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Hamstring muscle strains are frequent in different sports and are the single most common injury in professional football.1 Several studies have indicated that hamstring strains are frequent in track and field as well, especially among sprinters and jumpers.2 The re-injury rate is high,1 3 which in most cases probably indicates inadequate rehabilitation programme and/or a premature return to sport.4
Hamstring strains are a heterogeneous group, especially in terms of the different types of injuries, injury location and size.1 5,–,11 A majority of the strains are located in the proximal part of the hamstring muscles/tendons and the anatomy is complex, characterised by overlapping tendons and structural interrelations between the hamstrings muscles.12 13 Different sports put different demands on the hamstrings, for example, the elite sprinter probably needs full functional recovery after injury before competing again, but a football player can possibly play again without 100% restored function.14 Even psychological aspects on an individual level can affect the rehabilitation period.15 16 All these parameters make the prognosis after acute hamstring strains in terms of rehabilitation time and safe return to sport difficult to predict.
Type of hamstring strain – injury situation
There are at least two distinctly different types of acute hamstring strains, which are best distinguished by the different injury situations.6,–,8 11 17,–,19 The most common injury type occurs during high-speed running1 4 5 17 18 and the other occurs during movements leading to extensive lengthening of the hamstrings, such as, high kicking, sliding tackle and sagittal split.7 9 10 17,–,19 The high-speed running type is mainly located to the long head of biceps femoris and typically involves the proximal muscle-tendon junction.8 In contrast, the stretching-type is located close to the ischial tuberosity and typically involves tendon tissue of the semimembranosus.7
The strains occurring during high-speed running generally cause a more marked acute functional impairment, but typically require a shorter rehabilitation period than the stretching-type of hamstring strains.9 In a prospective randomised ongoing study (Askling et al, personal communication, 2011)dealing with acute hamstring strains in elite football (n=80), track and field (n=50) and other sports (n=40), we have noticed that different injury situations can result in different types of hamstring strains; for example, comparing hamstring strains typically sustained by sprinters versus dancers. The injury situation and the injury location can give important information about the injury prognosis. The injury location can be determined both by maximal pain upon palpation and by MRI during the first 2 weeks after injury occurrence. A general rule of thumb is, ‘the closer to the ischial tuberosity, the longer the rehabilitation period’.
The two types of hamstring strains require different approaches when rehabilitation is planned. In the case of high-speed running type of injuries, it is common for the athlete to experience a considerable improvement 4–6 days after the injury has happened, especially with respect to pain, strength and flexibility. This is, however, a potentially dangerous feeling because the healing process is still only in its initial stage and the risk for re-injury is evident since the injured tissue is less able to absorb energy. Slow jogging, without pain or limping can be allowed early in the rehabilitation process, whereas high-speed eccentric conditioning is an essential component of the later part of the rehabilitation.
For the stretching-type of injuries, it is important to inform the athlete that the rehabilitation period is likely to be prolonged, even though the initial symptoms are relatively mild in terms of pain and functional impairment. Too optimistic and unrealistic information will only reinforce the disappointment and frustration of the injured athlete. The athlete can undergo demanding rehabilitation training early on, as long as pain-provoking exercises are avoided. Passive stretching and heavy load exercises appear to provoke the stretching-type of injuries by increasing pain.
In the presently ongoing study (Askling et al, personal communication, 2011) on acute hamstring strains (170 elite athletes included), where the aim is to compare two different rehabilitation protocols, that is, conventional exercises versus lengthening exercises, with respect to time loss and return to sports, we have observed that the protocol that included lengthening exercises shortens the rehabilitation period significantly in both types of hamstring injuries. Before the athletes are allowed to return to full training and competition they should perform a hamstring test without any remaining symptoms or signs of injury.15 So far we have only noticed one re-injury in athletes included in the study.
Taken together, hamstring injuries are more common than previously anticipated and it has become increasingly known how difficult they are to treat. Recurrences are common, but can probably be avoided to a large degree, provided sound knowledge about the injury type, injury location and size. Strict adherence to rehabilitation, especially in terms of time and loading is of greatest importance.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.