# Assessment of Limb Imbalance in Professional Soccer Players
## 4 Discussion
### Tests Measuring Power with Flexibility  
Jumps occur frequently during match play, and asymmetry is a natural by-product of competing in a single sport over time [56]. In this respect, the continuous and recurrent execution over time of a gesture that involves a maximum expression of force in the shortest possible time can cause the limb imbalance generated to be of greater magnitude [57]. Therefore, it would be prudent to minimize limb differences in dynamic balance and optimize ankle range of motion for better jumping and change of direction performance [16]. A variety of jump tests have been shown to be valid and reliable measures for quantifying limb asymmetry [58]. Additionally, significant differences in jump height have been observed between limbs, with a limb imbalance of around 10% between the injured and uninjured limbs [18].  
To our knowledge, there are no studies that have worked on power in isolation. However, studies were found that analyzed power with flexibility [35; 59]. The power-flexibility relationship is of vital importance for efficient ball striking [60]. On the one hand, [PERSON] et al. [35] used the Landing Error Scoring System (LESS) to assess both unilateral differences between agonist and antagonist muscle groups and limb imbalance during the execution of a high jump [35], finding that worse landing mechanics were obtained (\(p<0.001\)) for soccer players when jumping higher. In turn, they used the FMS test to assess flexibility, concluding that flexibility in the FMS test could limit landing mechanics. However, in the studies by [PERSON] et al. [40], who also analyzed jumping power alongside flexibility, they found that the assessment of unilateral and limb imbalance obtained through the FMS test showed a negative relationship with respect to jumping ability. Therefore, [40] showed an inverse relationship between the score obtained in the FMS tests and the limb imbalance produced in the jumping tests (\(p<0.01\)). This could be due to the fact that the soccer players developed an improved stretch capacity in their musculature, producing a more developed flexibility in their lower limbs, which would help them to improve their jumping mechanics and, therefore, provide them with a greater capacity to reduce the limb imbalance observed in these jumps. There is currently no scientific evidence for this; thus, more research should be carried out on professional soccer players to see if this hypothesis holds true.  
From another perspective, [PERSON] et al. [50] analyzed the relationship of power to other qualities, such as flexibility and strength. Power was assessed through countermovement jumping (CM) with one and both legs. Unilateral imbalance was assessed through strength testing, while limb imbalance was measured through knee, hip, and hamstring ROM. In this regard, differences in strength tests (\(p<0.05\)) were observed between limbs, highlighting the presence of asymmetry in strength among soccer players [50]. It is important to note that such differences in strength may contribute to limb imbalances in soccer players [61; 62]. In turn, [PERSON] et al. [39] also concluded that jumping tests showed no relationship to limb imbalance in flexibility and strength tests. Therefore, more research is needed to relate the asymmetry of flexibility and strength to jumping tests. On the other hand, there were differences between the jumping and strength variables (\(p<0.05\)); it was found that the group with very high asymmetry in the jumping tests had lower scores in the isokinetic strength test. This may be because soccer players with lower knee extensor and flexor strength would have been more likely to show high limb imbalance in jumping [63].  
In summary, better scores on the FMS tests seem to produce less asymmetry in the jumping tests. On the other hand, it was also determined that limb imbalance in flexibility and strength did not affect jumping performance, requiring future research to corroborate that greater asymmetry does not prevent reduced jumping performance.