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INJURY PREVENTION HAMSTRING INJURY
as it is not stated whether the same physiotherapist performed the stretches.
minute intervals for 20 minutes. The protocol was repeated with participants performing 90 seconds of mid- range isotonic knee flexion/extension exercises between tests. Results showed an increase in peak angle following stretching, and stretching with exercise, for every post-stretch measurement, greater than the control conditions. The greatest clinical and statistically significant change was seen immediately post-stretch: a 4.9° increase in knee range of motion (P=0.001). To be clinically applicable in the sporting world, results need to be obtained for longer in order to show any benefits in sports where competition lasts for more than 20 minutes. This trial’s small sample size of nine participants and lack of clarity regarding the participants having any previous hamstring injuries impacts on the validity of the results. The inter- tester reliability is also questioned,
Study 2 A study by Pope and colleagues showed no significant reduction in rate of injury with pre-exercise stretching (8). In a randomised controlled trial (RCT), 1,538 male army recruits were assigned randomly to a stretch or control group by staff blinded to the study. Both groups performed active warm-ups before physical training, with the stretch group performing one 20-second stretch under supervision for each of the six main leg muscle groups during each warm-up. After 12 weeks of training, 333 lower limb injuries were recorded, of which 214 of were soft tissue injuries. A total of 158 injuries were in the stretch group and 175 in the control group. This means that, although there was a small reduction in risk of soft tissue injury, it was not statistically significant (P=0.67). This RCT had a high participant rate and can be generalised to the sport- ing population, as the stretches used reflect those commonly used, in time and type, within sport. However, the study lacked a true control group that performed no warm-up exercises, and the collection of injury data relied upon recruits reporting injuries, which were referred on to researchers only if they were unable to resume full duties within 3 days. This study was based on generalised lower limb stretching, and therefore it is difficult to determine the use of hamstring stretching solely in the reduction of hamstring injury.
The hamstring muscles work
in synergy with the prime movers, quadriceps, acting to decelerate the lower limb during running (9). Epidemiological evidence shows that hamstring injury often occurs during the eccentric contraction of the hamstring muscle (10), and due to the biarticular nature of the muscle group they are subjected to large length changes (9). Delayed-onset muscle soreness (DOMS) after exercise is an indicator of fibre damage and can be caused by repeated eccentric muscle contraction (9). These microscopic areas of damage may cause the muscle to have an area of weakness, with the possibility of a larger soft tissue injury occurring later (10). Pull and Ranson also indicated that the position of knee extension at which peak hamstring torque occurs is potentially a risk factor for hamstring injury (11). Training to increase the knee extension angle at which peak torque occurs may result in decreased eccentric loading and susceptibility of hamstring injury, as it is stronger throughout a greater range (10).
Study 3 Clark and colleagues (10) investigated whether eccentric hamstring training, via the Nordic hamstring exercise (12), could adapt the length–tension relationship in order to reduce hamstring injury (Figs. 1–3). Nine amateur Australian football players, with no history of hamstring injury and who did not participate in regular lower limb strength training, underwent pre- and post-training isokinetic dynamometer
Figure 2: Midway through the Nordic hamstring exercise
Figure 3: Completing the Nordic hamstring
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