*2.4. Erythrocyte Isolation and Blood Collection*

At rest and immediately after the GXT, a 10 mL blood sample was collected from the antecubital vein via clean venipuncture (20-gauge needle) and added to a tube with ethylenediaminetetraacetic acid (EDTA, 4 mM). Blood cells were counted by using a Sysmex SF-3000 cell counter (GMI Inc., Ramsey, MN, USA), and the blood pH and lactate concentration were tested by an i-STAT handheld blood analyzer (Abbott Point of Care Inc., Princeton, NJ, USA). Erythrocytes were isolated from whole blood by centrifugation (1000× *g* for 15 min at RT), the supernatant was discarded, and the buffy coat was discarded, followed by three washing steps in PBS with 0.1% (*w/v*) glucose (Sigma). The erythrocyte count was adjusted to 1 × <sup>10</sup><sup>4</sup> cells/μL using PBS.
