Fig. 5.

Model verification: comparison of model simulations and independent data for other stimulation frequencies than used for parameterization. Model simulations according to configurations i, ii, and iii are indicated in red, green and blue, respectively. Experimental data are indicated in black and correspond to muscle stimulation protocols of 1 Hz continues stimulation (A and C) and 40 Hz (1 pulse train per 5 s, 20 pulses per pulse train; B and D). Error bars indicate SE (n = 4–5). E and F: predictions according to model configuration iii (solid lines) of ATP supply flux by PCr hydrolysis (grey lines) and glycolysis (black lines) and ATP demand flux (blue lines), compared with values derived from the experimental data by using the phenomenological model (dots) described by Conley et al. (9). Calculations with the phenomenological model were performed using the estimated value of the static proton buffer capacity as listed in Table 3. As a result of the fast (de)activation kinetics of PFK-1 (see Fig. 7) the net glycolytic ATP synthesis flux was also pulsatile. For clarity of presentation, the glycolytic flux (black lines) indicated represents the net flux averaged over epochs of 5 s.