injuries present with significant loss of strength and motion.
• Grade 3 – Complete rupture of a muscle or tendon. These can present with a palpable defect in the muscle or tendon. However, swelling in the area may make this difficult to appreciate. These injuries sometimes require surgery to reattach the damaged muscle and tendon.

It is important to note that this grading system can give some guidance as to healing time. Grade 1 injuries can take just as long as grade 2 injuries to heal.

What are the signs and symptoms of muscle strain?

The key symptoms of a muscle strain include sudden pain that worsens while contracting the muscle, swelling and bruising, loss of strength and range of motion. People often report the sensation of pain as the feeling of being kicked or hit with something. When muscle is initially injured, significant inflammation and swelling occurs.

After this inflammatory phase, the muscle begins to heal by regenerating muscle fibers. However, a significant amount of scar tissue also forms where the muscle was injured. Over time, this scar tissue remodels, but sometimes the muscle tissue never fully regenerates. It is thought that this makes a strained muscle prone to future injury.

How is a muscle strain diagnosed?

The diagnosis is almost always made based on patient history and physical exam. In severe, grade 3 cases, the examining physician may be able to feel the defect where the muscle has completely torn.

An X-ray may be helpful to rule out a fracture or dislocation as the cause of pain. Occasionally in young athletes, the tendon can pull off a piece of bone where it attaches, which can be seen on X-rays.

However, pure muscle injuries cannot be seen on regular X-rays. While a muscle injury can only be seen on MRI, advanced imaging is often not necessary in the clinical setting as it often doesn’t change care. The exception to this is when a grade 3 injury is suspected that may require surgery.

What is the treatment for a muscle strain?

Most muscle strains do not require surgery and will heal on their own with appropriate time. The following treatments are typically used:

• Avoiding activities that cause pain and may further injury the muscle.
• Physical therapy to regain strength and function.
• Giving adequate time for the muscle strain to heal. Returning too soon can lead to re-injury.

If there is a partial tear, then the athlete can return when they are pain free and have normal strength and motion. This usually occurs following anywhere from a few weeks to a few months of appropriate treatment and therapy. When the tendon is completely ruptured, the athlete may benefit from surgical repair.

The majority of acute muscle injuries are partial thickness tears. These can most often be treated successfully with:

• the RICE protocol:
  • rest
  • ice
  • compression
  • elevation
• Offloading the muscle may be useful in the acute period. For hamstring strains for example, crutches may be useful for the first few days or a couple of weeks.

These treatments will be done for the first week or two, followed by progressive functional physical therapy, as needed.

While the use of anti-inflammatory medication can be helpful to control pain, there is no convincing data that NSAIDs (nonsteroidal anti-inflammatory drugs) improve healing or decrease time to return to play. There are actually some small studies that suggest NSAIDs may impede healing in the acute injury setting.

If there is a partial tear, then the athlete can return when they are pain free and have normal strength and motion. This usually occurs following anywhere from a few weeks to a few months of appropriate treatment and therapy. When the muscle is completely ruptured, the athlete may benefit from surgical repair.

Many athletes are able to return to their previous level of competition, but since scar tissue forms at the site of injury, they may be susceptible to another injury at that location.

Other interventions

As muscle strains are one of leading causes of missed playing time in professional sports, there is a lot of research that goes into finding other interventions to decrease healing time. As of the current literature, there is no clear intervention that can speed up healing time or decrease the time to return to play.

If the injury results in a large hematoma (a collection of the blood within the muscle), there are studies that show aspiration (removing the blood through a needle) of the hematoma can help with pain and may decrease healing time.

The use of corticosteroid injections in acute muscle injuries is controversial. While they can temporarily help with pain, there isn’t evidence to suggest improved healing. There may be some benefit in their use in fascial injuries (injuries to the connective tissue between muscle bundles).

The use of platelet-rich plasma has become increasingly popular. PRP is obtained by spinning a patient’s blood to obtain a concentrated sample that has a higher concentration of platelets. There were initially some small studies that showed benefit to use of PRP specifically in vitro studies. However as more robust research has been done, it is unclear if PRP significantly decreases healing time or time to return to play in acute muscle injuries. There are some small recent studies that may show benefit of the use of platelet-poor plasma (PPP) in acute muscle injuries, but more research is needed to know for sure.

Complete muscle injuries can lead to significant functional impairment and lost playing time and may require surgical repair. This is especially the case for patients who need to be able to run or be sufficiently agile to participate in sport.

When can I return to sports after muscle strain?

Return to full activity is usually allowed when the patient is pain free, has full range of motion, and full strength. If an athlete attempts to return to their sport before these criteria are met, there is a high chance of reinjuring the muscle and sustaining a setback. While each injury is individual, in general it takes weeks to months for these injuries to heal adequately. Data would suggest that returning to sport before 4 to 6 weeks leads to an increased risk of injury. More severe injuries can even take 4 to 6 months to resolve.

Such a long period of lost playing time is less than ideal for professional and elite athletes, and some have advocated more aggressive treatment in this group. Unfortunately, most of the interventions study have yet to show convincing evidence of decreasing time to return to play. Research is ongoing, so who knows what the future may hold. There are some studies in hamstring strains that show incorporating an eccentric loading program in the offseason may decrease the rate of injury.

Updated: 6/17/2024

Authors

Related articles

References

• Drakos M, Birmingham P, Delos D, Barnes R, Murphy C, Weiss L, Warren R. Corticosteroid and Anesthetic Injections for Muscle Strains and Ligament Sprains in the NFL. HSS J. 2014 Jul;10(2):136-42. doi: 10.1007/s11420-014-9395-7. Epub 2014 May 21. PMID: 25050097; PMCID: PMC4071464.
• Koscso JM, McElheny K, Carr JB 2nd, Hippensteel KJ. Lower Extremity Muscle Injuries in the Overhead Athlete. Curr Rev Musculoskelet Med. 2022 Dec;15(6):500-512. doi: 10.1007/s12178-022-09786-z. Epub 2022 Aug 1. PMID: 35913667; PMCID: PMC9789236.
• Halpern BC, Chaudhury S, Rodeo SA. The role of platelet-rich plasma in inducing musculoskeletal tissue healing. HSS J. 2012 Jul;8(2):137-45. Doi: 10.1007/s11420-011-9239-7. Epub 2012 Jan 18. PMID: 23874254; PMCID: PMC3715623.
• Biz C, Nicoletti P, Baldin G, Bragazzi NL, Crimì A, Ruggieri P. Hamstring Strain Injury (HSI) Prevention in Professional and Semi-Professional Football Teams: A Systematic Review and Meta-Analysis. Int J Environ Res Public Health. 2021 Aug 4;18(16):8272. doi: 10.3390/ijerph18168272. PMID: 34444026; PMCID: PMC8394329.
• Rudisill SS, Varady NH, Kucharik MP, Eberlin CT, Martin SD. Evidence-Based Hamstring Injury Prevention and Risk Factor Management: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Am J Sports Med. 2023 Jun;51(7):1927-1942. doi: 10.1177/03635465221083998. Epub 2022 Apr 6. PMID: 35384731.
• Sheth U, Dwyer T, Smith I, Wasserstein D, Theodoropoulos J, Takhar S, Chahal J. Does Platelet-Rich Plasma Lead to Earlier Return to Sport When Compared With Conservative Treatment in Acute Muscle Injuries? A Systematic Review and Meta-analysis. Arthroscopy. 2018 Jan;34(1):281-288.e1. doi: 10.1016/j.arthro.2017.06.039. Epub 2017 Aug 8. PMID: 28800920.

(Return to top.)