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Hamstring Strains and the Askling L-Protocol

Hamstring strains are common in dynamic sports like sprinting, jumping and where quick eccentric contractions are common. Hamstring strains are most common injury in soccer. Rehabilitation from hamstring strains can be slow, and recovering from an initial injury does not mean an athlete will be free from further re-injury as recurrence of hamstring strains is quite common. It is therefore important to seek the best, evidence-based conservative management to achieve the best prognostic outcome. The Askling Lengthening-Protocol (Askling L-Protocol) is an example of a widely-used management protocol for hamstring strains that is supported in the current scientific literature.

Hamstring muscles

The hamstrings consist of three muscles : The biceps femoris, the semitendinosus and the semimembranosus.

The biceps femoris is comprised of long head and short head parts. Both parts attach to one of the bones that make up the shin, called the fibula bone, but only the long head originates at the the ischial tuberosity (i.e., the sit bone) of the pelvis. The short head originates at the back part of the thigh bone, called the linea Aspera of the femur bone.

The semitendinosus muscle also originates at the ischial tuberosity, but unlike the biceps femoris, it follows the inner side of the thigh and attaches to the upper inner surface of the tibia, the other bone that makes up the shin, called Pes Anserinus.

The semimembranosus is the most inner muscle of the three hamstring muscles. It also starts at the ischial tuberosity, but attaches to the tibia bone on the Condylus Medialis Tibiae. It is also connected to the popliteal oblique ligament at the back part of the knee, and the fascia cruris (i.e., the deep fascia, a type of connective tissue, of the leg).

Therefore, all three hamstring muscles begin at the same origin, but have different insertion points. As the hamstrings cross over two joints (i.e, the knee and hip), their action are different. The muscles function to move the joints and also stabilise the hip and knee. Generally, the hamstrings bend the knee and extend the hip. The hamstrings also rotate the knee, which is important for walking and running.

Hamstring strains anatomy

What is a hamstring strain?

Hamstring strains are caused by rapid contraction or overstretch of the hamstring muscle group, which causes high mechanical stress in the tissue. This results in varying degrees of rupture within the fibres of the musculotendinous unit (i.e., the area where the muscle forms tendon and attaches to bone).

Risk factors for hamstring strains

There are various proposed risk factors which may play a role in hamstring strains. Some include:

  • Increased age
  • Previous hamstring injury
  • Limited hamstring flexibility
  • Increased fatigue
  • Poor core stability
  • Strength imbalance

During activities like running and kicking, the hamstrings will lengthen as the hip flexes (i.e., bends forwards) and the knee extends (i.e, straightens), and this lengthening may go beyond the normal mechanical limits of the muscle, leading to microscopic damage to the muscles.

How do I know if I have had a hamstring strain?

Patients often report a sudden, sharp pain in the back part of the thigh usually during sporting activities. In severe strain, a “popping” or tearing impression can be described. Following the injury, muscle tightness and impaired range of movement at the knee and hip is also reported. Sometimes swelling and bruising are possible but they may be delayed for several days after the injury.

Rarely symptoms are numbness, tingling and leg weakness. These symptoms require a further investigation into sciatic nerve irritation. Large haematoma or scar tissue can be caused by complete tears and avulsion injuries (i.e., when the muscle tear pulls off bone fragments).

Hamstring strain grades

  1. Grade 1 (mild). Just a few fibres of the muscle are damaged or have ruptured. There rarely is compromise to the muscle power and endurance. Pain and sensitivity usually happen the day after the injury (depends from person to person). Patient normally complains of stiffness and some small swelling on the back side of the leg, but the knee functions properly and the patient is able to walk.
  2. Grade 2 (medium). Approximately half of the fibres are strained (torn). Symptoms are acute pain, swelling and a mild case of function loss. The patient’s walking pattern will be compromised with reduced hip flexion and knee extension.
  3. Grade 3 (severe). Ranging from more than half of the fibres ruptured to complete rupture of the muscle. Both the muscle belly and the tendon can suffer from this injury. It causes massive swelling and pain. The function of the hamstring muscle can’t be performed anymore and the muscle shows great weakness.

