Muscle Injury

Muscle injuries are among the most common soft tissue injuries, affecting everyone from professional athletes to people doing everyday activities. These painful tears in muscle fibers can range from minor stretches to complete ruptures, but most heal with proper rest and care.

Table of contents

• What Is a Muscle Injury
• How Muscles Work
• Types and Severity of Muscle Injuries
• What Causes Muscle Injuries
• Who Is at Risk
• Signs and Symptoms
• How Muscle Injuries Are Diagnosed
• Treatment Options
• Recovery and Healing

muscle strain, pulled muscle, muscle tear

What Is a Muscle Injury

A muscle strain, commonly called a pulled muscle, is an injury where muscle fibers are torn. This happens when a muscle is stretched beyond its normal limit or used too much, which weakens the fibers.^[1][2] Muscle injuries are one of the most common soft tissue injuries that people experience.^[2]

Skeletal muscle tissue makes up the largest mass in the human body, accounting for 45% of the total weight.^[3] Because muscles are so important for movement and everyday activities, injuries to them can significantly affect a person’s ability to function normally.

A muscle strain is different from a sprain. A strain involves injury to a muscle or the tissue that connects muscle to bone, while a sprain injures the bands of tissue that connect two bones together.^[1]

How Muscles Work

Muscles are made of thousands of small fibers woven together. These fibers work like a bungee cord—they have plenty of give and stretch when they’re healthy. But if you use them for too long or suddenly pull too hard, the fibers start to pull apart.^[2]

A muscle is surrounded by an outer covering that allows it to move smoothly over surrounding tissues when it contracts. Inside this outer layer are bundles of muscle fibers. These bundles are made up of even smaller units called myofibrils, which contain millions of microscopic units called sarcomeres that are responsible for muscle contraction.^[4]

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, causing a contraction. When the myosin proteins relax, the sarcomeres lengthen back to their original position and so does the muscle. This combination of muscle contraction and relaxation, coordinated through the nervous system, is what allows people to run, kick, throw, walk, and breathe.^[4]

Muscles connect to bones through tendons at each end. During activities that require explosive movements, such as pushing off during a sprint or changing directions quickly, the force across the muscle-tendon unit can be so great that tissues tear, either partially or completely.^[4]

Types and Severity of Muscle Injuries

Muscle injuries can be caused by bruising, stretching, or cutting.^[3] The severity of a strain depends on how much strength and range of motion a person loses, which also indicates how long it will take to recover.^[4]

Healthcare providers classify muscle strains into three grades based on severity:^[3][4]

• Grade 1 (Mild): This involves stretching and injury to the muscle fibers, but there is minimal structural damage. Only a few fibers are pulled and broken. The signs and symptoms include swelling (fluid in the muscle) and discomfort.
• Grade 2 (Moderate): More extensive damage with more muscle fibers involved, but the muscle is not completely torn. These injuries show loss of function, gaps in the muscle, and possible bruising under the skin. People experience significant loss of strength and motion.
• Grade 3 (Severe): Complete rupture of a muscle or tendon. These injuries involve complete tearing, severe pain, and extensive blood collection in the tissue. A person may be able to see or feel a gap or dent in the shape of the muscle.

Muscle strains are also classified by how they develop:^[2]

• Acute muscle strains: These happen suddenly and cause immediate symptoms. A person might pull a muscle with a sudden, forceful movement or by twisting it.
• Chronic muscle strains: These develop gradually, and so do the symptoms. A person can gradually tear a muscle by overusing it without giving it enough time to repair.

