## 2 Materials and Methods
### Material and Testing  
For descriptive purposes, participants' height (cm) and body mass (kg) were determined using a precision stationmeter and a weighing scale (SECA 222 and 634, respectively, SECA Corp., Hamburg, Germany). Additionally, body fat (mm) was also calculated as the sum of 6 specific point skinfolds (i.e., subscapular, triceps, abdominal, supraspinal, iliac crest, and front thigh) using a slim guide skinfold caliper (Harpenden, British Indicators, Burgess Hill, West Sussex, UK). All instruments were adjusted before their use and measurements were taken following the guidelines of the International Society of the Advancement of Kinanthropometry (ISAK) [26]. A description of participants' characteristics is available in Table 1.  
\(\dot{\mathrm{VO}}_{2}\) and \(\dot{\mathrm{V}}\mathrm{CO}_{2}\) during the trials was recorded using a portable gas analyzer (Cosmed K5, L.L.C. Rome, Italy) in breath-by-breath mode [27]. Before conducting any tests, the K5 was calibrated in line with the manufacturer's guidelines, which are as follows: (1) calibrating with room air, (2) calibrating the flow meter with a 3-L syringe, (3) calibrating the scrubber to zero the \(\dot{\mathrm{CO}}_{2}\) analyzer, (4) calibrating with a reference gas consisting of 16% oxygen (\(\dot{\mathrm{O}}_{2}\)), 5% carbon dioxide (\(\dot{\mathrm{CO}}_{2}\)), and 79% nitrogen (\(\dot{\mathrm{N}}_{2}\)), and (5) performing a delay calibration specifically for the breath-by-breath mode. Data collection was averaged each 15 s to smooth the graphs and facilitate the detection of inflection zones. Subsequently, \(\dot{\mathrm{VO}}_{2}\)max and ventilatory thresholds 1 and 2 (VT1 and VT2) were individually determined for each runner according to the V-slope method proposed by [PERSON] et al. and described elsewhere [28; 29]. All physiological determinations were performed independently by one investigator in a blinded manner (i.e., without knowing to which subject and which overload condition the test corresponded), with two cases of failed detection and the breath-by-breath data from another participant ultimately being removed due to equipment malfunctions during one test. Additionally, the respiratory exchange ratio (RER) was also registered at VT1, VT2, and exhaustion. Capillary blood samples were taken from the fingertip one minute after the test to measure peak blood lactate concentration (\(\mathrm{La}^{-}\)), in mmol\(\cdot\)L\({}^{-1}\), using Lactate Scout+ \begin{table}
\begin{tabular}{c c} \hline \hline
**Variable** & **Mean \(\pm\) SD** \\ \hline Age (years) & 37.8 \(\pm\) 5.9 \\ Height (m) & 176.3 \(\pm\) 4.7 \\ Body mass (kg) & 72.2 \(\pm\) 4.9 \\ \(\Sigma\) 6 skinfolds (a. u.) & 65.8 \(\pm\) 15.0 \\ Training volume (km\(\cdot\)w\({}^{-1}\)) & 49.7 \(\pm\) 20.7 \\ Time in 10 km race (min) & 40.4 \(\pm\) 3.0 \\ \hline \end{tabular}
\end{table} 
Table 1: Descriptive characteristic of the participants (mean \(\pm\) SD). (EKF Diagnostics, Leipzig, Germany). Maximal exertion was defined by the following criterion [30]: (1) a discernible plateau of VO2, (2) [La+] \(\geq\) 8 mmol\(\cdot\)L\({}^{-1}\) or (3) RER \(\geq\) 1.10. Absolute mechanical power output (in W) and the mechanical power output normalized to body mass (in W\(\cdot\)kg\({}^{-1}\)) were registered with the Stryd\({}^{\mathrm{TM}}\) powermeter (Stryd powermeter, Stryd Inc., Boulder, CO, USA) attached to the runners' shoelaces. Despite the validity of Stryd not having yet been evaluated against gold standard methods, recent studies position it as the leading wearable sensor available, showing the highest level of agreement with theoretical methods of running mechanical power calculation [31] and measured metabolic power [23]. Data from Stryd\({}^{\mathrm{TM}}\) were extracted from the manufacturers' official website ([[https://www.stryd.com/eu/es](https://www.stryd.com/eu/es)]([https://www.stryd.com/eu/es](https://www.stryd.com/eu/es)) (accessed on 21 March 2024)) into separated.csv files.