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Hamstring Injury Prevention


Hamstring injury prevention is on the mind of any athlete that participates in high intensity or high speed sports. Those involved in kicking, sprinting and jumping sports are at particularly high risk. There is plenty of evidence in the literature that indicates a relationship between recurring hamstring injury and flexibility, strength, fatigue and warm-up. Physical therapists will design exercise programs to specifically enhance flexibility of the  hamstrings so as to prevent injury.

What are the hamstrings
How do hamstrings work
Hamstring Injury Prevention - why do they recur?
How to Minimize the Risk of Recurrence
Hamstring warm up
Hamstring stretches
Hamstring Strengthening
The Nordic Hamstring Exercise

assisted hamstring stretch

What are the Hamstrings

Here is a quick review of the anatomy. The hamstrings are comprised of the semimembranosus, semitendinosis, and biceps femoris muscles and comprised mostly of type II muscle fibres. Hence, they are designed for short strong bursts of activity, but tend to fatigue quickly. The biceps is composed of two heads - the long head crosses the hip joint, the short head does not. Both heads cross over the knee joint and insert into the fibular head and lateral condyle of the tibia and deep fascia of the leg. Innervation is from two separate nerves; the short head is innervated by the peroneal part of the sciatic nerve; the long head by the tibial portion.

The medial hamstrings are comprised of the semimembranosus and semitendinosis muscles. Both originate on the pelvis, cross the hip joint and insert into medial, posterior aspect of the tibia. Both the semimembranosus and semitendinosis are innervated by the sciatic nerve's tibial portion.

How do hamstrings work

Simplistically, the hamstrings work to extend the hip and flex the knee. To fully appreciate the role of the hamstring muscles in running we need only look at walking. While walking we spend 60% of the time with our foot in contact with the ground, 40% of the time swinging it forward. While running, there is a period where neither foot is in contact with the ground. The faster we run, the more time each leg is in this swing phase not in contact with the ground. When contact does occur, the hamstrings (as well as other muscles) must contract quickly and absorb forces over a shorter time.

Hamstrings will act eccentrically just before the foot strikes the ground and continue to work to begin knee flexion and hip extension. It is often during this transitory period when this eccentric activity is occurring and transitioning into a concentric contraction that injury takes place.

Hamstring injury prevention - why do they recur?

Studies done with football players show that 12 percent of hamstring injuries amongst football players will recur.(1)  This is because the hamstring muscle heals with scar tissue. Without the proper physical therapy this scar can be left weak and prone to tearing again with the loading incurred during a sporting event. Scar  tissue is not as elastic as the rest of the muscle so is prone to strain. Although the greatest  incidence of re-injury is within a week of returning to sports, the risk remains even several weeks after pain is gone and the individual has returned to sports. Hamstring injury prevention needs to remain a concern for some time after an injury.

How to Minimize the Risk of Recurrence

In order to prevent hamstring injuries it is advisable to minimize the following risk factors in a training program:
  • hamstring weakness
  • reduced flexibility (tight hamstrings)  Anyone with flexibility deficits needs to be put on an appropriate stretching program. This type of stretching should be done daily.
  • poor core strength
  • improper warm up
  • fatigue
  • low quadriceps/hamstring strength ratio
  • poor body mechanics while running

Part of a hamstring injury prevention program is adequate warm up

Five to 10 minutes of bicycling allows for increases in hamstring temperature without creating micro-trauma. Intensity should be light to moderate to break a sweat.  An intense eccentric workout should for the basis of a hamstring injury prevention program. The muscles must be adequately warmed up prior to these types of exercises in order to prevent a future hamstring injury. Studies with rabbits show that warmed up muscles require more force before failure occurs and the the warmed up muscle will stretch further before failure.

An active warm up including sport specific movements cause an increase in muscle temperature and metabolism. This increases elasticity and therefore dynamic flexibility. Active movements that occur during the particular sport need to be emphasized.

