In living cells, molecular motors convert chemical energy into mechanical
work. Its thermodynamic energy efficiency, i.e. the ratio of output mechanical
work to input chemical energy, is usually high. However, using two-state
models, we found the motion of molecular motors is loosely coupled to the
chemical cycle. Only part of the input energy can be converted into mechanical
work. Others is dissipated into environment during substeps without
contributions to the macro scale unidirectional movement