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Hamstring Injuries


Hamstring injuries are one of the most common strains to affect athletes and the most common type of strain to affect the lower extremity. Hamstring strains can also be one of the most disabling injuries to the lower extremity.  These strains are most common amongst athletes that participate in sports that involve a lot of acceleration, deceleration, kicking, jumping, cutting, and pivoting. - sports such as soccer, rugby, football, and raquet sports.

How do hamstring injuries occur
Factors that predispose an athlete to hamstring strains
Recurrence of hamstring strains
Where do hamstring strains occur
Physiology of injuries to the hamstrings 
What does a hamstring injury look like
Classification of injuries
Treatment of hamstring problems
Is Dynamic or Static Stretching Better for Hamstrings?
Will Stretching Prevent Strains in Hamstrings?
How Does Dynamic Stretching Affect Previously Injured Athletes?

hamstring injuries

How do hamstring injuries occur

As with most muscle strains, the hamstrings are most commonly strained during an eccentric contraction. Eccentric contractions involve the lengthening of a contracting muscle. Hamstring strains are usually caused by a forceful hip flexion while the hamstring is working to slow the extension of the knee as in kicking or running.The hamstrings contract eccentrically during running to decelerate the forward movement of the tibia.   The hamstrings then change their role to extend the hip. It is at this point in running when the hamstrings go from contracting eccentrically to concentrically that the hamstrings are most vulnerable to injury.
What makes the hamstring particularly susceptible to injuries is the fact that the role of the hamstrings can change quickly many times during a task:
  • hip extension
  • deceleration of knee extension
  • knee stabilization
  • pelvic stabilization
All of these performed rapidly and repeatedly results in intense loading of the elongated hamstrings.

It is theorized that because the two heads of biceps femoris are innervated by two different nerves that there may be mistiming of contractions leading to a reduction in force produced with rapid eccentric contractions.
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Factors that predispose an athlete to hamstring injuries

It is thought that some of the following may predispose an individual to a hamstring injury:
  • Fatigue     In animal studies fatigued muscles have been shown to absorb less energy early on in a stretch compared to muscles that are not fatigued. Viscoelastic properties of fatigued muscles are different such that fatigued muscles are less elastic.
  • Lack of Flexibility  Reductions in hamstring flexibility has been shown to be correlated to injury. The emphasis amongst trainers to warm up adequately is evidence of this awareness. Muscles that are regularly stretched are more able to increase in length prior to tearing.
  • Prior Injury            Evidence of a recent hamstring injury has been shown to predispose an individual to future hamstring and quadricep injuries. Several studies (sited below) have shown correlation between pre season tightness of the hamstrings and hamstring injury during games in soccer players, and sprinters.
  • Weakness        Hamstring injury is associated with weakness in the hamstrings and weakness in hamstrings relative to the quadriceps. A balance between the knee extensors and flexors results in a more stable joint with less risk of injury. It is commonly thought that the hamstrings should produce >60% of the force put out by the quadriceps.
  • Poor lumbar posture   Excessive lordosis of the lumbar spine puts hamstring and gluteal muscles at a mechanical disadvantage. 
  • Poor core stability     Poor control over lumbar positioning forces the hamstrings to work inefficiently.
  • Inadequate warm up     A cold or inadequately warmed up muscle is stiffer and therefore more prone to tearing.  As muscles increase in temperature they become less viscous and more elastic.
  • Older Age
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Recurrence of hamstring injuries

Hamstring injuries have almost double the rate of recurrence when compared to other injuries in sports.(1,2,3,4) In football, studies show 12% of hamstring injuries will recur; whereas 7% is the recurrence rate of other football injuries.
Animal research has shown that previous strains leaves the muscle more prone to injury. Recurring hamstring strains have definitely been a challenge in the clinic.
One reason for recurrence is the presence of scar tissue. Scar tissue does not possess the  elastic properties of normal contractile and connective tissues of a healthy muscle. The scar does not stretch as easily and is therefore more susceptible to strain.
Another reason for recurrences is a failure to fully rehabilitate the injury. Disuse for even a short period can lead to weakness in other muscle groups and stiffness.
Although the most common period of reinjury is within a week of returning to sport, the risk remains for several weeks after healing has taken place. Players in my clinic are often anxious to return to their sport and I'm often forced to discourage them.
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Where do hamstring injuries occur

