Background/Objectives: The practice of physical activity contributes to obtaining adequate values of body composition and physical fitness, which is beneficial for people’s health. However, a large part of the adult population does not comply with the recommendations for physical activity, due to factors such as lack of time and nearby sports venues. Immersive virtual reality is a tool that allows individuals to immerse themselves in a simulated world and perceive visual, auditory, and tactile sensations. Its use in physical activity interventions favors exercise in situations that, due to time and space, could be limited in real life. The objective of this case report is to measure the impact on body composition and physical fitness of an exercise program executed through immersive virtual reality. Methods: The design is a case study with a quantitative approach developed through a physical activity intervention with immersive virtual reality in which body composition was evaluated considering fat and muscle components, and physical fitness considering cardiorespiratory fitness, speed-agility, and hand grip strength, through pre- and post-testing. The physical exercise program based on immersive virtual reality lasted 8 weeks. The subject of the study was a 24-year-old man, a second-year student of Pedagogy in Physical Education at a Chilean university, with no previous experience in this virtual tool. Results: The results indicate that for body composition the study subject decreased the fat component and slightly improved the musculature, while for physical fitness cardiorespiratory fitness and speed-agility improved, but manual grip strength decreased. Conclusions: It is concluded that the training developed through immersive virtual reality proves to be a tool that can promote improvements in body composition and physical fitness; it is necessary to carry out more research to validate the potential of this instrument as a means of contributing to the health of the population.