If the 1970s was the decade of jogging and Jazzercise, the 1980s was the decade of aerobics and leotards, the 1990s was the time we all tried Tae Bo, and the 2000s was the decade in which spinning and Zumba classes went mainstream, it’s safe to say that the 2010s represented the golden age of not only CrossFit but also high-intensity interval training (HIIT), or “really short workouts.”