This paper aims to better understand how Virtual reality (VR) is influencing on human behavior with using biomechanical analysis methods and its application for assembly/disassembly operations simulation in particular. For this purpose, a new haptic model for mechanical energy expenditure is proposed where the required mechanical work is used as main parameter. Then, the fatigue levels are evaluated by analyzing the recorded electromyography (EMG) signal on the four involved muscles of operator's arm. The proposed method is validated by a set of experimental disassembly tests performed in a VR environment. The comparison of the analytical and experimental results has shown good correlation between them. The proposed method provides the feasibility to integrate human muscle fatigue into disassembly sequence evaluation via mechanical energy expenditure when performing disassembly operation simulations in the initial stage of product design.