V ˙ O₂ linear-onset kinetics spanning steady- and non-steady-state exercise

Area of Science:

• Exercise Physiology
• Cardiorespiratory Fitness

Background:

• The traditional mono-exponential function for quantifying oxygen uptake (V̇O₂) kinetics during exercise transitions has limitations.
• Anomalies suggest the initial phase (approximately 1 minute) of the V̇O₂ response is linear, not exponential.

Purpose of the Study:

• To compare the accuracy of a linear fit versus a mono-exponential function for initial V̇O₂ kinetics.
• To investigate V̇O₂ kinetics during incremental and constant load exercise in highly endurance-trained individuals.

Main Methods:

• Fourteen highly endurance-trained subjects completed ramp incremental cycling and constant load trials.
• The initial segment of the V̇O₂ response was analyzed using both linear and mono-exponential models.

Main Results:

• The linear fit was significantly more accurate (p < 0.001) than the mono-exponential fit for the initial exercise phase.
• Two distinct profiles of linear onset V̇O₂ kinetics were observed: sustained increase (n=7) and plateau/decrease (n=7).
• Both sub-groups exhibited similar cardio-respiratory and muscular endurance.

Conclusions:

• The linear onset (LO) V̇O₂ kinetics method is a more valid and sensitive approach than the traditional mono-exponential method.
• LO kinetics requires less exercise time, is applicable to various exercise intensities, and reveals more complex physiological patterns.
• Further research is needed to refine LO V̇O₂ kinetics measurement and understand its physiological determinants.