High-intensity interval training (HIIT) is an exercise plan where participants work out very intensely for a brief period before taking a break and then repeating the process. In this video, nutrition and fitness expert Janet Bond Brill, PhD, RDN, FAND, LDN, cautions that while HIIT has many cardiovascular benefits, it may be too challenging for many out-of-shape Americans. As such, Dr. Bond Brill suggests that these people should focus on basic cardiovascular activities (such as walking) and other lifestyle interventions, such as adopting a healthier diet, instead of focusing solely on HIIT. People who engage in HIIT should do so several times a week, taking care to also practice weight and flexibility training on the remaining days.