Common locations for muscle strains include the back, neck, legs (especially the hamstrings at the back of the thigh), calves, hip flexors, groin, and abdomen.^[1][2]

What Causes Muscle Injuries

Muscle strains occur when the force on a muscle is so great that the tissue is damaged. The injury can happen in one of three places: within the muscle itself, at the junction between the muscle and tendon (most common), or in the tendon where it attaches to the bone.^[4]

Muscle strain happens when a muscle is stretched too much, too quickly, or works too hard. Sudden or excessive forceful stretching while the muscle is contracting causes overstretching, which results in tearing of the muscle fibers.^[5]

Acute strains can be caused by one event, such as using poor body mechanics to lift something heavy. Chronic muscle strains can result from repetitive injuries when a person stresses a muscle by doing the same motion over and over.^[1]

Common causes include:^[2]

• Acute injuries: Muscle strains are often sports injuries caused by sudden sprinting, twisting, or jumping. Accidental muscle strains are also common in everyday life.
• Repetitive strain injuries: Repeating the same movement over and over, whether at work or during a recreational activity, can strain muscles over time.
• Overtraining: Training or working too hard or too long without letting muscles rest weakens them. If they don’t have a chance to rebuild, they might break instead.
• Undertraining: Low flexibility and strength can cause muscles to strain with ordinary use. Not stretching or warming up before exercise can put too much stress on muscles before they’re ready.

These injuries commonly occur during excessive loading of the muscle—that is, when the muscle is contracting while it is also lengthening.^[4]

Who Is at Risk

Some muscles are more likely to tear than others. These are muscles that cross more than one joint or that stretch and lengthen while bearing a load. Muscles that cross joints often act to restrain other muscles when a person moves that joint. If the joint moves with too much force, these muscles feel the impact first.^[2]

Muscles that cross two joints are the most susceptible to injury. These include the hamstrings (crossing the hip and knee joints), the calf (crossing the knee and ankle joints), and the quadriceps (crossing the hip and knee joints). The hip muscles used to pull the legs together (called groin muscles) are also commonly affected.^[4]

Participating in contact sports such as soccer, football, hockey, boxing, and wrestling can increase the risk of muscle strains.^[1] Muscle strains are one of the most common reasons for missed playing time in professional sports and currently the leading cause of missed playing time in the NFL. However, a person does not have to be a professional athlete to experience such an injury—they are quite common among both professional and recreational athletes.^[4]

Factors that can predispose a person 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 significantly increasing exercise load. That is why they are much more common during training camps than throughout the regular playing season.^[4]

Signs and Symptoms

Signs and symptoms vary depending on the severity of the injury.^[1] Common symptoms of a pulled or torn muscle include:^[2]

• Pain or tenderness
• Muscle pain
• Muscle spasms or tightness
• Bruising or redness
• Swelling
• Muscle weakness
• Limited motion or limited range of motion
• Feeling a “pop” during the injury
• Seeing a gap or dent in the shape of the muscle

A torn muscle feels sore when a person tries to use it. The pain can usually be located in one spot. A person may be able to connect it to a recent event or activity. If it’s a chronic muscle strain, pain may develop gradually over a few days. If it’s an acute muscle strain, pain is felt immediately, and it may even feel like tearing. The muscle may also weaken, and a person may feel that they can’t use it at all.^[2]

With a severe strain, a person will most likely hear an audible pop and see a dent in the outline of the muscle. They’ll feel immediate pain, swelling, tenderness, and weakness, and might eventually have bruising.^[12]

Mild strains can be treated at home. However, a person should see a doctor if symptoms worsen despite treatment, especially if pain becomes unbearable or if they experience numbness or tingling.^[1] Medical help should be sought right away if there is a lot of swelling with the muscle strain, if joints cannot be moved, or if swelling is getting worse as time passes.^[13]

How Muscle Injuries Are Diagnosed

During a physical exam, a doctor will check for swelling and points of tenderness. The location and intensity of pain can help determine the extent and nature of the damage. In more severe injuries where the muscle or tendon has been completely ruptured, a doctor may be able to see or feel a defect in the area of injury.^[8]

Physical examination includes inspection and palpation. Tenderness when touched is felt in the injured area. The doctor examines the area close to where the muscle starts (its origin), the muscle belly, and the area where it attaches.^[5]

The diagnosis can be confirmed with imaging tests:^[3][5]

