Sensitivity of V̇O, critical power and V̇O on-kinetics to O concentration/delivery and other factors in skeletal muscle.

Relative sensitivities of the maximal oxygen uptake (V̇O), critical power (CP) and transition time of the primary phase II of the V̇O on-kinetics (t) to selected factors in skeletal muscle are simulated using a computer model of the skeletal muscle bioenergetic system. In normoxia, V̇O is significantly positively sensitive to peak P (P, P at which exercise is terminated because of fatigue), OXPHOS (oxidative phosphorylation) activity (k) and ESA (each-step-activation) intensity (A), and negatively sensitive to the accessible phosphate (and total creatine) pool (P). CP is additionally moderately positively sensitive to critical P (P, P at which the additional ATP usage appears) and negatively sensitive to the additional ATP usage activity (k). t is significantly positively sensitive to P and negatively to k and A. The positive sensitivity of V̇O and CP, and negative sensitivity of t to O concentration/delivery is low at normoxic and hyperoxic O levels, but increases significantly at severely hypoxic O levels.