## 2 Materials and Methods
### Procedures  
Body composition measurements: A wall stadiometer (The Leicester(r) Height Measure, Tanita(r), Tokyo, Japan) was employed to measure the stature of the footballers, and the Tanita scale and body fat analyzer (BC 418 MA, Tanita(r),Tokyo, Japan) were used for their mass. Their body composition was analyzed using the 7-site skinfeld method [27] with a skinfeld caliper (Skyndex(r), Greenwood, SC, USA).  
Cardiopulmonary exercise testing (CPET): The laboratory temperature was controlled throughout all testing sessions at 20 \(\pm\) 2 \({}^{\circ}\)C, and the relative humidity was approximately 50%. The testing protocol included 3 min running increments with a consistent incline of 1%, which is considered optimal for offsetting the absence of air resistance in the laboratory environment [28]. Specifically, a motorized treadmill (h/p/Cosmos(r) Quasar med, H-P-Cosmos Sports & Medical GmbH, Nussdorf-Traunstein, Germany) was programmed using the Cosmed Quark(r) CPET (Rome, Italy) system's software (Omnia Software 2.3, Rome, Italy) to start with a velocity of 8 km/h and speed up 2 km/h every three minutes and 15 s. The 15 s interval was the dead time that allowed subjects to pause the activity for lactate sampling purposes, thus ensuring that the activity for each increment lasted for three minutes. Breath-by-breath pulmonary gas exchanges were collected using reusable rubber masks (model 7940, [PERSON], Kansas City, MO, USA) and analyzed using the Cosmed Quark(r) CPET metabolic analyzer (Rome, Italy). The heart rate (HR) was continuously monitored using a Polar H10 chest strap sensor (Polar(r) Electro Oy, Kempele, Finland). The breath-by-breath data analysis involved filtering the data using 10 s averages to smooth them and accurately determine the \(\dot{V}\)O\({}_{2}\) max. The criterion for exercise cessation was volitional fatigue, and those for the \(\dot{V}\)O\({}_{2}\) max determination were (a) a plateau in \(\dot{V}\)O\({}_{2}\) max, (b) an accumulation of more than 8 mmol/L, and (c) a respiratory exchange ratio (RER) greater than 1.10 [29]. The exercise intensity that is appropriate for accurately assessing running economy (RE) is specified at speeds below 85% of the \(\dot{V}\)O\({}_{2}\) max [30]. Thus, similar to [PERSON] et al. (2011) [17], we calculated RE using the average \(\dot{V}\)O\({}_{2}\) of the last 30 s while running at 12 km/h.  
Lactate sampling: Lactate sampling utilized 28G, 1.8 mm side fire single-use safety lancets (Unistik(r) Comfort, Owen Mumford Ltd., Woodstock, Oxfordshire, UK) to perform finger picks, preferably on the 3 rd and 4 th digits according to the methodology described by previous investigators [31]. Blood lactate analysis was conducted using a validated [32] analyzer (Lactate Plus(r), Nova Biomedical, Waltham, MA, USA) equipped with a disposable 0.7 uL lactate strip. Before each test, the lactate analyzer was calibrated using Lactate Plus(r) control solutions to ensure accurate and valid data. In total, 554 capillary blood lactate samples were collected. The blood lactate concentrations during incremental testing were plotted against the running speed. The validated software \"Lactate-E, v2.0\" (Galway, Ireland) [33] was used to calculate each player's lactate thresholds using the VI [18], log-to-log transformation [19], Dmax [20], and 4 mmol/L FBLA [21] methods.