There are a large number of exercise machines on the market today that are not fully ergonomically adapted to exercisers and pose a potential risk of injury. The aim of this paper is to determine the advantages, limitations and disadvantages of the leg extension machine and to offer solutions for better ergonomic symbiosis of the exerciser and the machine. By studying several types of the leg extension machine and doing detailed interviews of users in a nearby gym, conclusions were made that enable the achievement of the desired goal. Deficiency of the device was noticed in experienced and inexperienced exercisers. Inexperienced exercisers do not have enough knowledge to adjust the device to their anthropometry, and experienced ones, although they have enough knowledge, due to the limitedness of the device cannot fully achieve the correct ergonomic position. Based on the observed shortcomings and limitations, it is necessary to enable a more stable position of the pelvis and lower back, prevent the possibility of placing the lever mechanism in an unfavorable position for the knee, allow better adjustment, increase the rigidity of the roller mechanism, improve rope quality and reconstruct the backrest. A more stable position of the pelvis and lower back is achieved by a stabilization belt similar to the one that is used in the seat of passenger aircraft. The lever mechanism is prevented from being placed in undesirable position for the knee by eliminating the groove. Better adjustability can be achieved by increasing the number of slots and reducing their spacing, or by constructing special finely adjustable rotary and translational mechanisms. The stiffness of the roller mechanism can be increased by using a material of higher flexural stiffness or by increasing the cross section of the roller mechanism. Using a better quality rope eliminates the problem of loosening. Finally, by reconstructing the backrest in the shape of the letter "S", greater support for the spine is achieved.