The hamstring muscle group consists of 3 main muscles : biceps femoris, semimembranosus and semitendinosus.
Hamstring muscle injuries are a common injury in sports that involve high-speed running and kicking, especially football, squash, hockey and rugby.
Biomechanics of Hamstring Injury
The majority of hamstring muscle injuries occur in the biceps femoris muscle, mainly at the muscle-tendon junction. They are usually a non-contact injury and mostly occur during sprinting. Recent studies have demonstrated that during sprinting, the point of failure is most likely to occur during the terminal swing phase just prior to foot strike. It is at this point when the hamstrings are working eccentrically that they are maximally activated and are approaching peak length.
Factors that Predispose to Hamstring Strain
Several studies have shown that increasing age is a risk factor for hamstring muscle injury. It has been shown that athletes over the age of 23 years old were four times as likely to sustain a hamstring strain than those younger than 23.
Previous hamstring injury is a major risk factor, which may be associated with reduced strength.
There is an increased incidence of hamstring injury in those of black ethnic origin.
Studies have shown that reduced hamstring flexibility leads to an increased risk of hamstring injury and the implementation of stretching exercises may help prevent its occurrence.
Low hamstring strength has been shown in most studies to be a significant predictor of hamstring muscle strain injury.
Increased neural tension can lead to hamstring pain. The presence of myofascial trigger points in the gluteal and hamstring muscles appear to be associated with decreased flexibility and possible increased motor firing of the muscle.
Neuromuscular control of the lumbo-pelvic region, including anterior and posterior pelvic tilt, may be needed to create optimal function of the hamstrings in sprinting and high-speed skilled movement patterns.
Age-related lumbar spinal degeneration leading to L5 and S1 nerve impingement may lead to hamstring and calf muscle fibre denervation, which then leads to decreased muscle strength. A bilateral anterior pelvic tilt has also been associated with weakness of the transversus abdominis muscle, which may make the hamstrings functionally tighter.
A physiological warm-up consisting of isometric contractions increases the amount of force and length of stretch that the muscle can absorb prior to tearing. There appears to be clinical evidence that muscle strain injuries, in genera, are more likely to occur without adequate warm-up.
Fatigued muscles are able to absorb less energy. Hamstring injuries are more common at the end of matches and training sessions in football and have a higher incidence in the fourth quarter of Rugby Union. Fatigue may induce physiological changesa within the muscle, as well as altered coordination, technique or concentration, predisposing the player to injury. It has been shown that when footballers become fatigued during sprinting there is an earlier activation of the biceps femoris and semitendinosus muscles.
Inadequate pre-season training resulting in low fitness levels may contribute to an increased hamstring injury rate.
Too much emphasis on aerobic training instead of more high-intensity running acceleration drills has been suggested as a causative factor. Abrupt increases in training volume and intensity may also contribute to injury risk.
This may lead to deficits in strength and/or flexibility.
Prevention of Hamstring Muscle Injuries
A warm-up stretching programme has been found to reduce the number of hamstring injuries.
Pre-season hamstring strengthening using an open chain weight machine and specifically eccentric training has reduced the number of injuries.
A number of multi-factorial programmes appear to have been effective in reducing the number of hamstring injuries. Examples include : increasing the amount of anaerobic interval training rather than aerobic training, stretching while the muscle is fatigued, closed chain rather than open chain leg weights, sports-specific training drills, plyometric exercises and regular warm ups and cool downs.
The main aim of examination is to differentiate between hamstring tear, neuromyofascial referred pain and pain from lumbar spine structures.
Hamstring Muscle Tear
Sudden onset, moderately severe pain, difficulty walking and running, painful, reduced stretch, reduced strength against resistance, local bruising, marked tenderness, abnormal ultrasound and MRI.
Referred Hamstring Pain
Sudden onset or gradual feeling of tightness, less severe, although cramping or twinging, able to walk or jog pain-free, minimal reduction in stretch, no localised bruising or tenderness, Slump test positive, gluteal trigger points evident, lumbar spine signs, normal ultrasound and MRI.
