The hamstring muscle group includes 3 muscles along the back of the thigh that connect the pelvis to the leg. They are the primary muscle group responsible for straightening (extending) the hip and bending (flexing) the knee. The 3 muscles are:

• Semitendinosus.
• Semimembranosus.
• Biceps femoris.

The anatomy of muscles includes the muscle “belly,” the portion that contracts or relaxes to move a limb, and the tendon, the portion that connects the muscle belly to the bone. Hamstring strain injuries occur when there is damage to the muscle belly caused by excessive force being generated while the muscle is being stretched. This typically happens during high-speed running, with sudden starts or changes in direction, or when the muscle is overstretched by activities such as sprinting, hurdling, kicking, or heavy lifting.

Risk factors for hamstring strain injuries include:

• A history of prior hamstring strain injury.
• Hamstring weakness.
• Increasing age.
• Poor flexibility of the quadriceps and hip flexors (muscle tightness).
• Inadequate warm up before activity.
• Muscle fatigue.

When a person experiences a hamstring strain injury, a sudden onset of pain is felt in the back of the thigh. It happens very quickly and causes the individual to stop performing an activity. The symptoms caused by a mild injury may only last for a few days; symptoms of a more severe injury can last for weeks. Common symptoms include:

• A sudden, sharp pain in the back of the thigh or in the buttocks.
• A feeling of a "pop" or tearing in the muscle.
• Bruising within hours or days after the injury.
• Tenderness to touch in the affected area.
• Difficulty sitting comfortably, lifting the leg when lying down, or straightening the knee.
• Difficulty walking or running, resulting in a limp.

Diagnosis of a hamstring strain injury starts with a thorough understanding of your health history and the cause of the injury. The questions your physical therapist may ask include:

• What were you doing when you first felt the pain, and did you feel a “pop"?
• Where do you feel the pain now?
• Did you notice any bruising after the injury?
• What were you not able to do immediately following the injury, and how have you been functioning since the injury (eg, walking, sleeping, lifting your leg)?
• Have you had a similar injury before?

Your physical therapist will also perform a clinical evaluation, including some of the following tests and measures to determine the nature of your injury:

• Observation, to note any discoloration or bruising.
• Pain assessment, to identify your current pain level, and the activities that make your pain better or worse.
• Palpation (gently pressing with the fingers), to pinpoint the location and size of the tender area through touch, which will help determine the severity of the injury.
• Range-of-motion test, to compare the motion of your injured leg with your healthy leg.
• Muscle-strength test, to determine the strength of the hamstring muscles when bending or straightening your knee and hip.
• Gait analysis, to note any limping or changes in how you are walking.

Typically, hamstring strain injuries are classified as Grade I, II, or III depending on the severity of the injury:

• Grade I: Mild strain with minimal tearing; usually feels like a pulled or cramping muscle.
• Grade II: Moderate strain with partial tearing; may cause a stinging or burning sensation at the back of the thigh.
• Grade III: A severe, complete muscle tear; may result in a “lump” on the back of the thigh where the muscle has torn.

If your physical therapist suspects a severe injury (Grade III), you will likely be referred to an orthopedic physician for medical diagnostic imaging, such as an X-ray or MRI, to evaluate the extent of the injury. In the event of a fracture of the ischial tuberosity (the “sit-bone,” part of the pelvis) and/or a complete rupture of the muscle, surgery may be recommended.

Immediately after experiencing a hamstring strain injury, seek help from a physical therapist. Prior to your physical therapy session, you can:

• Rest the injured area by avoiding aggravating activities, such as walking or working out. If you are having notable difficulty walking, you may need crutches. Do not overstress the injured area.
• Apply ice to the injured area 3 to 4 times a day for 15 to 20 minutes (with a towel placed between your skin and the ice).

Your physical therapist will design an individualized treatment program specific to the exact nature of your injury and your goals. Your treatment may include:

Manual therapy. Physical therapists are trained in manual (hands-on) therapy to gently move and manipulate muscles and joints to improve motion, flexibility, and strength. Your physical therapist may gently massage and move the affected area to encourage healing. These techniques can target areas that are difficult to treat on your own.

Range-of-motion exercises. Although it is common for your hamstring muscles to feel stiff after an injury, it is important not to stretch these muscles early in the recovery process. Your physical therapist will indicate when it is safe and appropriate to begin gentle flexibility exercises, and will guide you through how to do them in the clinic and at home.

Muscle strengthening exercises. Hamstring strengthening will be an essential part of your rehabilitation program. Your physical therapist will compare the strength of the muscle groups in each leg, and prescribe and teach you specific exercises to target areas of weakness.

Functional training. As you regain the strength in your hamstrings, your movement quality will need to be assessed so you no longer put excessive stress on the previously injured area. Your physical therapist will develop a functional training program for the hamstring muscle group, with a gradual progression back to more demanding activities.

In the event that the severity of your hamstring strain injury requires surgical treatment, a physical therapist will guide your postoperative rehabilitation. Your physical therapist will communicate with your surgeon to ensure complete and consistent postoperative care.

You can decrease your risk of a hamstring strain injury in the following ways:

• Always warm up before participating in athletic activities.
• Avoid starting a new activity too quickly; gradually increase the frequency and intensity of the activity so that your body may adapt to the new movement patterns.
• Maintain the strength of your hamstring muscles.
• Listen to your body after you work out (and stretch, apply ice, rest as needed) prior to engaging in the same routine again.

All physical therapists are prepared through education and experience to treat hamstring strain injuries. However, you may want to consider:

• A physical therapist who is experienced in treating people with hamstring strain injuries. Some physical therapists have a practice with an orthopedic or sports rehabilitation focus.
• A physical therapist who is a board-certified clinical specialist or who completed a residency or fellowship in orthopedics or sports physical therapy. This physical therapist has advanced knowledge, experience, and skills that may apply to your condition.

You can find physical therapists who have these and other credentials by using Find a PT, the online tool built by the American Physical Therapy Association, to help you search for physical therapists with specific clinical expertise in your geographic area.

General tips when you're looking for a physical therapist (or any other health care provider):

• Get recommendations from family, friends, or other health care providers.
• When you contact a physical therapy clinic for an appointment, ask about the physical therapists' experience in helping people with hamstring strain injuries.
• Be prepared to describe your symptoms in as much detail as possible, and report activities that make your symptoms worse.