## 1 Introduction  
To enhance the likelihood of success in soccer, a comprehensive approach to player preparation is essential, encompassing the technical, tactical, physical, and psychological dimensions [1]. The physical dimension of soccer has gained significant importance in recent years [2], considering soccer's nature as a highly demanding team sport [3]. The physical profile in soccer is marked by a multitude of high-intensity actions, including sprints, directional changes, jumps, and accelerations/decelerations [4]. These high-intensity actions are closely linked to soccer performance, with sprints being particularly common in goal-scoring situations [5]. Consequently, strength and conditioning coaches are keen on ensuring the optimal preparation of players to meet these demands. To achieve this goal, various strategies have been employed, with workload monitoring [6] standing out prominently [6]. Traditionally, this approach involved the use of video data, typically obtainable only in stadiums equipped with video camera systems, to monitor the distances covered by soccer players during matches [7]. Conversely, during training sessions, only internal load metrics such as heart rate or perceived exertion could be assessed [8]. However, with the International Federation of Association Football (FIFA) now allowing the use of Global Positioning System (GPS) devices in official competitions [9], soccer clubs have integrated these devices into their facilities, enabling the monitoring of training sessions as well [10]. This strategy not only facilitates understanding the applied workload during training sessions but also enables the monitoring of sport-specific metrics of external load during matches, allowing for a comparison with training workload [11]. Additionally, GPS devices also permit the monitoring of workload throughout the entire microcycle, enabling comprehensive periodisation based on each variable and optimising training effects. Despite this, modern soccer is characterised by chaotic and frequently changing schedules due to various factors, including television rights and progression through knock-out tournaments [12]. This results in many congested microcycles during the season, where the team plays more than one game per week, making it difficult to conduct sufficient training sessions during the in-season period [11]. Additionally, most of these training sessions are focused on post-match recovery or tapering for the subsequent match [13; 14]. Thus, from a physical fitness perspective, the pre-season has gained relevance, as during this period [15; 16], strength and conditioning coaches have more training time focused on physical fitness, temporarily overloading athletes' biological systems to elicit positive physiological adaptations [17]. To date, only one study has analysed the external workload imposed on professional soccer players during a pre-season [18], but these authors only considered friendly matches for this quantification. Therefore, a more comprehensive analysis of the pre-season, including training sessions and friendly matches, is required. In this regard, this study aimed to describe the workload during a 6-week pre-season in Belgian professional soccer players and to analyse and compare the workloads of players in each microcycle according to several variables of external workload (e.g., distance covered at some velocities). Seventeen male Belgian professional soccer players competing in the second division of the Belgian league system participated in this study. We hypothesised, based on general training theory [19], that lower values in most variables are found in week 1, with progressive increases during the central part of the in-season, and stable values at the end of it, although with differences according to each external workload metric.