Rehabilitation of a hamstring strain

The primary goal of physical therapy for hamstring strains is to restore the function of the muscle group to the highest possible degree and/or to return the athlete to normal play and level of performance with minimal risk of reinjury. However, hamstring strains are a challenge for both athletes and clinicians, given their high incidence rate, slow healing and persistent symptoms. Furthermore, reinjury occurs approximately 30% of the time within the first year following return to sport, and often subsequent injuries are more severe than the first onset.

Several therapies, such as dry needling therapy, deep tissue massage and specific exercises have been used to rehabilitate hamstring strain; however, some have shown to be better than others. Recent systematic literature reviews on the effect of various therapies for the management of hamstring strains have concluded that the overall best intervention is specific hamstring muscle exercises.

Initial onset

The very first protocol to administer to any strain that has just occurred, is the P.O.L.I.C.E (Protect, Optimally Load, Ice, Compression, Elevation) protocol. This protocol is designed to initially manage swelling and symptoms and protect the injured tissue, thus reducing scar tissue formation.

Early stage

In the early stage of hamstring strain, isometric (muscle does not lengthen or shorten) strengthening and controlled, pain-free, low-intensity active movements are recommended.

Intermediate stage

In the intermediate phase, an increase in the intensity of exercises is prescribed, with neuromuscular training at higher amplitudes and the initiation of eccentric resistance training (where the muscle is lengthened under load). The positive effects of eccentric strengthening in hamstring injuries have been well established in the scientific literature. A study by Askling et al. (2013) found that eccentric was better than conventional exercises for hamstring strains, as it provided a faster return to sport and lower relapse rate. Restoring flexibility to promote better orientation of muscle fibres during healing has also shown to be important at this stage.

Final phase

In the final phase, it is recommended to increase eccentric training and high-speed sport-specific neuromuscular training, in preparation for the return to sport. A recent study found that functional training of lumbopelvic stabilisation during rehabilitation was associated with a higher return to sport rate and a lower strain recurrence rate.

The Askling L-Protocol

The Askling L-Protocol is an evidence-based protocol designed by researches in the paper by Askling et al. (2013) to effectively manage hamstring strains. The researchers concluded that rehabilitation protocols consisting of eccentric exercises are more effective in returning athletes to their sports following hamstring injury. Stretching and strengthening exercises selected should involve heavier loading in lengthened states.

The Askling L-Protocol is as follows:

  1. L1: The Extender. The athlete lies on their back and holds their thigh at approximately 90 degrees of flexion. The knee is slowly extended but stopped prior to pain. Three sets of twelve repetitions are performed twice every day.
  2. L2: The Diver. The athlete stands on the injured leg with the knee flexed to 10-20 degrees. Both arms are reached forward as the opposite leg is reached backwards. The lifted leg is held at 90 degrees of flexion and the goal is to lift that leg as high as possible. Thee sets of six repetitions are performed every other day at a slow tempo.
  3. L3: The Glider. The athlete starts with one hand holding a railing or support and 90% of the weight on the injured leg with 10-20 degrees of knee flexion. The uninjured leg is glided backwards, stopping before pain on the injured leg. The arms are then used to return the athlete to the starting position (avoiding contraction of hamstrings). Progress this exercise by increasing the range of motion and speed at which it is performed. Three sets of four repetitions are performed every third day.

Here below is a YouTube clip demonstrating the Askling L-Protocol.

Reference: Askling CM, Tengvar M, Thorstensson A. Acute hamstring injuries in Swedish elite football: a prospective randomised controlled clinical trial comparing two rehabilitation protocols. Br J Sports Med 2013;47(15):953-9.


Chris Knee

Chris is an experienced and qualified chiropractor, sports chiropractor, McKenzie Credentialed practitioner, nutritionist and Certified Strength and Conditioning Specialist (CSCS) and is finishing of his Doctor of Physiotherapy at Macquarie University.