# Profiling of Physical Qualities of Highly Trained Portuguese Youth Soccer Players
## 1 Introduction  
The profiling of soccer players highlights physical, physiological, and anthropometric characteristics [1, 2, 3]. Previous studies have reported significant differences regarding running performance and strength capacities between players of distinct age categories andplaying positions [4; 5]. Indeed, elite soccer players have shown better physical performance compared to their non-elite counterparts, whether at senior level or in youth categories [6]. This information is highly valuable for coaches and sports scientists since it enables the assessment and comparison of players' physical capacities, regardless of their playing position or competition level [1]. Consequently, it supports the process of individualization during training prescriptions and load monitoring without disregarding the natural predisposition of some players to exhibit greater or lesser capacity in specific performance metrics [7]. In soccer, the profiling of players is intimately related to the profile of games and training practices, especially concerning the player's field position and age category. Indeed, significant differences between playing positions and age categories in soccer players across different physical qualities were previously reported [8; 9], demonstrating the necessity of coaches to individualize training prescriptions. Soccer is characterized as a high-intensity interval-based sport, which requires a blend of skills such as speed, agility, endurance, and strength [10]. The most decisive actions in soccer depend on maximal strength and anaerobic power generated by the neuromuscular system, which is directly linked to the capacity for force production [11]. It has been suggested that the Isometric Mid-Thigh Pull (IMTP) test is effective for assessing maximum strength due to its validity, reliability, simplicity, and low risk [12]. Previous studies have reported that isometric tests such as the IMTP are well-suited for daily soccer routines since it results in minimal muscle damage compared to eccentric-based tests [13], which are commonly used for stratifying strength training programs, and serves as an index of fatigue [14]. Moreover, IMTP performance has been correlated with sprint performance, which is highly correlated with peak speed in professional English youth (U23) soccer players [12]. IMTP absolute peak force has shown greater differences in higher age categories, with moderate to large effect sizes (\(d\) = 0.62 to 1.66), and the largest effects observed in the highest age groups [15]. Jumping and sprinting abilities are widely used as indicators of neuromuscular fitness in youth players and as talent identification markers to differentiate between elite and non-elite soccer players [16]. Although jumping movements are not the most frequent in soccer matches, analytical testing involves lower technical complexity compared to sprinting and change of direction movements while providing distinct performance parameters. Vertical jumping, in particular, reflects lower-limb muscular explosive strength and is useful for monitoring training-induced adaptations [17; 18]. Common exercises for evaluating rapid strength include the Countermovement Jump (CMJ) and Squat Jump (SJ) [19]. It has been reported that stronger players (measured via the IMTP) have demonstrated better CMJ performance [12]. Sprinting is another critical action that can determine the outcome of a soccer game. Indeed, straight sprints are the most dominant actions in scoring situations, with the majority performed without the ball, emphasizing the importance of assessing sprint performance [20; 21]. Previous studies reported significant differences between age categories in sprinting performance [22]. Moreover, it has been shown that elite young soccer players are faster, stronger, and show better jumping performance than their non-elite counterparts [23].