A hamstring strain is an injury to the muscle fiber, tendon or muscle and tendon attachment point. It is common in athletes from ballet dancers to soccer players and sprinters. Of the three muscles that make up the collective hamstring muscles (biceps femoris, semimembranosus and semitendinosus) strain injuries occur in the biceps femoris over 75% of the time.

Mechanism of Injury :
A hamstring strain is classified as a type 1 or type 2 hamstring strain depending on the mechanism of the injury.

Type 1 acute hamstring strains are related to sprinting or heavy loading of the hamstring muscles and can be often found during sprinting, hurdling, jumping or kicking. The hamstrings most often become injured during the time right before the foot strikes the ground when an athlete is sprinting. At this stage of the leg swing cycle there is a great amount of force placed on the muscles as they are maximally activated and are approaching their maximum length while working eccentrically to rapidly slow the leg and control knee and foot movement.

Type 2 acute hamstring strains are considered stretch related injuries that are often seen in dancers or gymnastics.  These occur when the muscles are put into excessive stretch positions through hip flexion.  These injuries may feel less intense to the athlete than a type 1 strain but they may take longer to heal because of the location and type of injury to the muscle and tendon.  These injuries most likely occur in the semimembranosus muscle.

Risk factors for a hamstring strain: 

• Age: the older you are the more you are at risk for a strained hamstring.
• Previous Injury: Previous injuries to your hamstrings or adductor muscles can increase the risk of re-injury in the future.
• Flexibility: The greater the flexibility of your hamstrings the less prone they are to injury.
• Hamstring strength: Lack of hamstring strength is strongly linked to a chance of a pulled (strained) hamstring.
• Lumbosacral nerve impingement: Nerve impingement in your L5-S1 lower back bones can lead to related hamstring muscle weakness.
• Tiredness and fitness: When you are fatigued you lose coordination of muscle groups. The biceps femoris muscle is a hamstring muscle that has two separate nerves to help it work. When you are tired the nerves may not work together, you could pull your hamstring because one section is working while the other is not.
• Poor warm-up before explosive movements such as running, kicking, jumping

Signs and Symptoms:

• Immediate intense pain, “It felt like I was struck in the back of the leg”.
• Hamstring muscles going into spasm (related to pain when you stretch or use the muscle).
• Swelling and bruising.
• Decreased strength.

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On-Site Management:
P.R.I.C.E.

PROTECT the area from further injury by avoiding exercises that produce pain. A neoprene sleeve can be worn over the muscle to keep it warm during activity. Initially avoid weight bearing activity.

REST: cutting back on the amount of training can be difficult, but key to recovery. The key is gradually returning to any running activities through proper rehabilitation as monitored by a certified therapist.

Place ICE on your hamstring for 10-20 minutes every 1.5 to 2 hours for the first 2 to 3 days or until the pain goes away. Do not place the ice directly on the skin, place a compressive sleeve or wrap between the skin and the ice.

COMPRESS the area by having a trainer or physiotherapist use a compression wrap. This helps decrease swelling in the muscle.

ELEVATION is important to encourage blood flow to the heart to decrease swelling.

Medical Referral, Treatment and Rehabilitation:

 When there is a hamstring strain it is important that you seek medical attention to rule out a complete tear or referred pain from another injury. Seeing a physician or physical therapist as soon as possible is suggested as the physician may prescribe anti-inflammatory medication to help with pain and swelling as well as starting the patient on isometric, low-grade, pain free muscle activation exercises that have been shown promote healing in the hamstring. The therapist/physician individual can perform a proper evaluation of running/jumping biomechanics and footwear. The therapist can also work with the athlete to monitor treatment and guide in strengthening activities for return to play.  The return to play progression will include gradually building up running time and intensity along with active rehabilitation, stretching, functional/ sport specific movements, soft tissue treatment and massage, strengthening, and neuromuscular training.  This progression can range in time depending on the severity of the injury and compliance to treatment and rehabilitation. 

Return to Activity: 

This is a gradual process and may take some time. In general, the longer you have symptoms before you start treatment, the longer it will take to rehabilitate. The following is a list of guidelines to follow when returning to activity.

• Work towards full range of motion in the affected hamstring compared to the unaffected one.
• Work towards full strength of the affected hamstring compared to the unaffected one.
• Work towards jogging straight ahead without pain or limping.

Your therapist will also use more specific tests to determine when you can return to play.

Prevention:

• One of the most important ways to prevent a pulled hamstring is to warm up correctly and completely. Thermal pants and dynamic sport specific exercise warm ups are suggested to help with this.
• A specific strengthening program for your hamstring muscle group is important if you are a sprinter or compete in high speed athletics.
• It is extremely important to continue to strengthen all other muscles in the thighs, pelvis and lower back to make sure you have correct muscle balance.
• Stretching both before and after exercise.
• Regular deep tissue sports massage can help prevent muscle strains by identifying tight knots and weak points in the muscle.

Brukner, P. and Khan, K. Brukner and Khan's Clinical Sports Medicine Brukner, P. and Khan, K. (2007) Brukner and Khan's Clinical Sports Medicine. 4th ed. North Ryde: McGraw-Hill.

Contribution by: Andrea Bulat