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 .
After revision:  These motors rely on energy derived from 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 .