## 2 Materials and Methods
### Experimental Design  
In this study, players underwent testing at the Trabzon University Sports Performance Analysis and Talent Centre Laboratory. Before initiating the main testing phase, participantswere introduced to a preparatory session at the Trabzon University Sports Performance Analysis and Talent Centre Laboratory. The purpose of this session was to familiarise them with the testing setting, equipment, and specific procedures, aiming to secure consistent and precise data collection during the subsequent tests. The session acquainted participants with the COSMED K\({}_{5}\) portable gas exchange system for real-time VO\({}_{2}\) monitoring and provided instructions on using the handheld portable analyser for blood lactate (BLa) measurements, as well as the Garmin HRM-Run(tm) (Garmin Ltd., Olathe, KS, USA)) for continuous heart rate observation. These devices were chosen based on their validation in various studies and their ability to provide continuous monitoring at 1 s intervals. This method ensures minimal error and accurate heart rate data collection throughout the exercise phases [19]. Additionally, they engaged in preliminary runs of the cycling and running repeated sprint tests to familiarise themselves with the test structure, including sprint intervals and rest periods. We utilised the 6-20 Borg scale for the RPE. The 6-20 scale specifically allows participants to rate their exertion on a continuum from 6 (no exertion at all) to 20 (maximal exertion). To address the subjectivity concerns, we conducted a thorough familiarisation session with the participants, ensuring they were comfortable and consistent in using the scale. This session aimed to minimise variability and enhance the accuracy of the perceived exertion ratings [20]. This initial session was crucial for ensuring participants were thoroughly informed and comfortable with the study's methodologies, thereby reducing potential variations in test outcomes attributable to unfamiliarity with the process. The testing consisted of a familiarisation session and two testing sessions, each conducted 48 h apart, and at the same time of day. The two testing sessions consisted of a running repeated sprint test, and a cycling repeated sprint test, respectively. The players were required to complete a cycling repeated sprint test and a running repeated sprint test on two different occasions. Each session was scheduled in the morning, specifically between 9 and 10 o'clock. During these tests, VO\({}_{2}\) levels were monitored in three phases: a 10 min rest period, the exercise phase, and a 15 min recovery phase, where the measurements were taken while the subjects were seated. Rate of perceived exertion (RPE) was assessed directly following the tests. Monitoring was carried out in breath-by-breath mode using the COSMED K\({}_{5}\) portable gas exchange system (Rome, Italy). The study by [PERSON] et al. (2018) provides significant findings on the validity, reliability, and minimum detectable change of the COSMED K\({}_{5}\) portable gas exchange system. The research thoroughly examined the device's capability to measure in \"breath-by-breath\" mode and found it to have a high correlation with reference systems (r > 0.90). Additionally, the device demonstrated high internal consistency in repeated measures (ICC > 0.85), and the minimum detectable change, calculated using the standard error of measurement (SEM), indicated the device's ability to detect small changes. These findings support the use of the COSMED K\({}_{5}\) as a reliable and valid measurement tool in both clinical applications and sports sciences [21]. Calibration of the gas analyser was performed before the tests using a known gas sample (5.0% CO\({}_{2}\) and 16.0% O\({}_{2}\)). Blood lactate (BLa) values were measured using a handheld portable analyser (Lactate Plus, Nova Biomedical, Waltham, MA, USA). The study by [PERSON] et al. (2013) provides critical insights into the validity and reliability of the Lactate Plus analyser [22].