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INJURY PREVENTION HAMSTRING INJURY
Of these, 67 players suffered a clinically diagnosed lower limb injury, of which 31 were hamstring injuries. Subjects with hamstring injuries showed a significantly lower mean flexibility of their hamstrings (P=0.02). However, despite increasing interrater reliability by using the same physiotherapist to perform the initial flexibility measurements and good validity, shown when using the universal goniometer, it was not indicated how they ensured no lumbar spine movement during the straight leg-raise (SLR) to test the length of the hamstring (15). The other important factor is that whether the SLR is a direct measure of hamstring flexibility or length is questionable.
Study 6 Lew and Puentedura showed in their study that cervical spine movement significantly affected the SLR test, therefore indicating that the test is also a test of the neural system’s mobility and not purely the hamstrings (16). The study’s validity may be questioned as not all participants could be classed as equal before the study; the exclusion criterion was any soft tissue injury in the previous 2 years. Subjects may have had numerous injuries before this, possibly introducing other factors that may have caused injury rather than their lack of flexibility. The way in which the injury occurred, and specific training that occurred during the season at each individual club, were not documented or controlled and therefore affected the overall validity of the results, as not all subjects were treated equally during the study.
Study 7 Rolls and George aimed to determine the relationship between hamstring injury and hamstring length in a prospective study (17). The hamstring length of 111 football players aged 9–19 years, with no lower limb injury, was assessed using the modified sit and reach test (mSar) (18), SLR, active knee extension (AKE) (19), passive knee extension (PKE) and seated knee extension (SKE) (20) tests. All measurements were taken by the same physiotherapist in the same order. After the initial screening, any subject complaining of posterior thigh pain was assessed by the club’s medical practitioner, who decided
whether the hamstring muscles were injured and to what grade according to guidelines set by Kujala et al. (21). Of the 93 subjects who had remained at the club at the end of the season, 20 hamstring injuries were reported, 39% in the players aged 17–19 years. There were no statistically significant differences (P>0.01) between the injured and non-injured athletes’ hamstring flexibility, but the authors did note a general pattern for reduced hamstring length in the injured group. It was also noted that there was an increased injury rate and lower flexibility among the older players. Again, this was only a trend and not scientifically significant, and it was apparent only in the AKE and PKE tests. More significant results could have been obtained with a more robust randomisation of a greater sample size to eliminate bias. The higher injury rate may have been due to increased exposure to training and game time, but information regarding this area was not collated. Despite the data not being clinically significant, the trend for lower hamstring flexibility in injured subjects may not be attributable solely to variability in measurement alone. It may also be due to the large interindividual variability in subjects’ growth rate, training and pre-habilitation work, and the reliance on the subject to seek help regarding pain. Again, this could be clarified with a larger sample size in varying age groups to increase the validity and reliability of the study.
CONCLUSION Evidence shows that the incidence of hamstring injury can be reduced with preventative training regimes. The rationale for stretching before exercise is to improve muscle compliance and decrease stiffness in order to limit the amount of force generated within the muscle at a given stretch. There is still a lack of RCTs reflecting various types of stretching and the length of time for stretching for specific sporting activities. This lack of good-quality evidence leads to conflicting information. Whatman and colleagues found a significant increase in knee range following hamstring stretching lasting up to 20 minutes (7), but it is unknown whether this stretching has a prolonged effect to reduce hamstring injury. This concurs with Pope et al., who found a small but non-significant reduction in lower limb injury but were unable to determine the
effect on hamstring stretching alone (8). There is conflicting evidence regarding increasing flexibility outside the pre-exercise time. Evidence suggests that increasing hamstring flexibility in the long term will increase the ability of the muscle to absorb energy and therefore reduce the injury risk (22). This concurs with Witvrouw et al., who found that subjects with decreased hamstring flexibility incurred hamstring injuries (14). However, an unreliable measure of hamstring flexibility and lack of acknowledgement regarding other intrinsic and extrinsic risk factors allow results to be questioned. Rolls and George, however, found no clinical significant differences between hamstring flexibility and injury rates, although they did not control other risk factors and relied on the subjects themselves to report hamstring injury (17). It would appear that further evidence is required to fully understand the role of increasing hamstring flexibility outside the pre- exercise time to reduce hamstring injury. Evidence suggests that hamstring
injury occurs mainly during the eccentric phase of running, and strengthening the hamstring muscles eccentrically can reduce hamstring injury. The notion that the greater the range through which the muscle is weak, the greater the risk of injury (11), is backed up by Clark et al. (10) and Arnason et al. (13). Clark and colleagues showed a clinically significant decrease in knee joint angle at which peak torque occurs following eccentric training (10), and Arnason and colleagues found a significant decrease in hamstring injuries following eccentric training (13). However, repeated eccentric contractions have been shown to induce DOMS, and this should be considered when incorporating eccentric training into training programmes. The evidence suggests that
incorporating eccentric strength training may reduce the incidence of hamstring injury, but more research is required on how to achieve this in order to ensure that it does not induce injury. There is conflicting evidence regarding the need to increase overall flexibility outside pre-exercise time. There appears to be no evidence regarding a detriment to increased hamstring length, but the evidence suggests that pre-exercise
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