## 4 Discussion
A study involving elite Danish football players found no significant difference in VO\({}_{2}\)max between regular starters and non-regular first-team members, suggesting that this physiological measure alone may not be a decisive factor for high-level performance in football [24; 53]. However, it should also be added that numerous studies have reported a large variation in VO\({}_{2}\)max, which is relatively associated with the different positions of the football players within the team. The obtained results of the Danish professional footballers indicate that fullbacks and midfielders appeared to have the highest VO\({}_{2}\)max values, and goalkeepers and central defenders the lowest [11]. However, the results of the other studies indicated that the VO\({}_{2}\)max values of football players who competed at the same level of the league and played in different positions were close to each other [17; 71]. In contrast, this study did not take into account the players' positions on the field, which may also have had an impact on the results obtained. The results emphasize the physiological differences between TR and MR football players based on the different demands on the body in professional football and the adaptations needed for those competing at the highest level. There were significant differences in the cardiorespiratory metrics between the TR and MR players. The TR players showed lower heart rate values at the anaerobic threshold (HR AT and HR AT\(\%\)) and superior performance in the second minute of recovery (HR 2\({}^{\prime}\) and \(\%\)Re 2\({}^{\prime}\)). The results show that players from leading teams had better-developed aerobic and anaerobic energy systems, using energy more efficiently during the high-intensity efforts and recovering faster during the low ones. Adaptations such as these are critical for sustaining performance in match play involving rapid transition between energy systems [72; 73]. Conversely, the MR players exhibited significantly higher VO2 max and related indices (VO2 max/v and VO2 max/HR). This may reflect a physiological adaptation to playing styles that rely heavily on endurance-based strategies, such as increased ball recovery and defensive responsibilities. Previous research has implied that less successful teams often perform more high-intensity running and cover greater distances, requiring robust aerobic systems to sustain performance levels [74; 75; 76]. The findings provide practical guidance for designing team training programs with strategies for teams and attending to player roles. Even the baseline features of cardiac capacity (HRmax, \(\%\)Re 1\({}^{\prime}\)) were not significantly different between the groups, suggesting equivalent cardiac potential. However, the TR players' superior recovery metrics and cardiovascular efficiency give them a competitive advantage. The key takeaways arise from this interplay between physiological capacity and tactical execution, in which elite football performance is defined [77; 78; 79]. The fact that TR players exhibited superior recovery and metabolic efficiency despite lower VO\({}_{2}\)max scores underscores the importance of integrated fitness attributes beyond pure aerobic capacity. These nuanced physiological adaptations are likely shaped by training specificity, tactical strategies, and overall team structure. Metabolic parameters showed fewer differences between TR and MR players. Both groups exhibited similar lactate concentrations at rest and during recovery phases, except for the metabolic efficiency index (Index ME), which was significantly higher in TR players. This suggests that TR players are better equipped to optimize metabolic processes during high-intensity activities, allowing them to sustain performance while minimizing fatigue-inducing byproducts, such as lactate [80; 81; 82]. Consistent lactate levels across both groups indicate consistent anaerobic capacity within the league.