Lactate and pyruvate concentrations
COLD
We collected blood samples at rest and immediately after exercise. For the pyruvate samples, we drew 1 mL of venous blood into EDTA tubes (Bd Vacutainer K2E 5.4 mg Bd-Plymouth, UK). Then, within 1 min, we pipetted 0.5 mL of blood into two pre-chilled tubes containing 1 mL of 8% perchloric acid each. We cooled the perchloric acid tubes by placing them into a container with cold gel packs for 5 min and then centrifugated them for 10 min at 4 °C and 1500 G. We pipetted the resulting supernatant into one perchloric acid tube. For the lactate samples, we drew 0.5 mL of venous blood into fluoride oxalate tubes (Vacutest NaF + K2OX, Vacutest Rima, Italy), which we then centrifugated for 10 min at 3000 rpm. Both samples were next placed in a freezer at -20.5 °C for a maximum of 3 days and then moved in dry ice to the Helsinki University Hospital Laboratory (HUSLAB) for analysis. The pyruvate samples were analyzed enzymatically by photometry, and the lactate samples were analyzed photometrically. We calculated lactate-to-pyruvate (L/P) ratios for each participant.