The hamstrings make up the bulk of the muscle in the back of the thigh. They consist of the bicep femoris, semitendinosus, and semimembranosus. They function as extensors of the hip, flexors of the knee, and rotators of the tibia on the femur when the knee is flexed.

                                          Origin           Insertion                   Innervation
Semimembranosus ischial tuberosity medial tibial condyle tibial nerve
Semitendinosus ischial tuberosity pes anserine insertion tibial nerve
biceps femoris (long head) ischial tuberosity head of fibula tibial nerve
biceps femoris (short head) linea aspera near head of femur head of fibula common fibular nerve

The most common site of injury is at the musculotendinous junction of the long head of the biceps femoris. The muscles of the body that cross more than one joint are often those that are most susceptible to injury.
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Physiology of hamstring injuries

As muscle fibres tear the body initiates an inflammatory response. Tears are often accompanied by bleeding as evidenced by ecchymoses present. The scar that the body uses to heal this tear is initially very weak, accounting for the high rate of recurrence and the fact that healing takes place over such a long period of time.

What does a hamstring injury look like

People that experience a hamstring injury will say that it felt like someone kicked them  in the thigh. There is often a sudden weakness and pain in the back of the thigh. There is swelling, pain with resisted flexion of the knee, occasionally a defect in the muscle, usually ecchymoses, and limited range of motion with a straight leg raise.
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Classification of hamstring injuries

Grading of a hamstring injury is based on the degree of damage done to the muscle.
  • Grade I      Over stretching of the muscle results in tearing of a few muscle fibres an inflammatory response, but no loss of strength or function. 
  • Grade II     Over stretching and tearing of the muscle results in loss of function and strength.
  • Grade III    Complete rupture of the muscle results in severe weakness. This is a rare occurrence and is most often found in water skiers.
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Treatment of hamstring injuries

Physical therapy for hamstring injuries is based on the muscles healing response.  Studies have shown that a program that includes trunk stabilization exercises reduces the rate of reinjury. (5,6) The goal of rehabilitation is to restore function in the shortest time possible while facilitating healing to minimize the chance of recurrence.
  1. Surgery may be indicated in the case of a complete avulsion of the proximal tendon or in the case of an avulsion fracture, but most strains can be treated with physiotherapy. 
  2. The use of non steroidal anti inflammatory medications such as naproxen and ibuprophen has been placed under scrutiny lately as it has been found to slow healing and affect the tensile strength of healing tissues.
  3. The obvious first aid response is R.I.C.E. (rest, ice, compression, and elevation) It is also of benefit, when applying the ice to apply it with the knee in a position of extension as tolerated. This helps to reduce further bleeding, control inflammation,  slow tissue damage, and control pain.
  4. Physiotherapy will often include the use of ultrasound to facilitate healing and improve the tensile strength of the healing musculotendinous unit.
  5. Early motion helps to  minimize scar tissue formation, and promotes healing.
  6. Early strength work should begin gently and done under advice of a physical therapist.
  7. Most hamstring injuries require two weeks of rest prior to returning to practice and often take several weeks to allow for return to full function. This depends of course on the extent of tissue damage, pain tolerance, and other individual factors (ie smoker, diabetes, etc) For several months the risk of reinjury can remain high even in the absence of symptoms.
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Is Dynamic or Static Stretching Better for Hamstrings

Your goals of hamstring stretching will determine what type of stretching is best for you. If you are looking to increase flexibility of your hamstrings because you need an increased range of motion for activities such as yoga, running hurdles, as a hockey goalie, or for dancing, then that appears best achieved through a program of static stretching when you are not practicing.

