## 1 Introduction
But in other studies, there was no correlation between physical tests and the running profile during the games [37; 38]. Based on the Yo-Yo intermittent recovery test level 1 and Yo-Yo intermittent recovery test level 2 (YoYoIE2) there is a correlation with the DIST, distance at medium speed (15-18 km/h), high speed (>18 km/h) and high intensity actions (>18 km/h) [23; 31; 39; 40; 41]. The playing position should be considered when the relation between fitness level and external load is being investigated [12]. A high fitness level can be beneficial for performance in football, but it is important to recognize the demands of each playing position (players with a high physical level do not necessarily cover the highest distance,because of their role and position in the game) [23; 39; 42; 43]. Furthermore, many factors can influence performance, such as running economy, lactic threshold and other morphological factors [44; 45]. Players of different positions have the same level of VO\({}_{2}\)max [46; 47], but using only VO\({}_{2}\)max as an endurance factor is disputed because anaerobic threshold (AnT) seems to be a better indicator for high intensity aerobic actions [48; 49; 50]. [PERSON] et al. [51], supported this for the players of different playing positions, as they found that the anaerobic threshold is a better endurance factor than VO\({}_{2}\)max. In the same vein, the speed during the lactate threshold can better discriminate players of different levels [45]. The correlation between the physical evaluation tests and the running distance through the games is not very clear, because it is dependent on the playing position. [PERSON] et al. [12] found low correlations for the defenders and the midfielders but high correlations for the attackers. Other authors found correlations only for central defenders [52], and in another study there were correlations for the central defenders and the attackers, but not for the central defenders and the side defenders [39]. The results from a recent study [47] showed that for the players on the wide positions (side defenders and wingers), there is a correlation between HSR (distance covered with speed \(>\) 19.8 km/h), distance covered with speed between 19.8 and 25.1 km/h (DIS5), distance covered with speed \(>\) 25.1 km/h (DIS6) and the AnT, and a correlation between distance covered with speed \(<\) 14.3 km/h (DIS \(<\) 4) and AnT, and distance covered with speed between 14.3 and 19.8 km/h (DIS4) and the aerobic threshold (AeT) for the players of the axon. Furthermore, for the side defenders, there was a correlation between AnT and HSR, DIS5, and DIS6, and between VO\({}_{2}\)max and DIS6. For the central defenders there was a correlation between AnT and DIST, DIS \(<\) 4, DIS5. For the central midfielders, there was a correlation between VO\({}_{2}\)max and DIST, DIS \(<\) 4, but negative with DIS5, and finally, between DIS \(<\) 4 and VO\({}_{2}\)max, AeT and AnT for the attackers. The purpose of this study was (a) to examine the differences on physical indexes between football players of various playing positions and (b) to investigate the correlations between the physical parameters and the external load during the in-season microcyles.