This study deals with the development of a mathematical model for the musculo-skeletal system capable of evaluating muscle forces and joint reactions for different static postures. The problem is formulated as a linear program and solved by means of a simplex algorithm. Different criteria are used for evaluation of the muscle forces necessary to maintain the human body equilibrium in standing, leaning and stooping. The analytical results show good correlation with electromyographic signals from surface electrodes placed on the superficial muscles. The feasibility of this approach for quantitative analysis of musculoskeletal forces is demonstrated. The technique represents the first attempt at a mathematical model of the musculo-skeletal system and can be readily extended for complete simulation of the force system controlling human body actions and motions. It provides a valuable tool for diagnosis of muscle malfunctions, changes in musculoskeletal forces resulting from injury and synthesis of assistive devices for rehabilitation.