Oxygen uptake efficiency slope in healthy normal weight young males: an applicable framework for calculation and interpretation

Background: The oxygen uptake efficiency slope (OUES) is considered a reliable indicator of cardiorespiratory fitness (CRF) in young and clinical populations who cannot achieve maximal effort during a graded exercise test. However, OUES accuracy depends on the data points used for its calculation and it is still not clear if the submaximal OUES can accurately assess CRF in healthy young males. Objective. We investigated the association between peak oxygen uptake (VO2peak) and peak and submaximal OUES, and the agreement between submaximal OUES and peak OUES in male adolescents and young adults. Methods. Fifty normal weight healthy participants (age 14-22 years, VO2peak 43.8 ± 7.3 mL·min-1·kg1) performed a graded exercise test on a cycle ergometer, pulmonary gas exchange was assessed using breath-by-breath analysis. VO2peak, and oxygen consumption (VO2) at the aerobic (AerT) and at the anaerobic threshold (AnT) were determined as the 30-second average of the VO2 values. Peak OUES (up to peak) and submaximal OUES (up to AerT and up to AnT) were calculated from the logarithmic relation between VO2 and pulmonary ventilation. Results. VO2peak showed higher correlations with peak OUES (r=0.80-0.88) than with the two submaximal OUES (r=0.32-0.81). Peak OUES showed higher agreement with OUES up to AnT (r=0.89-0.93; Typical percentage error 5.9%; Intraclass correlation coefficient = 0.89-0.93) than with OUES up to AerT (r=0.39-0.56; Typical percentage error 15.0%; Intraclass correlation coefficient = 0.38-0.56). Conclusions. The peak OUES is the best indicator of aerobic fitness in healthy males followed by the OUES up to AnT. The OUES up to AnT is a valid alternative to peak OUES.