Evaluation of Fitness Level by the Oxygen Uptake Efficiency Slope after a Short-Term Intermittent Endurance Training

Several indicators are used as indices of cardiorespiratory reserve. Among them, oxygen uptake (VO ₂ ) at peak and ventilatory threshold (VAT) levels are the most common used. In the present study, endurance training was used to evaluate and compare the usefulness of a new index, the Oxygen Uptake Efficiency Slope (OUES) as an alternative to the previous ones. Fifteen physical education student women participated in the study (8 as a trained group [T: age (mean ± SD) 21.9±3.3 y, height 165.1 :: 5.5 cm, weight 60.4±3.3 kg] and 7 as a control group [C: age 21.7±1.9 y, height 165.4±7.2 cm, weight 59.6±8.6 kg]). Before and after 6 weeks of the Square-Wave Endurance Exercise Test (SWEET) training program or daily activities, they performed an incremental test (30 W/3 min) on a cycle ergometer to determined V̇O ₂ , power output and parameters associated with breathing efficiency (the respiratory equivalents, and the ventilatory dead space to tidal volume ratio [Vd/Vt]) at peak-and VAT-levels. The slope of the relationship between ventilation and carbon dioxide production was also calculated. OUES, derived from the logarithmic relationship between V̇O ₂ and minute ventilation (V̇ _E ), was determined at 75% (OUES75), 90% (OUES90) and 100% (OUES100) of exercise duration. After endurance training in T, V̇O ₂ and power output were significantly improved at peak- and VAT-levels while all breathing efficiency indices remained unchanged. No changes were observed in C after 6 weeks. Despite significant correlation between OUES values and V̇O ₂ at peak- and VAT-levels. OUES75, OUES90 and OUES100 did not significantly change after endurance training. While V̇O ₂ and power output at peak- and VAT-levels increased in all T, training-induced changes in OUES appeared more variable. We concluded that OUES was not sufficiently sensitive to highlight improvement of cardiorespiratory reserve after endurance training whereas V̇O ₂ at peak and VAT levels did.