High-Intensity Interval Training: Methodological Considerations for Interpreting Results and Conducting Research

In recent years, high-intensity interval training (HIIT) has gained prominence in the health and fitness area, becoming a worldwide trend. Given the positive results of HIIT, researchers have compared it with moderate-intensity continuous training (MICT). However, much of that research has presented methodological challenges. Therefore, the aim of this opinion article is to address an important risk of bias common in research comparing HIIT and MICT: the lack of equalisation among protocols. This limitation can be considered a risk of bias that limits the conclusions of many studies. Thus, it is necessary to achieve the equalisation of sessions in some way such as using equalisation by energy expenditure, by workload performed in the session, or by duration of the session. High-intensity interval training (HIIT) is a dynamic and complex exercise model that has gained popularity in recent years and become a fitness trend. As a consequence, the number of publications addressing HIIT has also increased significantly.The HIIT model has been shown to be effective for improving different health-related parameters, as well as effective for improving parameters related to sports performance.Caution is needed when comparing HIIT and moderate-intensity interval training (MICT), as many of the studies where these comparisons were conducted do not present any model of equalisation between the protocols.Equalization between protocols (HIIT and MICT) is complex and may have limitations. Thus, the equalization method should be used considering the main objective of the research.