Ultrasound and MRI have both been found to be effective in depicting hamstring injuries. MRI has the capability of being a strong predictor of the amount of time needed until an athlete can return to competition.
Management of Hamstring Strain
The RICE protocol should be commenced. For the first 48 hours, pain-free active knee extension exercises while sitting following 10-15 minutes of ice application.
The role of anti-inflammatory medication (NSAID’s) in the treatment of acute muscle injuries, such as the hamstring is controversial. The most common recommendation in the literature is short-term use (3-7 days), starting immediately after injury. The intended aim of using NSAID’s is to keep the inflammatory process under control and to provide analgesia. However, the normal healing process could be blunted as a result and the response delayed.
There is a case to delay treatment with NSAID’s until 2-4 days after injury because the drugs interfere with the process involved in repair and remodelling of regenerating muscles. It therefore may make more sense to use simple analgesics (paracetamol) in the first 48 hours for pain relief. However, a short course of NSAID’s may be helpful if there is an excessive inflammatory response within the muscle following injury.
In the acute phase following injury, pain-free range of motion should be achieved as soon as possible. If there is long-term loss of range of motion, then specific stretching should be undertaken to focus on the affected area.
Soft Tissue Therapy
At an appropriate time, depending on the severity of the injury, soft tissue techniques can be used in the treatment of hamstring strains. These include, massage, sustained myofascial tension release and digital ischemic pressure techniques.
The presence of a degree of hypomobility in any segment of the lumbar spine, found on examination, should be treated with mobilisation or manipulation techniques. If increased neural tension is found at examination, neural stretches should be included in the treatment regimen.
Strengthening is an essential component of prevention and rehabilitation of hamstring injuries. In view of the probable mechanism of hamstring injury, it is likely that eccentric strength is particularly important in terms of recovery and further injury prevention.
Muscle strengthening is mode-specific. In other words, concentric muscle exercises lead to increases in concentric strength and eccentric muscle exercises lead to increases in eccentric strength, with little or no crossover.
Therefore, to increase eccentric hamstring muscle strength, it is necessary to perform eccentric muscle training. The use of the Nordic eccentric exercise and the ‘drop and catch’ exercise have been shown to be more effective than traditional concentric strengthening in developing eccentric hamstring strength.
Eccentric muscle training results in muscle damage and delayed onset muscle soreness (DOMS) in those unaccustomed to it. Therefore, any eccentric strengthening programme should allow adequate time for recovery, especially in the first few weeks.
Strengthening exercises for the hamstring group should therefore consist of a mixture of concentric and eccentric exercises.
Muscles that assist the hamstrings
Strengthening of the hamstring muscle group should always include specific work to ensure adequate gluteal and adductor magnus conditioning as these assist in sprinting activities.
Neuromuscular control of the lumbo-pelvic region, including anterior and posterior pelvic tilt, may be needed to create optimal function of the hamstrings in sprinting and high-speed skilled movement.
A rehabilitation programme consisting of progressive agility and stabilisation exercises has been shown to be more effective in promoting return to sport and in preventing injury recurrence in athletes who have sustained an acute hamstring strain than has a more traditional stretching and strengthening exercise programme.
Progressive Running Programme
Early commencement of a progressive running programme is an important part of rehabilitation following a hamstring muscle injury.
The basic principles are listed below :
1. Running programme start 48 hours after injury.
2. 20 minute jog preceded by 10 minutes of gentle hamstring stretching
3. Patient encouraged to increase stride length gradually over the session as pain or aching allows.
4. Interval running over 100 metres with acceleration, maintenance and deceleration phases.
5. If there is even the slightest increase in pulling sensation through the hamstring, then the session must immediately cease. The patient should apply ice and the programme can be attempted again as early as 24 hours.
