What Is a Muscle Strain?

Often referred to as a “pulled muscle,” a muscle strain is actually a partially or completely torn muscle.

Muscle strain injuries occur most often:

• in muscles that cross two joints
• during explosive action, such as sprinting
• during times when athletes suddenly increasing their exercise regimens (such as during training camps)

What Causes a Muscle Strain?

A muscle strain happens when a muscle is stretched beyond its usual range of motion and begins to tear. These injuries occurs most often at the junction between the muscle and the tendon. However, a muscle strain can also occur within the muscle itself or in the tendon, where it attaches to the bone.

Muscles are often called our body's building blocks. Tendon attachments at each end of each muscle work together to provide the force required for movement. During activities that require explosive movements, like pushing yourself up during a squat or changing directions quickly in racquetball, too much force can tear connective tissue either partially or completely through.

Injuries commonly occur when the muscle becomes overworked and is stretched back further than is safe. Both the quadriceps, which involve the knee and hip, and the hamstrings, which involve both the hip and knee as well as parts of the ankle, are most prone to injury. Muscle strains in the hip adductor muscles are also common, even though they only cross the hip joint.

These factors can predispose an athlete to muscle strain injuries:

• older age
• previous muscle injury
• less flexibility
• lack of strength in the muscle
• fatigue

Signs and Symptoms of a Muscle Strain

The symptoms of a muscle strain are: 

• sharp, “stabbing” pain that worsens while contracting the muscle
• swelling and bruising
• loss of muscle strength 
• reduced range of motion 

Significant inflammation occurs when muscle is first injured. Then stem cells that live around the area of injury begin to regenerate muscle fibers, which aids the healing process.

When a muscle is injured, it goes into the inflammatory stage. This phase is marked by the beginnings of an immune system response following the injury and begins to repair the damage done to that muscle. But one significant thing that happens during this phase is that a great deal of scar tissue forms in that area of injury. Scar tissue isn't just fibrous, it's dense—and doesn't stretch and contract in the same way. Over time, this scar tissue begins to remodel into actual fibers with proper alignment, though they are far less elastic than healthy muscle fibers. It's thought that as a result of this type of remodeling a strained muscle becomes prone to further injury much more easily because of its structural weakness.

How Is a Muscle Strain Diagnosed?

Physical Exam

In most cases the diagnosis of a torn tendon is made based upon the patient's medical history and physical exam. In rare, grade 3 cases, the physician can actually feel the defect where the muscle has completely torn during an examination.

X-Rays

When patients come to the hospital with an indication of having a muscle injury, it is frequently difficult and/or costly to determine what the cause is without further investigative methods. Standard X-rays are beneficial in assessing fractures and dislocations. Occasionally in younger athletes, the tendon can pull off a piece of bone where it attaches, which can be seen on standard X-rays. However, simple muscular injuries cannot be seen on regular X-rays. 

MRI

MRI's can sometimes be helpful in determining where the injury has occurred and whether it's a complete rupture or not. MRIs also show collections of blood called hematoma that sometimes occur following severe injuries.

Treatment for Muscle Strain

Conservative, nonsurgical treatment

The majority of muscle strains do not require surgery, and a full recovery is expected. If there is only a partial tear, then the athlete can return when they have stopped feeling pain during normal activity and have normal strength/flexibility in the affected area. A complete rupture means that an injured athlete may benefit from surgical repair.

Most acute muscle injuries are partial thickness tears (rather than complete tears). These cases can often be treated successfully with 

• the RICE protocol (rest, ice, compression, elevation).
• NSAIDs - nonsteroidal anti-inflammatory drugs (such as ibuprofen)

After a week of these at-home treatments, many patients benefit by progressive functional physical therapy. The good news is: Most athletes are able to return to their previous level of competition after a muscle strain is fully healed. The bad news is: Since scar tissue forms at the site of injury, they may susceptible to another injury at that location.

Surgery and platelet-rich plasma injections

Complete muscle injuries can lead to considerable functional impairment, short-term and long-term 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. Platelet-rich plasma (PRP) injections may be able to help accelerate the regeneration of damaged muscle tissue. Although there are other treatments available for complete muscle injuries, PRP might prove especially useful for patients who must either be able to run or demonstrate sufficient agility to play sport, because this population tends to recover slowly from such injuries.