## 4 Discussion
This obviously depends on the global body's potential to provide correct limb alignment and efficient force dissipation. We considered this test as a necessary supplement to the triple-hop test. The prone bridge test was among the supplementary tests we selected to structure a more holistic functional profile of the players. It assessed the endurance of the frontal trunk and lower limb muscles while stabilizing the trunk in a high-leverage position. Core stability has drawn attention to its connection to functional performance and injury prevention [25; 26; 41]. A stable core provides the basis for the effective load transmission between body segments and especially during hopping or high-velocity cutting, it keeps torques produced by the torso to safe limits. Failing to control the trunk during dynamic high-energy maneuvers, often occurring in football, would let the upper body sway excessively and put the knee under ACL injury predisposing stress [27]. From a variety of core stability tests [45], we selected two symmetrical endurance tests [46] for the flexors and extensors and one performed unilaterally from both sides to ensure a complete multi-dimensional muscle assessment of the thoracic spine, the lumbopelvic hip complex, and the abdomen. We included a hip abductors strength test, which seems to be correlated with non-contact lower limb injury [46]. Most of the functional variables we introduced did not play a role in group separation. This might imply that other tests could be tested in future studies. Despite that, the finding that LESS was a significant predictor of group separation suggests that a more technique-focusing assessment of unilateral landing is fundamental for a proper pre-season ACL injury risk screening. Muscle fatigue has been suggested to alter landing biomechanics, predisposing the lower limb to ACL injuries [47; 48; 49; 50]. Performance in muscle endurance tests reflects the athlete's ability to resist fatigue and this was the reason for inclusion of these tests in the PA [27]. It might be useful to include such tests within the criteria for risk-level classification of athletes; however, muscle endurance has not been studied as an ACL injury predictor enough to provide cutoff values, as it applies to thigh muscle strength and hop tests. In the present study, the frontal core muscle endurance performance was a separating variable between high- and low-risk players indicating a direction for future investigation. It appears that the tested battery of criteria significantly classified players and could be useful for pre-season ACL risk assessment of football players. It was not directly tested for its injury-predictive potential, but the criterion in every single factor was the most widely accepted. Discriminant analysis showed that the overall successful classification was very high. It is important that our test-battery placed players into the low-risk group with higher accuracy than in the high-risk group. Only four players were misplaced in this category. Should the opposite occur, a higher number of them would be falsely considered safe for exposure to unrestricted participation in football, with an increased chance of being injured. A higher proportion of players were misplaced in the high-risk category, which is a possible error towards the safe side, accompanied by extra attention for those who might not need it. A question is raised regarding the approach to prevent these misclassifications. Observation of these particular cases, since the low number would not provide safe statistics, shows that the key variable for further consideration is the LESS score. For the four players that were initially considered safe, but in fact, may need a closer attention, we noticed that their mean functional asymmetries were low, while the LESS score marginally missed the upper limit of six mistakes (5.83). On the contrary, those who entered the high-risk group, but possibly belonged to the other group, had a mean of low LESS scores (4.69).