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

• Published in: Respiratory physiology & neurobiology 2023-05, Vol.311, p.104023-104023, Article 104023
• Main Author: Korzeniewski, Bernard
• Format: Article
• Language: English
• Subjects: Constant-power exercise; Muscle fatigue; Oxygen uptake kinetics; Power output; Ramp-incremental exercise; Skeletal muscle
• ISSN: 1569-9048; 1878-1519
• DOI: 10.1016/j.resp.2023.104023

A computer model of the skeletal muscle bioenergetic system involving the Pi double-threshold mechanism of muscle fatigue was used to study the V̇O2 (non-)linear increase in time in ramp-incremental exercise as compared to the V̇O2 slow component in constant-power exercise. The Pi double-threshold mechanism applies to both constant-power and ramp-incremental exercise. The additional ATP usage is initiated at a significantly higher ATP usage activity (power output), determining the moderate/heavy exercise border, in ramp-incremental, than in constant-power exercise. A significantly lowered additional ATP usage activity or elevated glycolysis stimulation at the highest power outputs in ramp-incremental exercise in relation to constant-power exercise can additionally explain the much smaller (or zero) V̇O2 non-linearity in ramp-incremental exercise, than V̇O2 slow component in constant-power exercise. The V̇O2 (non-)linearity in ramp-incremental exercise and V̇O2 slow component in constant-power exercise is a derivative of a balance between the additional ATP usage and ATP production by anaerobic glycolysis. •V̇O2 non-linearity is greater in constant-power (CPE) than ramp exercise (RE).•Computer model involving “Pi double-threshold” mechanism of muscle fatigue is used.•Additional ATP usage and anaerobic-glycolytic ATP supply fix this non-linearity.•Moderate/heavy exercise border is higher in RE, as Pi vs. work increase is delayed.•Additional ATP usage is less and/or glycolysis activation is higher in RE than CPE.