Fig 4. Comparison of different modelling approaches on a short filament.

Shown are the different modelling approaches on a filament with n = 7 RU’s and 18 crossbridges. Results for the ‘brute-force solution’, and the representative state approximation overlap and are indicated by a single line. The Monte Carlo approximation performs well, with only a ∼ 1% difference at higher force levels. Comparison with the independent crossbridge approximation shows the importance of including XB-RU cooperativity, which increases calcium sensitivity, as well as XB-XB cooperativity, which increases maximum force development as shown by the difference in the number of crossbridges bound per half-sarcomere at high calcium. Note that due to the lower number of 7 RU’s, cooperativity is significantly lower than in realistic models with 26 RU’s presented in other results, and the duty ratio is moderately reduced to approximately 2.7/18 = 15%.