Table 2.

Symbols and meaning for occurring model parameters

Part	Symbol	Unit	Initial guess value	Source	Meaning
Actin filament	${\ell }_{\text{act}}$	[μm]	1.1	(91)	length of actin (half) filament
	ract	[nm]	5.5	(92)	radius of actin filament
	${\varrho }_{\text{act}}$	[nm]	5.5	(91)	repetition of active sites
	${\varrho }_{\text{TnC}}$	[nm]	37.5	(91)	repetition of TnC terminals
	nTnC	[ ]	$4\cdot {\ell }_{\text{act}}/{\varrho }_{\text{TnC}}=117$	–	number of TnC terminals per half-sarcomere primitive (two actin filaments and two tropomyosin helices)
	nact	[ ]	7 ⋅ nTnC≈820	–	number of active sites per half-sarcomere primitive
Myosin filament	${\ell }_{\text{mbb}}$	[μm]	0.8	(91)	length of half-myosin filament (backbone)
	${\ell }_{\text{mbz}}$	[μm]	$0.1\cdot {\ell }_{\text{mbb}}=0.08$	(91)	half-myosin bare zone width
	rmbb	[nm]	7.5	(19)	inner myosin backbone (rod) radius
	$R_{{\mathcal{Z}}_{\text{S}1}}$	[nm]	13	(60)	charge location on myosin head
	${\varrho }_{\text{S}1}$	[nm]	14.3	(91)	repetition of myosin crowns (each three double-heads)
	nS1	[ ]	$3\cdot \left({\ell }_{\text{mbb}}-{\ell }_{\text{mbz}}\right)/{\varrho }_{\text{S}1}\approx 150$	–	number of myosin double-heads per half-sarcomere
	χact,mbb	[ ]	2:1	–	ratio actin to myosin filaments
	ncb,max	[ ]	$1/\varsigma \cdot n_M\approx 100$	(93,94)	maximum number of possible cross-bridges
	ς	[ ]	1.8	(93,94)	reciprocal of ratio of maximally formed cross-bridges
	${\tilde{F}}_{\text{false}}$	[ ]	0.1	(95), Table 1	ratio of force between false and proper cross-bridges
Hill equation	$\tilde{c}$	[ ]	state [0 … 1]	–	relative concentration of calcium ions
	ν	[ ]	2.5	(96)	Hill exponent
	$K_{\tilde{c}}$	[ ]	1/40	(96)	Hill coefficient
Half-sarcomere geometry (all values here for hexagonal lattice)	${\ell }_{\text{hs}}$	[μm]	state [0.4 … 2.2]	–	half-sarcomere length
	${\ell }_{\text{hs},\text{ref}}$	[μm]	${\ell }_{\text{act}}=1.1$	–	half-sarcomere reference length
	κ10	[ ]	$2/\sqrt{3}$	–	lattice constant
	$d_{10}\left({\ell }_{\text{hs}}\right)$	[nm]	$2/3\cdot \sqrt{d_{10,\text{ref}}^2\cdot {\ell }_{\text{hs},\text{ref}}/{\ell }_{\text{hs}}}$	(50)	lattice spacing as function of ${\ell }_{\text{hs}}$
	d10,ref	[nm]	37	(51), Table 1	lattice spacing at ${\ell }_{\text{hs},\text{ref}}$
	$d_{\text{act},\text{act}}\left({\ell }_{\text{hs}}\right)$	[nm]	$\frac{2}{3}\cdot d_{10}\left({\ell }_{\text{hs}}\right)$	–	(center) distance actin-to-actin filament
	$d_{\text{act},\text{mbb}}\left({\ell }_{\text{hs}}\right)$	[nm]	$d_{\text{act},\text{act}}\left({\ell }_{\text{hs}}\right)$	–	(center) distance actin-to-myosin backbone
	$d_{\text{mbb},\text{mbb}}\left({\ell }_{\text{hs}}\right)$	[nm]	${\kappa }_{10}\cdot d_{10}\left({\ell }_{\text{hs}}\right)$	–	(center) distance myosin-to-myosin backbone
