Introduction : Park fitness machines have been introduced in different countries to facilitate sports movements on the sidewalks and open spaces. The advantages of these devices are ease of use and also performing sports movements with the help of users' weight while exercising on the device. This equipment uses muscles and joints. This performance is the result of design thinking and creativity. It can also be accepted that the installation of fitness equipment is a positive step towards culture building and public participation in public sports. Bodybuilding machines are designed to improve the speed of body movements and increase the speed of contraction. In this regard, the design for multiple stations of equipment causes a variety of resistance training. The devices usually consist of ۱۲ stations, which are for the upper limbs, lower limbs and trunk, which are adapted for bending or opening the joints of the body (Fig. ۱). Resistance by body weight, volume increase, isokinetic device or systems with hinged connections. Methods: In this study, a conventional chest press was studied, imaged and measured. The forces acting on each component were embedded on the free body diagram of the forces (Fig. ۲). Newton equilibrium equations were established for different sections. The relation of hand force in terms of weight and in proportion to the dimensions and geometric positions was obtained as follows. By torque around the highest joint of the device, the relationship between hand force and inclined axis force was calculated, which is shown in Equation ۱. Establishing torque equilibrium around the lower joint determines the relationship between the seat force and the inclined axis force shown in Equation ۲. For the subject sitting on the machine and applying force to the handle, we also balance the forces along the vertical axis to obtain Equation ۳. Then, from the sum of the above three equations, the relation of hand force in terms of weight and in proportion to the dimensions and geometric positions is obtained as follows. Conclusion: In this study, using free graph analysis of geometric connections and the force between the dimensions and sizes of the chest press machine and the force applied from the hands to the device proportional to the body weight of the subject was presented. Based on this, the force entering the machine can be calculated and analyzed at any time according to the angles and geometric dimensions of the chest press machine.