Objective. HIIT corresponds to the English acronym of High Intensity Interval Training, which in Spanish means Training in High Intensity Intervals, a name that already gives us an idea of the subject and focus that this activity will have.It consists of performing exercises that usually involve the work of a large number of muscle groups, so that intervals of great intensity are alternated with intervals of medium and low intensity. Following this dynamic, it is possible that a complete recovery between the high intensity intervals will not occur.The exercises to be performed are very varied, including activities such as running or cycling, and also "static" exercises such as squats, jumps, pull-ups, push-ups.The aim of this investigation was to explore the effect of high intensity interval training (HIIT) on weight, body mass index and body fat percentage for adults. Methods. Forty (20) physical fitness practitioners did not have any training experiences that were randomly. The researchers took written approval from the participants. Results:The results showed statistically significant differences between the pre-and post-test for weight, BMI and BFP. Conclusion. In conclusion, we have demonstrated that HIIT conveys benefits to weight loss may be superior to the effect of traditional continuous training. HIIT may therefore be suitable as an alternative to continuous exercise training in the promotion of health and weight loss, more research is needed to determine both behavioral responses and clinical benefits over the longer term. Keywords: HIIT, Body Mass Index, Body Fat Percentage.