## 5 Conclusions  
This study elucidated the similarities and differences in energy system contributions and performance outcomes between cycling and running repeated sprint protocols with comparable total sprint times and work-rest ratios. The key findings reveal that running repeated sprint tests elicit a higher energy demand and a greater contribution from the phosphocreatine (PCr) energy system compared to cycling. Specifically, running tests demonstrated significantly higher values in TEE, energy demand, and PCr-related metrics, which underscores the greater anaerobic demand associated with running sprints. The performance variables showed distinct differences between the modalities, with a higher PP and MP observed in the cycling tests, while the FI was notably higher in the running tests. These differences suggest that running and cycling sprints impose different physiological demands and may not be used interchangeably for assessing RSA in athletes, particularly in sports such as soccer where running is more prevalent. The association between the performance variables and energy system contributions was also explored. The ATP-PCr system showed a significant correlation with peak power outputs, highlighting its crucial role in high-intensity, short-duration efforts. The glycolytic system's contributions were consistent across both modalities, while the oxidative system played a minimal role during the sprints but was essential for recovery.  
Future research should aim to explore several key areas to enhance our understanding of the energy system contributions and performance metrics in repeated sprint tests. Longitudinal studies investigating the long-term effects of specific training programs on the energy system adaptations and RSA performance in different sports modalities are essential. Additionally, studies measuring the real-time lactate dynamics and oxygen consumption during exercise will provide a more comprehensive understanding of the metabolic contributions. Developing and validating sport-specific RSA testing protocols that closely mimic actual performance demands and fatigue profiles experienced during competition is crucial. Furthermore, examining the effects of varying recovery intervals (active vs. passive) on performance outcomes and energy system contributions will help optimise training regimens for different sports. Finally, integrating advanced wearable technology for the continuous monitoring of physiological parameters can enhance the data accuracy and applicability in real-world settings. These research directions will aid in designing more effective training programs tailored to the specific needs of athletes, thereby improving performance and reducing injury risk.  
Conceptualisation, E.T. and G.D.; methodology, G.D. and E.T.; validation, G.D. and E.T.; formal analysis, G.D. and E.T.; investigation, G.D. and E.T.; resources, G.D. and E.T.; data curation, G.D. and E.T.; writing--review and editing, G.D. and E.T.; visualisation, E.T.; supervision, E.T. All authors have read and agreed to the published version of the manuscript.  
This study was funded by the Trabzon University Research Fund (22 HZP00211).  
The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of the University of Trabzon (resolution 4 October 2022). Before the study, written informed consent to participate in the study was obtained from all the participants.  
Informed Consent Statement:Informed consent was obtained from all subjects involved in the study.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The author thanks the athletes who participated in this study.