Oxygen uptake kinetics during treadmill running across exercise intensity domains

Area of Science:

• Exercise Physiology
• Human Physiology
• Sports Science

Background:

• Understanding oxygen uptake (VO2) kinetics is crucial for characterizing exercise intensity domains.
• The relationship between VO2 response and exercise intensity, particularly across moderate, heavy, and severe domains, requires comprehensive investigation.

Purpose of the Study:

• To comprehensively examine the kinetics of oxygen uptake (VO2) during treadmill running across moderate, heavy, and severe exercise intensity domains.
• To investigate how the amplitude, gain, and time constant of the VO2 primary component change with increasing exercise intensity.
• To analyze the characteristics of the VO2 slow component and its relationship with maximal oxygen uptake (VOmax) at different intensities.

Main Methods:

• Nine subjects performed "square-wave" rest-to-exercise transitions on a treadmill at various intensities.
• Exercise intensities included 80% and 100% of VO2 at lactate threshold (LT) and 20-100% of the delta between LT and VO2max.
• VO2 response was modeled using non-linear regression, and critical velocity (CV) was determined.

Main Results:

• The amplitude of the VO2 primary component increased significantly with exercise intensity.
• A non-significant trend for a decreasing "gain" of the primary component was observed as intensity increased.
• The VO2 slow component increased with intensity up to 80% delta but decreased at 100% delta, with end-exercise VO2 reaching VOmax.

Conclusions:

• The "gain" of the VO2 primary component is not constant across moderate, heavy, and severe treadmill running intensities.
• Intensity-dependent changes in VO2 response kinetics may reflect alterations in muscle fiber recruitment patterns.
• These findings enhance our understanding of physiological responses to varying exercise loads.