Figure 3. Typical PCr and intracellular pH (pH_i) kinetics as well as the relationship between V_eff and ΔpH during the recovery from 30 s of maximal rate exercise.

The PCr (A) and pH_i (B) kinetics were used to determine PCr utilization rates, buffer capacity, proton efflux rates (V_eff; C), oxidative capacity, and glycolytic flux. PCr and pH recoveries were fitted as a sum of exponentials with amplitudes A₁ and A₂, and rate constants k₁ and k₂. PCr kinetics were fitted as:

where Rest is the fully recovered PCr level and Depl is the initial PCr level. pH kinetics during recovery were fitted as:

where pH_min is the minimum pH obtained during recovery. Following a period of post-exercise acidification, pH_i recovered with an approximate linear rate of 0.13 pH units min⁻¹ and with a rate constant of 0.34 min⁻¹. Based on the V_eff kinetics following the post-exercise acidification period (C) the peak efflux rate was 8.4 mM min⁻¹ and λ was determined to be 13.1 mM (pH unit)⁻¹ min⁻¹.