## 1 Introduction  
In football, as in most sports involving ball handling, athletes develop a preference for using one of their legs to control the ball. Typically, a football player uses their dominant leg to shoot and pass the ball, while the other leg is considered the non-dominant leg [1]. The choice of the dominant leg often influences the player's position on the field. However, in addition to movements involving the ball, most movements made by football players during matches or training sessions are performed without the ball and are characterizedby the preference for the dominant leg [2; 3]. Such movements include changes of direction, take-offs for jumping, faints, and tackles, among others.  
Over time, this preference has been shown to lead to asymmetries between the limbs in performance on specific physical tests (e.g., single-leg jumps, isokinetic strength measurements) [4]. When these asymmetries exceed 15%, they have been associated with an increased risk of injury [5; 6] as well as a negative impact on athletic performance [7; 8; 9; 10; 11]. These asymmetries have been observed at all levels of football players, including professionals, amateurs, and youth players [11; 12; 13].  
Over the years, various tests have been used to detect asymmetries, such as isokinetic strength measurements [14; 15], vertical jump tests [8; 16], horizontal jump tests [7; 17; 18], and strength exercises (e.g., back squat) [19]. However, it should be noted that these tests differ significantly from each other. For example, the assessment using an isokinetic dynamometer focuses on one joint and measures different types of strength depending on the speed of movement, whereas a jump test is a multi-joint test that evaluates the power/jumping ability of the athlete's lower limbs. Therefore, the appropriate test should be chosen depending on the specific goal.  
Among these tests, the isokinetic dynamometer is the most reliable for assessing strength asymmetries. However, this test requires specialized personnel for administration, is time-consuming, and has high costs, which means it is not frequently conducted by teams for all their players. In contrast, tests that involve single-leg jumps can be conducted with much more affordable equipment, require less specialized expertise from the evaluator, and are much quicker. Additionally, many jumping tests are part of the weekly routine for football teams. Thus, if there was a relationship between the detection tests (isokinetic evaluation and jump tests), it would be possible to detect not only strength asymmetries but also asymmetries in various forms of strength using a jumping test.  
This approach could help identify asymmetries in the lower limbs (across a broader spectrum of physical abilities, maximum strength, power-speed, and strength endurance) as part of the weekly routine for football players, enabling the implementation of individualized programs before these asymmetries affect performance or become a risk factor for injury.  
Therefore, the aim of this study was to examine the relationship between the asymmetries observed in the application of the single-leg countermovement jump (SLCM)) and those observed through isokinetic strength assessment at 60\({}^{\circ}\)/s, 180\({}^{\circ}\)/s, and 300\({}^{\circ}\)/s in high-level youth football players. We hypothesize that the asymmetries observed in the SLCM] will be positively correlated with the asymmetries observed in the isokinetic strength evaluation (60\({}^{\circ}\)/s, 180\({}^{\circ}\)/s, and 300\({}^{\circ}\)/s), and particularly at 300\({}^{\circ}\)/s, which is an indicator of the lower limb's power-speed.