Association between Yo-yo intermittent recovery test, physiological markers of endurance performance, and buffering capacity in professional soccer players.

The Yo-Yo Intermittent Recovery Test Level 1 (YYIR1) is widely recognized as a reliable tool for assessing intermittent endurance and aerobic capacity in team sports athletes. This study aims to verify the association between YYIR1 and physiological markers of endurance performance in professional soccer players, as well as the relationship between metabolic buffering capacity, metabolic acidosis tolerance, and YYIR1 total distance. Twenty-six professional soccer athletes (26.3±4.98 years, 76.4±8.96 kg, 178±6.52 cm, 54.1±4.85 mL·kg-1·min-1 V̇O2max) performed the YYIR1 and underwent a cardiopulmonary exercise test (CPET) on a treadmill in order to assess their ventilatory thresholds (aerobic threshold (AT), respiratory compensation point (RCP), and maximal oxygen consumption (V̇O2max)), buffering capacity, and tolerance to metabolic acidosis. Correlation analyses revealed that the YYIR1 distance was significantly associated with maximal aerobic speed (r=0.542, P=0.006) and V̇O2max (r=0.492, P=0.015), but not with AT or RCP. Position-specific differences were observed in relative acidosis tolerance capacity, with midfielders presenting higher values than defenders (P=0.018, η2=0.294), whereas no significant differences were noted for relative buffering or YYIR1 distance across positions. In conclusion, maximal aerobic speed and V̇O2max were the strongest predictors of YYIR1 performance in professional soccer players, outperforming submaximal thresholds such as AT and RCP. Moreover, positional differences in acidosis tolerance were identified, as midfielders demonstrated greater relative acidosis tolerance capacity compared to defenders.