# Assessment of Limb Imbalance in Professional Soccer Players
## 4 Discussion
### Tests Measuring Flexibility  
The high-intensity demands of the movements required in soccer could lead to overloading joints and muscles, generating sport-specific adaptations that would cause deficiencies in the normal range of motion of muscles such as the quadriceps or hamstrings during soccer activities and that, therefore, may produce a notable risk of injury [48]. Poor flexibility is a risk factor for hamstring strain injury and is still considered a major risk factor for injury by professionals working in premier league soccer clubs [49]. Therefore, soccer teams include hamstring flexibility assessments in preseason testing to identify players who are more susceptible to hamstring strain [50]. In the present study, four papers were identified that investigated asymmetry using flexibility tests [27; 36; 37; 42]. [PERSON] and [PERSON] [37] found significant differences (\(p<0.001\)) in hip abduction and internal rotation ROM, with asymmetry observed between limbs in soccer players. Specifically, these parameters showed increased hip abduction ROM and decreased hip internal rotation ROM in one limb compared to the contralateral limb. It can be concluded that the assessment of asymmetry in soccer players is more effective when measuring hip ROM than measuring the knee and ankle joints. This may be because the hip is one of the important lower body joints used during instep strikes in soccer [51]. In contrast, [PERSON] et al. [36] assessed asymmetry by measuring the ROM of the ankle, knee, and hip joints. In this study [36], no significant changes in asymmetry were found. This may be because they only evaluated soccer players, which tends to homogenize decompensations located in the lower limbs. Furthermore, in this study [36], they did not use a control group; hence, the data were compared between the soccer players analyzed. Future research should investigate whether this imbalance does not occur due to soccer practice. It would therefore be advisable to conduct a study in which we observe whether this imbalance occurs in other kick dominant running team sports such as Australian Football, Gaelic Football and Rugby. Another study [27] assessed hamstring flexibility by measuring ROM using the ASLR and PSLR tests, specifically examining right/left asymmetry in hamstring flexibility. They compared the results from both tests and concluded that the PSLR was a more suitable measure for detecting hamstring flexibility asymmetry than the ASLR. The ASLR test does not accurately assess hamstring flexibility in soccer players due to the involvement of other muscle groups [52]. Therefore, the ASLR test is a more complex task than the PSLR test, and poor scores do not necessarily indicate only a hamstring flexibility deficit [27]. Consequently, the PSLR test seems to be a test that analyzes hamstring flexibility in a more individualized way. Therefore, the use of the PSLR is recommended instead of the ASLR, although its application requires more time; hence, it is not as practical in this regard. Finally, [PERSON] et al. [42] analyzed flexibility using the FMS test, a tool to assess functional mobility and postural stability in different non-locomotion settings [53]. In this case, the FMS test was found to have adequate sensitivity to assess the functional consequence (on flexibility) of a previously sustained lower limb injury. During the examination period, injured players had lower FMS scores than non-injured ones. When analyzing the FMS scores and injuries on the basis of additional aspects, it was found that the players who did not have injuries typically achieved better FMS scores in their average results than their injured peers, though this difference was not significant in terms of the variables [42].