Hamstring stretches

Hamstring tightness may be the single most important factor seen amongst athletes suffering recurring hamstring injuries.

Stretching prior to exercises and sports should be controlled and dynamic and geared toward the movements that occur during the particular sport.
See dynamic stretching for more information on warm up stretches.

Static stretches are more appropriately performed during a cool down. In any sport that includes a lot of eccentric muscle activity,  a tightening up occurs after play. Static stretching while the muscles are warm will garner maximum benefit.

Strengthening for hamstring injury prevention

Several studies suggest that poor hamstring strength may be a risk factor for hamstring strains.(2,3) Part of a good hamstring injury prevention program requires resistance exercises. As the muscle is strengthened, as are the connective tissues.

Resistance exercises are used normally to increase musculature, size and strength of a muscle or muscle group. Hamstring strengthening should increase core stability, alter the position of peak torque to a straighter knee, and help to improve flexibility. In the context of hamstring injury prevention, eccentric training has been shown to increase connective tissue strength. So, any hamstring strengthening program must include both concentric strengthening and eccentric strengthening exercises.

The Nordic Hamstring Exercise

This method of strengthening the hamstrings uses concentric as well as eccentric contractions which has been shown to improve vertical jump, improve strength, increase flexibility, and alter the position of peak torque. (4,5) This is a very intense exercise for the hamstrings so be sure you are well warmed up prior to attempting it. If you have a history of hamstring injuries you would be wise to consult your physical therapist prior to doing this hamstring exercise.

WARNING:  THIS EXERCISE CAN CAUSE REINJURY TO YOUR HAMSTRINGS IF YOU HAVE PREVIOUSLY STRAINED THEM. If you have a history of hamstring injuries you would be wise to consult your physical therapist prior to doing this hamstring exercise.

Studies have shown that this exercise reduces the risk of hamstring injuries.
To perform this exercise, follow the instructions:

  1. Start in a kneeling position with your hips straight and chest up.
  2. Use a heavy barbell or have your training buddy hold your heels to keep your feet in contact with the floor throughout the exercise.
  3. Slowly lower your body toward the floor using your hamstrings to control your descent. Perform this movement as slowly as possible.
  4. Once at the bottom, gently push yourself up a couple of inches and then use your hamstrings to pull yourself back up to the vertical.
Due to the intensity of this exercise it is not advisable that it or any other heavy eccentric exercise be performed year round. The gains from eccentric training last long after the last training session, so one needs to be careful not to over train.

The advantage of this exercise is that the lower you get to the ground the greater the gravitational pull or torque on the knees, hence strengthening occurs in a way to create a greater torque at straighter knee angles.

This exercise only increases eccentric strength. To round out a good hamstring injury prevention program you must also include concentric strengthening such as hamstring curls and dead lifts. Again, consult your physical therapist for the appropriate exercises.

During a cool down it is best to include some aggressive hamstring static and pnf stretching for hamstring injury prevention.

Core strength is best addressed with the exercise ball for exercise ball exercises.
References
1.  Bennell K, Crossley K. Musculoskeletal injuries in track and field: incidence, distribution and risk factors. J Sci Med Sport 1996;28:69-75.

2.  Yamamoto T. Relationship between hamstring strains and leg muscle strength. A follow-up study of collegiate track and field athletes. J Sports Med Phys Fitness 1993: 33:
194–199.

3.  Orchard J, Marsden J, Lord S, Garlick D. Preseason hamstring muscle weakness associated with hamstring muscle injury in Australian footballers. Am J Sports Med 1997: 25: 81–85.

4. Clark RA, Bryant AL, Culgan J, Hartley B. The effects of eccentric hamstring strength training on dynamic jumping performance and  isokinetic strength parameters: a pilot study on the implications for the prevention of hamstring injuries. Phys Ther Sport 2005;6:67-73.

5. Nelson RT, Bandy WD. Eccentric training and static stretching improve hamstring flexibility of high school males. Hamstring injury prevention J Athletic Train 2004;39: 254-8.

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