Fig. 2. The rise and fall of the calcium transients (green) and the resulting activation level (blue) are shown for the original block model (A) and the twitch model (B). Twitches were applied to the model at a frequency of 22 Hz, the same as in the experimental design, and each individual stimulus (twitch) lasted 7.5 ms. The constants ₁ (0.03), ₂ (0.10), K (0.19) and n (2.8) were optimised to produce fits to respond to a single stimulus condition (Fig. 3). A time constant, (d=0.015 s), was also required to delay the onset of activation, as was seen in the experimental results. This time constant is thought to be due to the time taken for ATP turnover to proceed and for the calcium signalling to cause a calcium influx.