## 5 Conclusions  
This study determined the difference between external and internal load in several time parameters (T1: 0-45 min, T2: 45-70 min, T3: 0-70 min, T4: 70-90 min, T5: 45-90 min, and T6: 0-90 min) of elite youth (U17 and U19 age category) soccer matches with GPS running performance and HR response. The main findings were observed in both EL and IL parameters between the first 70 min (T3) and the last 20 min of the match (T4), and between the first half (T1) and the second half (T5). A decrease in HMLD in the last T4 was up to 17.7% compared to T3. Moreover, players' performances in highest heart rate zone (HR\({}_{Z5}\)) in T4 phase was just 17.85% compared to 27.05% in the T3 phase. Because of these facts, we must implement soccer-specific training of small sided and large games to be able maintain high intensity performance during the total match duration. On-field demands, specific player load, and youth physiological adaptability to the soccer match are the most important determinants for setting up a soccer training strategy. Factual results of players' loads are the basis for designing team, group, and individual training programs in all team-based sports. Monitoring of the player's load could also give us the opportunity to improve the aerobic and anaerobic capacity at the start of the youth elite player's season and to get progressive results at the end of the season macro-cycle. The present study may enhance the process of training and help improve players' fitness levels. Furthermore, it could be beneficial for improving individual player monitoring during matches and, thus, help substitute faster players who do not fit in the tactical play and help change the play. Our data could also be beneficial when comparing youth players to professionals, in situations such as young players graduating to their club's first-team squad.  
Conceptualization, E.K., T.M. and F.Z.; methodology, T.M. and K.R.F.; software, E.K. and M.H.; validation, D.S., A.B. and F.Z.; formal analysis, D.B., A.B. and F.Z.; investigation, E.K., T.M. and M.H.; resources, E.K. and L.M.; data curation, E.K. and M.H.; writing--original draft preparation, E.K.; writing--review and editing, K.R.F., D.S., L.M. and A.B.; visualization, T.M., D.B. and M.H.; supervision, T.M., D.S. and K.R.F.; project administration, F.Z., L.M. and T.M.; funding acquisition, T.M. and F.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by GACR19-12150S, UNCE HUM 32 and Cooperatio: Sport Sciences--Biomedical and Rehabilitation Medicine.  
The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board (or Ethics Committee) of Faculty of Physical Education and Sport, Charles University in Prague, Czech Republic (Nr. 101/2018).  
Informed Consent Statement:Informed consent was obtained from all subjects involved in the study. The design was explained to all participants and informed consent was collected from players, or the players' parents if the players were younger than 18 years old, before assessments were performed. The study was approved by the Ethical Committee of the Faculty of Physical Education and Sport, Charles University, in Prague, Czech Republic (Nr. 101/2018).  
Not applicable.  
Conflicts of Interest:The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.