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

A computer model of the skeletal muscle bioenergetic system involving the P double-threshold mechanism of muscle fatigue was used to study the V̇O (non-)linear increase in time in ramp-incremental exercise as compared to the V̇O slow component in constant-power exercise. The P 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) V̇O non-linearity in ramp-incremental exercise, than V̇O slow component in constant-power exercise. The V̇O (non-)linearity in ramp-incremental exercise and V̇O slow component in constant-power exercise is a derivative of a balance between the additional ATP usage and ATP production by anaerobic glycolysis.