## 4 Discussion  
To the authors' knowledge, this is the first study to predict the potential determinants of LBK performance (maximum horizontal distance) and to determine the target training cut-off for LBK performance in young soccer players. Before answering both objectives based on the data obtained, kicking is a complex biomechanical sequence in which the foot contacts the ball [27], and both the speed and accuracy of the kick are determined by the resultant forces applied to the ball as it interacts with the foot [27; 28]. Unsurprisingly, both the speed and accuracy of kicking improve with the physical and technical development of players [2; 5]. Soccer kicking has been the subject of scientific research for more than 50 years, but no studies have been found to determine the values of predictors of performance in LBK training as a guide for training. An LBK refers to a pass, a shot or a clearance that is classified according to the distance the ball travels [29]. In particular, pass and shoot in soccer are classified into two (short and long) or three (short, medium and long) categories [29; 30]. [PERSON] et al. classify a short pass as being from 0 to 10 m, a medium pass as being from 10 to 20 m and a long pass as being more than 20 m for formative-stage players between the ages of 7 and 16 years [29]. [PERSON] et al., who analysed the performance frequency of selected technical activities in international soccer players during UEFA Euro 2016, defined long pass and short pass quantitatively at a cut-off of 22.86 m (25 yards) [31]. After studying the changes in technical and physical performance between the first and second half of official Italian Serie A matches, [PERSON] et al. proposed the cut-off between short pass and long pass at a distance of 37 m in 186 soccer players with an average age of 27 years [32]. [PERSON] et al., who investigated the effect of bio-banding upon physical and technical performance of youth soccer players (11-15 years), establish the cut-off between short and long pass at 20 m and stated in their definition that the pass is directed to his teammate and that he successfully controls the ball [30]. In the present study, the long pass at a distance of 30 metres or more was determined on the basis of the participants' results and the subsequent statistical analysis according to the homogeneity criterion (k-means cluster) for players aged between 12 and 18 years. The proposal by [PERSON] et al. could be more interesting, as they analyse the physical and technical performance of players according to their biological maturity and age rather than their chronological age. Executing an LBK involves kicking the ball with power and precision. This requires activating the muscles of the lower limbs, such as the iliacus, quadriceps, gluteus, adductors, hamstrings, gastrocnemius and tibialis anterior [33; 34]. Maximising ball speed is a key element for LBK success [5; 6; 35], which depends on various factors such as age, skill level, approach angle and lateral dominance [2; 3; 6]. In the present study, age, kinanthropometry, hip and knee range of motion, and strength were factors associated with LBK performance. However, age was the most important predictor that distinguished the players with a ball kicking of more than 30 metres. These results are consistent with those found in previous research studies of one hundred and six young elite soccer players (12-15 years) [2], adult (male and female) [3] and male pubertal players [3]. On the contrary, no differences in soccer background were found depending on the cut-off point of ball kicking performance (\(\geq\)30 m). However, the training load of soccer players in different age categories (U-12, U-15 and U-23) [36] and differences in anthropometric and physical fitness variables (handgrip strength, flexibility, vertical jump, countermovement jump, sprints and agility \(t\)-test, and repeated sprint ability 15 \(\times\) 15 m) variables based on chronological age (7 and 15 years old) in young soccer players [37; 38].