A number of methods can be found in the literature to gravity balance a machine. In this paper we use hybrid method to achieve gravity balancing. Hybrid method employs a mechanism to locate center of mass of the robot in conjunction with springs. This method is used to develop a rehabilitation device, which compensates the effect of gravity on a human leg. For a quantitative evaluation of the performance of the device, electromyograph data of the muscles involved in the motion of leg were collected and analyzed. This data showed that the machine could be used for gravity balancing of the leg and could be potentially used for rehabilitation of patients.