The oxygen uptake threshold during incremental exercise test

Area of Science:

• Exercise Physiology
• Sports Science
• Human Performance

Background:

• The relationship between oxygen consumption (VO2) and exercise intensity is typically linear during incremental exercise.
• Recent studies suggest a non-linear increase in VO2, termed the oxygen uptake threshold (OUT), using complex methodologies.
• The underlying mechanism of this non-linear VO2 increase requires further investigation.

Purpose of the Study:

• To determine if the oxygen uptake threshold (OUT) can be identified using a simpler method involving two best-fitting lines.
• To test the hypothesis that a non-linear VO2 increase results from continuous oxygen drift during higher intensity exercise.
• To compare the power output at the OUT with the power output at the lactate threshold (LT).

Main Methods:

• Six cyclists performed incremental exercise tests on a cyclo-ergometer.
• The lactate threshold (LT) was determined using the intersection of two best-fitting lines in a log-log plot of lactate concentration versus power.
• The oxygen uptake threshold (OUT) was assessed using a similar two-line fitting method on VO2 data, and the VO2 time course during each exercise step was analyzed.

Main Results:

• The oxygen uptake threshold (OUT) was identified in five out of six subjects.
• The lactate threshold (LT) was identified in all six subjects.
• Power output at OUT (168 ± 13 W) was comparable to that at LT (180 ± 25 W), with observed oxygen drift above both thresholds.

Conclusions:

• The oxygen uptake threshold (OUT) is a discernible phenomenon during incremental exercise.
• A simple two-line method can effectively identify the OUT.
• The OUT is associated with continuous oxygen drift occurring at exercise intensities above the lactate threshold.