Biochemical origin of (near-) linear curvature constant (W')- slow component ( ) and critical power (CP)- ...

The biochemical background of the (near-)linear direct relationship between the curvature constant (W') of the power-duration curve and the magnitude ( $$ ) of the slow component of the $$ on-kinetics ( $$ ) as well as reverse relationship between critical power (CP) and the characteristic transition time (t_0.63, analogous to τ_p) of the primary phase II of the $$ on-kinetics encountered in experimental studies is studied.

A computer model of the bioenergetic system in skeletal muscle, involving the each-step-activation mechanism of work transitions and P_i double-threshold mechanism of muscle fatigue, is used.

The activity (rate constant) (k_add) of the additional ATP usage, underlying the slow component, determines to a large extent the (near-)linear direct W'- $$ relationship, as an increase in k_add increases markedly both W' and $$ . t_0.63 is a derivative of the changes in metabolite (M = PCr or Cr or P_i) concentrations between rest and the steady-state of the phase II M on-kinetics after the onset of exercise. The oxidative phosphorylation (OXPHOS) activity (k_OX) mostly determines the (near)-linear inverse CP-t_0.63 relationship, as an increase in k_OX markedly decreases ΔM and t_0.63, and elevates CP.

The $$ on-kinetics (e.g., $$ or t_0.63) cannot cause anything in the system, as it is an emergent property of the system functioning on the biochemical level. Physiological variables: muscle $$ and W' as well as t_0.63 and CP, and relationships between them, are determined by biochemical parameters, mainly k_add and k_OX, respectively.