V̇O₂ (non-)linear increase in ramp-incremental exercise vs. V̇O₂ slow component in constant-power exercise:...

Area of Science:

• Exercise Physiology
• Skeletal Muscle Bioenergetics
• Computational Modeling

Background:

• Muscle fatigue is often linked to the P_i double-threshold mechanism.
• Understanding oxygen uptake (V̇O₂) kinetics during exercise is crucial for assessing muscle function.
• Differences in V̇O₂ response between ramp-incremental and constant-power exercise remain a key area of investigation.

Purpose of the Study:

• To investigate the V̇O₂ (non-)linear increase during ramp-incremental exercise compared to the V̇O₂ slow component during constant-power exercise.
• To analyze the role of the P_i double-threshold mechanism in both exercise protocols.
• To elucidate the factors contributing to the differing V̇O₂ kinetics between exercise types.

Main Methods:

• Development and application of a computer model of the skeletal muscle bioenergetic system.
• Simulation of the P_i double-threshold mechanism under both ramp-incremental and constant-power exercise conditions.
• Analysis of adenosine triphosphate (ATP) usage and anaerobic glycolysis contributions.

Main Results:

• The P_i double-threshold mechanism is applicable to both exercise protocols.
• Additional ATP usage initiates at a higher power output in ramp-incremental exercise compared to constant-power exercise.
• Lowered additional ATP usage or elevated glycolysis in ramp exercise explains the reduced V̇O₂ non-linearity.

Conclusions:

• The V̇O₂ (non-)linearity in ramp exercise and V̇O₂ slow component in constant-power exercise are influenced by the balance between ATP demand and anaerobic glycolysis.
• Exercise intensity and protocol type significantly modulate the bioenergetic response and fatigue mechanisms.
• The P_i double-threshold model provides a framework for understanding exercise V̇O₂ kinetics and muscle fatigue.