Bandy et al (7) in a study published in the Journal of Orthopaedic ans Sports Physical Therapy looked at the effects of static stretching, dynamic stretching, and no stretching on hamstring flexibility.

58 people ranging in age from 21 to 41 performed the following stretching protocols over a course of six weeks:

  1. One group performed dynamic stretching five days a week for a total stretch time of 30 seconds per bout of stretching.
  2. The other group performed a 30 second static stretch once a day for five days.
  3. The control group didn't stretch.
Results followed:
  1. Both dynamic stretching and static stretching increased hamstring flexibility.
  2. A 30 second static stretch was more effective than a 30 seconds of dynamic stretching in improving hamstring flexibility.
  3. A 30 second static stretch over 6 weeks resulted in more than twice the gain in range of motion when compared to dynamic stretching.

Will Stretching Prevent Hamstring Injuries?

A study by Pope et al published in Medicine and Science
in Sports and Exercise
examined male army recruits to determine if static stretches reduce the risk of injury.(8) It was found that static stretches didn't  result in a clinically meaningful reduction in the rate of injuries.

In this research the greatest predictor of injury was  poor aerobic fitness. It is thought that static stretching will not reduce injuries for the following reasons:
  • Some activities don't benefit from increased range of motion.
  • Stretching won't effect muscle elasticity during eccentric activities which is when most injury occurs.
  • Stretching may cause microtrauma in the muscle predisposing it to injury.
  • An increased in stretching tolerance after static stretching can mask pain that would normally cause muscle guarding during an activity that would cause injury.
According to a study done in 1999 (9) dynamic stretching prior to an explosive activity will reduce the likelihood of having an injury.
  • This is probably because the dynamic stretching will permit muscles to tolerate the stresses of the particular sport with less strain.
  • The specific dynamic stretches used will prepare the central nervous system for necessary activation of motor units and the necessary coordination.
  • Rates of injury may be less because practicing the movement patterns will help eliminate the awkward and inefficient movements.

1.  Witvrouw E, Daneels L, Asselman. Muscle flexibility as a risk factor for developing muscle injuries in male professional soccer players: a prospective study. Am J Sports Med Jan 2003:31;1: p 41-6

2. Jonhagen S, Nemeth G, Eriksson E. hamstring injuries in sprinters: the role of concentric and eccentric hamstring muscle strength and flexibility. Am J Sports Med. March 1994:22:262-265

3. Orchard JW. Intrinsic and Extrinsic Risk Factors for muscle strains in Australian Football. Am J Spots Med, May 2001 :29;3 p300 Garrett W. Muscle Strain Injuries. Am J Sports Med, Nov 1996 v 24:6;p32

4. Woods C, Hawkins RD, Maltby S, Hulse M, Thomas A, Hodson A. The football association medical research programme: An audit of injuries in professional football – analysis of hamstring injuries. Br J Sports Med 2004;38:36-41.

5. Zuluaga M, Briggs C, Carlisle J, McDonald V, McMeeken J, Nickson W, et al. Sports Physiotherapy: Applied Science and Practice. 1st ed. Melbourne: Churchill Livingstone, 1995.

6. Sherry MA, Best TM. A comparison of 2 rehabilitation programs in the treatment of acute hamstring strains. J Orthop Sports Phys Ther 2004;34:116;25.

7.  Bandy WD, Irion JM, Briggler M. The effect of static stretch and dynamic range of motion training on the flexibility of the hamstring muscles. J Orthop Sports Phys Ther. 1998;27:295–300

8. Pope, R. P., Herbert, R. D., Kirwan, J. D., & Graham, B. J. (2000) A randomized trial of pre-exercise stretching for prevention of lower-limb injury. Medicine and Science
in Sports and Exercise, 32, 271–277

9. Gesztesi, B. (1999). Stretching during exercise. Strength and Conditioning Journal, 21(6), 44.

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