• Ultrasound: This test is dynamic and inexpensive, but depends on the examiner’s skill. It often can help distinguish among several different types of soft tissue injuries.^[8]
• Magnetic Resonance Imaging (MRI): This provides better anatomical definition and clearer pictures of the injury.
• X-rays (Radiographs): These are indicated only if there is concern for an associated fracture.^[5]

Treatment Options

For immediate self-care of a muscle strain, the R.I.C.E. approach is recommended—rest, ice, compression, and elevation:^[8]

• Rest: Avoid activities that cause pain, swelling, or discomfort. However, don’t avoid all physical activity. Rest the strained muscle and do not put weight on it for a day or two.^[16]
• Ice: Even when seeking medical help, ice the area immediately. Use an ice pack or slush bath of ice and water for 15 to 20 minutes each time and repeat every two to three hours while awake for the first few days after the injury. Put ice or a cold pack on the sore area for 10 to 20 minutes at a time, every 1 to 2 hours for the next 3 days. Place a thin cloth between the ice and skin.^[16]
• Compression: To help stop swelling, compress the area with an elastic bandage until the swelling stops. Don’t wrap it too tightly or circulation may be hindered. Begin wrapping at the end farthest from the heart. Loosen the wrap if pain increases, the area becomes numb, or swelling occurs below the wrapped area.
• Elevation: Elevate the injured area above the level of the heart, especially at night, which allows gravity to help reduce swelling. Prop up the sore arm or leg on a pillow when icing it or anytime sitting or lying down during the next 3 days.^[16]

The initial phase of treatment consists of protection, rest, optimal use of the affected limb, and cooling therapy.^[3]

Additional treatment approaches include:^[3][8][13]

• Pain medications: Over-the-counter medications such as acetaminophen (Tylenol), ibuprofen (Advil, Motrin), or naproxen (Aleve) can provide pain relief, unless a doctor has advised against taking these medicines. Anti-inflammatory medicines such as ibuprofen and naproxen also help reduce swelling. Some doctors recommend avoiding pain medications that can increase the risk of bleeding during the first 48 hours after a muscle strain.
• Heat therapy: After 2 or 3 days, heat can be applied to the area that hurts. Apply heat for 10 to 20 minutes at a time, several times a day. Alternating between ice and heat can also be tried.^[16]
• Physical therapy: A physical therapist can help maximize the flexibility and strength of the muscle and teach exercises to improve healing.
• Stretching and exercise: After pain resolves, gently stretch and exercise the muscle as this can help strengthen it.^[5] Gentle stretching promotes healing by re-establishing the normal length of the muscles. However, overstretching should be avoided. Stretching and light exercises to bring blood to the injured area can also be useful. As the pain decreases, heat can be used on the muscle.^[13]
• Range of motion exercises: These should be done without pain after the initial phase.

Surgery has precise indications: draining blood collection in the tissue and reattaching and reinforcing the muscle-tendon unit.^[3] Severe strains sometimes require surgical repair. If a person has severe muscle pain, they should see a doctor right away, as they might need to immobilize the injured muscle or have it repaired surgically if it has been torn.^[1][12]

Recovery and Healing

Most muscle strains are painful, but they can heal with time and rest.^[2] Mild strains can be successfully treated at home.^[1]

Less severe strains can be mistaken for sore muscles initially, since both can be tender and painful. The main differences are in location and healing time. If pain is in a large area, such as the entire back, it’s probably due to sore muscles responding to new activity. If pain is localized to one specific area, it’s likely a strain. If pain eases by day three, it’s probably just sore muscles. If pain intensity has increased by day three, it’s probably a strained muscle.^[12]

After 2 days of home treatment, if pain and swelling get worse or do not start to get better, a person should contact their doctor.^[16] Follow-up care is a key part of treatment and safety. People should be sure to make and go to all appointments and call their doctor if they are having problems.^[16]

Return to exercise should be gradual as a person feels better.^[16] A person should not do anything that makes the pain worse and should avoid movements or activities that can reproduce pain.^[5]

Getting enough sleep is important during recovery, as this is when the body rebuilds and repairs itself.^[12]