Before revision:  These motors rely on  ATP, supplied at the limits of diffusion from the sarcoplasm to the interior of the lattice of actin and myosin . Classic sliding filament theory suggests that lattice spacing is constant . If so, then the lattice changes volume during contraction and could provide fluid motion and hence assist in transport of molecules between the contractile lattice and  surrounding intracellular space.
After revision:  These motors rely on ATP, supplied at the limits of diffusion from the sarcoplasm to the interior of the lattice of actin and myosin filaments. The radial spacing of filaments in this lattice may change or remain constant during during contraction. If the lattice is isovolumetric, it must expand when the muscle shortens. If, however, the spacing is constant or has a different pattern of axial and radial motion, then the lattice changes volume during contraction and could provide fluid motion and hence assist in transport of molecules between the contractile lattice and surrounding intracellular space.