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 (VO2) 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 +/- 3.3y, 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 VO2, 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. DUES, derived from the logarithmic relationship between VO2 and minute ventilation (V-E), was determined at 75% (OUES75), 90% (OUES90) and 100% (OUES100) of exercise duration. After endurance training in T, VO2 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 VO2 at peak- and VAT-levels, OUES75, OUES90 and OUES100 did not significantly change after endurance training. While VO2 and power output at peak- and VAT-levels increased in all T, training-induced changes in ODES appeared more variable. We concluded that DUES was not sufficiently sensitive to highlight improvement of cardiorespiratory reserve after endurance training whereas VO2 at peak and VAT levels did.