6. Finish with 10 minutes of gentle hamstring stretching and then apply ice to the injured area for 10 minutes.
Criteria for Return to Sport
The length of time is proportional to the severity of the injury. Generally, an athlete with a mild hamstring strain may be able to return to sport in 14-21 days if optimally treated. Rather than a specific time frame it is preferable to have a definite criteria for return to sport.
1. Completion of progressive running programme
2. Full range of movement (equal to uninjured leg)
3. Full strength (equal or almost equal to uninjured leg)
4. Pain-free maximal contraction
5. Sprinting from a standing start
6. Abrupt changes of pace and direction during running
7. Successful completion of a full week of maximal training
8. It is important to continue the strengthening programme for a few weeks after return to sport.
Other Causes of Hamstring Pain
The possibility of referred pain should always be considered in the athlete presenting with posterior thigh pain. Hamstring pain may be referred from the lumbar spine, sacro-iliac joint or the soft tissues, such as gluteus maximus, gluteus medius and piriformis muscles. Often there is a history of previous or current low back pain. A positive slump test is strongly suggestive of a referred component to the patients pain.
Trigger points are common sources of referred pain to both the buttock and hamstring areas. The most common trigger points that refer pain to the mid-hamstring are the gluteus minimus, gluteus medius and piriformis muscles.
The patient will often complain of a felling of “tightness”, “cramping”, “twinging”, or a feeling that the hamstring is “about to tear”. On examination, there may be some localised tenderness in the hamstring although it is usually not focal and there is restriction in hamstring and gluteal stretch. Firm palpation of the gluteal muscles will detect tight bands that contain active trigger points, which when firmly palpated are extremely tender, refer pain into the hamstring and elicit a ‘twitch response’.
Treatment involves deactivating the trigger point either with ischemic pressure using the elbow or dry needling. Folowing the local treatment, the tight muscle groups, gluteals and hamstrings, should be stretched.
The lumbar spine is a source of pain referral to the posterior thigh. Pain may be referred from the disc, joints, muscles and ligaments. Nerve root compression may also be a cause of hamstring pain. Pain may be referred from the disc, joints, muscles or ligaments. Nerve root compression may also be a cause of hamstring pain and can be typically associated with numbness or weakness alongside the symptoms of pain. These nerves arise from the lumbo-sacral plexus, specifically from the roots of L5, S1 and S2.
Upper Hamstring Tendinopathy
Tendinopathy of the hamstring may occur at the origin or the insertion of the hamstring muscle group. Tenderness is easily elicited over the tendon with associated thickening. The condition is often associated with repetitive sprinting. A hamstring strengthening programme should be commenced alongside soft tissue treatment techniques or shockwave therapy.
It is often difficult to distinguish between hamstring tendinopathy and ischial bursitis. Both conditions have an inflammatory pain pattern at the origin of the hamstring muscle. An inflamed bursa is not easily palpated , however, patients tend to complain of pain when sitting on hard surfaces where the ischium is under pressure. For treatment, cortisone injections, under x-ray control appear to be the most beneficial.
Lower Hamstring Tendinopathy
This is often the result of large volumes of resisted knee flexion exercises. Management consists of anti-inflammatory agents, taping techniques and appropriate strengthening exercises.
Avulsion of the Hamstring from the Ischial Tuberosity
This is seen in 2 groups of patients : adolescents who instead of sustaining a hamstring muscle tear, tear their hamstring from its bony attachment at the ischium, and older people, often with a history of chronic tendinopathy.
Young sports people in the 14-18 year age range are prone to avulsions from the ischial aphophysis. Any young adult presenting with an incident of acute severe hamstring pain should be treated as if with an avulsion until proven otherwise. Plain x-ray or bone scan may be used to identify the avulsion. A separation of greater than 2cm requires surgical fixation. Separations of less than 2cm are usually managed conservatively, requiring 8-12 weeks rest and a strict rehabilitation programme aimed at regaining range of movement and strengthening.