Validation of Blood Oxygen Level Test in Well-trained Athletes

The study participants rested for 15 minutes before measuring the BOLT score. During this time they were carefully instructed on how to perform the measurement. It was underlined that we do not measure how long one can hold their breath, but the time it takes for the body to react to lack of air and feel the desire to breathe. After a few normal breaths through the nose, after the exhalation, the participants held their breath until they felt the first definite desire to breathe or felt the first involuntary contractions of the respiratory muscles. The first was assessed by the participants, the latter was also visually assessed by the researchers. The nose was closed with the fingers to prevent any gas exchange. The researchers measured the time with a Finis 3x300M stopwatch (FINIS USA, Livermore, CA, USA). Time in seconds, to one decimal place, was noted as a BOLT score. The visualisation of BOLT is presented in Figure 2.

WAnT was conducted with Monark 874E Cycle Ergometer (Monark Exercise AB, Sweden). Before WAnT, the participants performed a 5-minute warm-up with resistance ranging from 0.8 to 1.2 W/kg. Next, the participants performed a maximal 6-second sprint, with the resistance adjusted to 7.5% of the individual body mass. After a rest interval of 2 to 5 minutes, the participants underwent a 30-second WAnT with resistance set at 7.5% of the individual body mass. They were instructed to attain the highest peak power output as quickly as possible and maintain the highest power output throughout the entire duration of the test. The participants received motivating and enthusiastic verbal support. The following indices were measured and included in the further analysis: peak power (Ppeak), total work (TW), WSSR. All the indices were calculated with the dedicated software (MCE 6.0, JBA Z. Staniak, Poland) linked to the cycle ergometer.

CPET was performed with the Cortex Metamax B3 (Cortex Biophysik GmbH, Leipzig, Germany), breath-by-breath method, and Cyclus II Ergometer (RBM, Leipzig, Germany). Participants underwent an incremental ramp test, commencing at 55-70W and incrementally increasing the load by 0.17-0.28 W·sec-1, individually adjusted for body mass. The participants were instructed to continue the effort until total exhaustion. All the participants fulfilled the maximum effort criteria (Wiecha et al. 2023): 1) respiratory exchange ratio ≥ 1.10, (2) present VO2 plateau (growth \< 100 mL·min-1 in VO2 despite increased cycling power), (3) respiratory frequency ≥ 45 breaths·min-1, (4) declared subjective exertion intensity during CPET ≥ 18 according to the Borg Scale (Borg 1998), (5) blood lactate concentration ≥8 mmol·L-1, (6) peak heart rate ≥ 15 beats·min-1 below predicted maximal heart rate (HRmax) (Lach et al. 2021).