In HIIT, high-intensity is followed by “interval” before “training.” HIIT stands for high-intensity interval training, a workout method that alternates brief bursts of very hard exercise with recovery periods.
The defining feature is the repeated interval structure, not simply exercising hard. A session may alternate sprinting with walking, cycling with easy pedaling, or intense bodyweight movements with rest. The length and intensity of the work and recovery periods vary according to the program and the participant’s fitness.
The method has several notable historical strands. In the 1970s, athletics coach Peter Coe used repeated fast 200-meter runs with short recoveries. A 1996 study by Izumi Tabata and colleagues later popularized the 20-seconds-work, 10-seconds-rest format now widely called Tabata training.
A common mix-up is treating HIIT and Tabata as exact synonyms. Tabata is one specific HIIT-style protocol, while HIIT is the broader category. Sprint interval training is related but generally uses all-out, supramaximal efforts.