Oxygen uptake kinetics during incremental- and decremental-ramp cycle ergometry

Area of Science:

• Exercise Physiology
• Cardiopulmonary Function
• Human Performance

Background:

• Pulmonary oxygen uptake (VO2) kinetics during incremental exercise typically follow first-order kinetics.
• A VO2 slow component, or excess VO2, is generally not observed above the lactate threshold (θL) during incremental ramps.
• The response dynamics of VO2 during decremental exercise ramps are less understood.

Purpose of the Study:

• To investigate if a step-decremental ramp exercise protocol elicits different VO2 response dynamics compared to an incremental ramp.
• To determine if the VO2-work rate (WR) relationship differs between incremental and decremental ramp protocols.
• To examine the kinetics of VO2 response in the supra-θL domain during incremental and decremental ramps.

Main Methods:

• Ten healthy males performed maximal incremental ramp cycle ergometry (15-30 W·min⁻¹).
• Subjects also completed a step-decremental ramp protocol, increasing WR to maximum then decreasing at the same rate.
• Five subjects performed a sub-maximal decremental ramp test starting at 90% of θL. VO2 was measured breath-by-breath.

Main Results:

• The VO2-WR slope for the incremental ramp was 10.3 ± 0.7 ml·min⁻¹·W⁻¹.
• The VO2-WR slope for the descending limb of the decremental ramp was significantly steeper at 14.2 ± 1.1 ml·min⁻¹·W⁻¹ (p < 0.005).
• The sub-maximal decremental ramp slope (9.8 ± 0.9 ml·min⁻¹·W⁻¹) was not significantly different from the incremental ramp slope.

Conclusions:

• The steeper VO2-WR slope during the supra-θL domain of the decremental ramp suggests altered response dynamics compared to incremental ramps.
• The findings indicate that the VO2 response during incremental ramps above θL may represent pseudo, rather than actual, first-order kinetics.
• The underlying physiological mechanisms responsible for the differing kinetic responses between incremental and decremental ramps require further investigation.