This article analyses methods and approaches for assessing heart rate variability (HRV). One of the approaches is to study the impact of sports, in particular running athletics on HRV. As a result of the research, it was found that sports increase HRV by increasing the sympathetic share. The HRV method is influenced by various factors: diseases, external factors, physiological and lifestyle factors. Those that influence the athletic achievements of athletes are also considered. The impact of stress on HRV can be studied by creating 3D serious games to simulate various stressful situations and to study their impact on HRV. The article presents virtual reality systems, which are of two types: with immersion and without immersion and their application in the study of HRV. It follows from the analysis that the level of sympathetic tone in the analysis of HRV using virtual reality depends on the degree of immersion. Another approach to assessing HRV is to monitor patients at night to determine parasympathetic tone of the autonomic nervous system. For the accurate analysis of HRV, the mathematical methods used are important, which are mainly divided into linear and nonlinear. Spectral analysis is an example of linear, and Poincarè plot is nonlinear.