	${\hat{d}}_{\text{act},\text{mbb}}\left({\ell }_{\text{hs}}\right)$	[nm]	$d_{\text{act},\text{mbb}}\left({\ell }_{\text{hs}}\right)-r_{\text{act}}-r_{\text{mbb}}$	–	surface distance actin-to-myosin backbone
	CSAhsp$\left({\ell }_{\text{hs}}\right)$	[μm2]	$d_{\text{mbb},\text{mbb}}\left({\ell }_{\text{hs}}\right)\cdot d_{10}\left({\ell }_{\text{hs}}\right)$	–	cross-sectional area of half-sarcomere primitive
	CSAhsp,ref	[μm2]	${\kappa }_{10}\cdot d_{10,\text{ref}}^2=1.6\cdot {10}^{-3}$	–	reference cross-sectional area of half-sarcomere primitive
	$V_{\text{hsp}}\left({\ell }_{\text{hs}}\right)$	[μm3]	$\text{CS}{\text{A}}_{\text{sp}}\left({\ell }_{\text{hs}}\right)\cdot {\ell }_{\text{hs}}=V_{\text{hsp},\text{ref}}$	–	constant half-sarcomere primitive volume
	Vhsp,ref	[μm3]	${\text{CSA}}_{\text{sp},\text{ref}}\cdot {\ell }_{\text{hs},\text{ref}}=1.7\cdot {10}^{-3}$	–	half-sarcomere primitive reference volume
Electrostatics, Debye-Hückel theory	T	[K]	280 … 310	–	temperature of 7 … 37°C
	kB	[N ⋅ m ⋅ K−1]	1.381 ⋅ 10−23	–	Boltzmann constant
	e0	[C]	1.602 ⋅ 10−19		elementary charge
	${\mathcal{Z}}_i$	[ ]	integer	–	charge number (valence) of ion i
	${\mathcal{Z}}_{\text{act}},{\mathcal{Z}}_{\text{mbb}},{\mathcal{Z}}_{\text{S}1}$	[ ]	integer	–	charges on actin/myosin backbone and the head (S1)
	qi	[C]	$\left|{\mathcal{Z}}_i\right|\cdot e_0$	–	absolute electric charge of ion i
	ci	[mol/L]	solution-dependent	–	molar concentration of ion i
	I	[mol/L]	$\frac{1}{2}\sum _{i=1}^n{c}_i\cdot {\mathcal{Z}}_i^2\approx 0.17$	(97)	ionic strength of a solution with n sorts of ions
	NA	[mol−1]	6.02214 ⋅ 1023	–	Avogadro constant
	λ	[nm]	$\sqrt{\frac{{ϵ}_0\cdot {ϵ}_r\cdot k_B\cdot T}{2\cdot {10}^3\cdot N_A\cdot e_0^2\cdot I}}$	(19,98)	Debye length in electrolyte solution
	ϵ0	[C2 · N−1 · m−2]	8.854 ⋅ 10−12	–	vacuum permittivity
	ϵr	[ ]	≈80 for water	(99)	dielectric constant (relative permittivity) of the solvent
	K0(x),K1(x)	[ ]	function	–	modified Bessel functions of second kind
	${\text{Φ}}_{DH\text{cyl}}\left(d\right)$	[J]	$-\frac{q_i\cdot q_j\cdot \lambda \cdot K_0\left(d/\lambda \right)}{2\cdot \pi \cdot R_c\cdot {\ell }_c\cdot {ϵ}_0\cdot {ϵ}_r\cdot K_1\left(R_c/\lambda \right)}$	(100,101)	Debye-Hückel potential energy of cylindrical ion i of radius Rc and length ${\ell }_c$, attracting charge qj
	FDHcyl(d)	[N]	$\frac{q_i\cdot q_j\cdot K_1\left(d/\lambda \right)}{2\cdot \pi \cdot R_c\cdot {\ell }_c\cdot {ϵ}_0\cdot {ϵ}_r\cdot K_1\left(R_c/\lambda \right)}$	–	Debye-Hückel force of cylindrical ions

Which of these are optimizer-fitted parameters is given in Table 3. Activation $\tilde{c}$ and half-sarcomere length ${\ell }_{\text{hs}}$ are state variables. T was set to the temperature at which the experiment was performed. The other entries are either physical constants or auxiliary values/functions.