In this paper, the specificity of the development of muscle definition in recreational athletes will be highlighted, and as it is a group of recreational exercisers, their difference in relation to amateur athletes and professional athletes will be explained. We will also mention anthropometry as a method of measuring the morphological features of the human body, as well as special instruments used to obtain anthropometric data. In the middle of the work, we will mention the main terms that we must understand if we want to create a quality muscular definition of the body. Methods and equations for calculating the energy consumption of basal metabolism, methods of calculating the body's energy consumption throughout the day depending on the person's activity, caloric deficit and surplus, and the body mass index as an indicator of the state of the body from undernourishment to obesity, such terms are therefore explained in detail within the paper. It is necessary to know all this in order to be able to determine the initial state of the recreational exerciser's body, and therefore also in the final state, more precisely after the training process has been completed, so that we can determine whether we have achieved the purpose of that process. Energy sources also fall into the category of important concepts, where I will explain the difference between anaerobic and aerobic exercise. When we talk about weight training and cardio training, we mention the main "weapon" for the fight against subcutaneous fat, so the weekly weight training program and the time when it is most useful to do cardio training will be explained in the examples. Perhaps the last, but not the least important will be the mention of nutrition. In the aforementioned, I will explain the main components of food, their caloric value, the amount and number of meals per day, and nutritional supplements, which is certainly an important link for knowing how to adjust the daily menu for the purpose of developing muscle definition.