# Assessing External Peak Physical Demands in Under-19 Years and Professional Male Football
## 1 Introduction  
Football is one of the most technically and physically demanding sports [1, 2]. Players are required to cover large distances while performing decelerations, accelerations, and continuous changes of direction [3]. Over the past decade, the physical profile of the modern game has evolved considerably, with a growing emphasis on high-intensity efforts [4]. These actions are increasingly decisive in key phases of play and have led to a notable rise in the volume and frequency of high-intensity activities per match. However, these efforts are not entirely linear or continuous; instead, they are distributed in short bursts or mini-matches throughout the game [5]. Traditional analyses based on average match values often underestimate the intensity of these critical moments, potentially obscuring the actual physical demands placed on players. To address this limitation, recent research has adopted time-based analysis methods using moving time windows such as 1 min and 5 min epochs [6]. Studies in this area consistently show that as the analyzed time interval increases, the relative intensity of all variables and positions tends to decrease, though this reduction does not always follow a linear pattern [7]. To identify these external peak demands (PDs), it is useful to determine the most intense activity experienced by players for a selected variable across a specified time window of interest [8]. Different time windows have been used to measure these PDs, typically ranging from 1 to 10 min, showing that intensity decreases when the window exceeds 5 min due to accumulated fatigue [9]. In fact, some studies analyzing physical and technical performance following these PDs periods report a decline in total distance covered and high-intensity efforts, as well as in technical actions that are closely linked to physical exertion (e.g., running with the ball) [10]. Monitoring these PDs and understanding the match context in which they occur, as well as identifying the most affected positions and their specific demands, can significantly improve the interpretation and contextualization of the data. This, in turn, facilitates more personalized and informed decision-making in each situation. For instance, during these periods, central midfielders tend to cover more overall distance but spend less time at sprinting speeds, whereas forwards cover more sprint distance but less overall distance [11]. Moreover, previous studies have highlighted clear positional differences in worst-case scenarios across professional football, in both male and female cohorts [12]. These differences are especially notable in sprint-related metrics, where central midfielders consistently register lower values [12], while wide midfielders and full-backs typically record higher total distances and greater volumes of high-intensity running [12; 13]. Such insights further reinforce the importance of tailoring training loads according to positional demands. This allows physical trainers to monitor whether these intensity levels are reached, and, if not, to carry out specific adjustments to player training and recovery [14] to better prepare athletes in specific positions for these external PDs on match day [15]. While several studies are available, most have focused on professional male players [16], female players [12; 17], and elite U19 players [7]. However, comparisons between professional and youth players remain scarce. Understanding the physical differences can help identify the gaps young or nonprofessional players need to bridge to reach the professional level. In addition, this comparison can reveal which physical attributes are most important for success at the professional level, aiding scouts and teams in identifying promising players who exhibit those characteristics. This study aims to analyze these external PDs in U19 players from the top national division of this category, with an emphasis on potential differences in physical variables compared to their counterparts on a professional team.