Abstract: The present invention discloses a method for monitoring an exercise. The method comprises: building up an energy metabolism system having an energy metabolism feature, wherein the energy metabolism feature comprises a first feature factor, wherein the first feature factor is associated with a first biological system being one of a plurality of biological systems of a human body and not associated with the complete human body; building up a mathematical model describing that an energy expenditure depends on at least one exercise-associated parameter based on the energy metabolism feature for the energy metabolism system; estimating the energy expenditure based on the at least one exercise-associated parameter measured in the exercise by the mathematical model of the energy metabolism system; and monitoring the exercise based on the energy expenditure.