Oxygen uptake efficiency slope at different exercise intensities

Maximal oxygen uptake (VO2max) is considered the gold standard for reporting exercise capacity; however, by definition it requires a maximal effort of subjects. Therefore, the application of VO2 max testing is somewhat limited, and is less reliable when applied to the evaluation of several populations including older adults or subjects with various disease states. The Oxygen Uptake Efficiency Slope (OUES) reflects the relationship between oxygen uptake (in ml/min) and the logarithm of total ventilation (in L/min). Recently, Hollenberg & Tager (2000) demonstrated that the OUES is an objective index of VO2max that does not require a maximal exercise effort. PURPOSE: To clarify the relative intensity that an incremental sub-maximal exercise test must reach in order to obtain a valid and reliable OUES for the purpose of predicting VO2max. METHODS: 15 subjects (10 men and 5 women), healthy, moderately active, mean age 25.3 (range 21 – 37), BMI= 23.9±3.2kg/m2 performed an incremental maximal cycle-ergometry (3’ of unloaded pedaling followed by increases of 30W x 1’). Breath by breath ventilatory expired gas analysis were performed during the tests and VO2 max measured. The OUES was derived by truncating data at various intensities of VO2max (from 50% to 100%). Results are expressed as mean±SD. RESULTS: Mean VO2max was 2903.4 ±944.7 ml/min. The OUES calculated at different intensities of exercise strongly correlated with VO2 max (100% r=.983; 50% r=.900). The regression line of the VO2 max plotted versus the OUES showed a small progressive percent increase of variations. In particular, the OUES at 65% of VO2 max only differed of 6.7% from the OUES at 100% VO2 max. CONCLUSIONS: Our data suggest that the OUES calculated on exercises performed at intensities higher than 65% of VO2 max, appears to be a reliable index of cardiovascular function in young healthy subjects. A higher number of subjects will allow us to develop more reliable equations to estimate the VO2 max from the OUES.