Some risk factors, like ethnic origin, sex, age and previous hamstring injury are non-modifiable. A meta-analysis by Freckleton and Pizzari (2013) investigate a variable range of non-modifiable factors, and found the age (increasing with age), and previous history of hamstring injury to be most significantly associated with RHI. The mean age of the injured soccer players differs ranged from 23 to 26 years old. The age profile could be related to the level of play or the likehood of the player with a hamstring injury was older than uninjured players. In addition, Freckleton et al (2014) demonstrated a significant deficit in preseason single leg hamstring bridge performance on the soccer players who subsequently sustained a hamstring injury, supported the evidence of the history of previous hamstring injury and increasing age as significant risk factors for RHI. Nevertheless, it is unclear to concretely conclude whether the reinjury is due to slow recovery process, inadequate post injury rehabilitation, or premature return to play. It has been observed in several studies (Fyfe et al, 2013; Silder et al, 2013) following hamstring injury that minimal exposure to eccentric load could potentially cause several maladaptations, including chronic weakness and imbalance of lower limb muscle. Therefore, it is suggested the non-modifiable …show more content…
Various modifiable risk factors have been reported by different authors, with varying levels of evidence and often conflicting, including athlete weight, playing position, quadriceps peak torque, quadriceps flexibility, hip flexor flexibility, lower limb strength asymmetry and hamstring/quadriceps to hamstring ratio (Beijsterveldt, 2013; Chalmers, 2013; Freckleton, 2013). Of these modifiable risk factors, the quadriceps peak torque has shown as strong association with the future incidence of RHI (Tol et al, 2014). Even so, it is difficult to evaluate the quadriceps peak torque in a real soccer environment because: I) it does not reflect the biomechanical aspect where the hamstring injury is most predisposed to strain in sprinting and II) most soccer clubs do not have access to isokinetic testing equipment (Brughelli et al, 2011). Next, other modifiable factors such as hip flexors flexibility and hamstring to opposite hamstring strength symmetry (Schache, 2011), showed some evidence but inadequate the study power or could not be analyzed (mostly due to the rigorous methodology warranted in such evaluation) in a meta-analysis to strongly verify their relationship to RHI. Overall, a common barrier in interpreting the clinical significance of these