## 4 Discussion
Thus, in this study, a connection is demonstrated between total distance and high-intensity running and cardiorespiratory endurance. The explanation of these results is based on the observation that the cardiorespiratory endurance of footballers is a crucial factor for success in football matches. From a physiological perspective, better cardiorespiratory endurance in footballers is directly linked to the development of the cardiovascular and respiratory systems' ability to maintain oxygen delivery to actively engaged muscles during prolonged physical activity, as well as the muscles' ability to obtain the necessary energy through aerobic processes [82; 83]. Accordingly, footballers who have shown better results in HR and VO2 parameters, as measures of cardiorespiratory system functioning, achieved greater distances in high-intensity activities and in the overall distance covered. The physiological explanation implies that footballers with greater cardiorespiratory system capacities are able to maintain lower heart rate values at the same running speed, as indicators of system load. In other words, even at the same running speed, the physiological load on the body varies. Our study has shown, through parameters such as HR max and HR AT, that players who achieved higher values of maximum heart rate, as well as lower values of heart rate at the anaerobic threshold, covered a greater total distance and had greater distances in high-intensity activities (above 19 km/h). On the other hand, the HR 2\({}^{\prime}\) parameter indicates that footballers with lower heart rate parameters during recovery have cardiovascular system capacities to recover faster from intensive activities, which is very important as football involves alternating periods of work and rest. It is recognized that high-intensity running is of great importance for performance in elite football [84; 85], as numerous studies have shown that this parameter is discriminative between players at higher versus lower levels of competition [86; 87]. High-intensity periods during football matches impose high demands on footballers' bodies, leading to the increased involvement of the anaerobic energy system, with the accumulation of lactic acid and decreased pH values in exercising muscles [71]. The cumulative effects of numerous high-intensity stimuli lead to higher concentrations of lactic acid in the blood of footballers [88]. Therefore, good aerobic fitness of players is important, as it enables better plasma flow through the system, requiring faster removal of harmful metabolic by-products [89] and thus accelerating recovery between intermittent stimuli, while good anaerobic capacity compensates for the high intensities required during play [73]. In our study, a relationship between lactate and MRP was lacking, suggesting that the methodology for assessing lactate and movement performance should be reconsidered. Specifically, from a methodological standpoint, the site of blood sampling for lactate concentration measurement and the laboratory methods used can also influence test results. The authors in [90] suggest that the most accurate approach would be to take blood samples from working muscles, which is not the case in our study. Regarding movement performance, it is noted that other factors related to the complexity of football matches can influence the achieved result. Primarily, these include the playing formation [4], opponent [90], ball possession [91], and the technical level of the footballers [92]. This indicates that some players with high physical capacities do not cover great distances due to the tactical limitations of their role in the team. This study represents a significant contribution to understanding the impact of cardiorespiratory and metabolic parameters on the MRP of professional football players. One of the key strengths of this research is that the findings have determined which cardiovascular, respiratory, and metabolic parameters are most strongly associated with various running speeds of football players.