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High-intensity interval training alternates near-maximal bursts at 80 to 100 percent of maximum heart rate with short recoveries, relying mainly on anaerobic energy, and sessions usually last under 30 minutes. The episode explains how the resulting homeostatic disturbance pushes the aerobic system to adapt, for example by building mitochondria. Sprint interval training goes further, demanding supramaximal effort of 130 to 170 percent of VO2 max. In the 1970s coach Peter Coe had his son Sebastian Coe run repeated 200-meter sprints with 30 seconds of rest, and Sebastian went on to win Olympic gold.

In 1996 Professor Izumi Tabata tested Japanese Olympic speed skaters on braked bikes with 20 seconds of work and 10 seconds of rest at about 170 percent of VO2 max for four minutes. They matched the aerobic gains of a group doing 60-minute sessions five days a week and also gained anaerobic capacity. Later work by Martin Gibala, Jorge Zuniga and Niels Vollaard refined protocols, and a 2017 meta-analysis found six to ten sprints added no aerobic benefit over two. The episode covers benefits for arteries, insulin sensitivity, adolescent obesity, cognition and chronic low back pain, and risks including hyperperfusion and joint sprains.

• Gibala’s Little method uses 60 seconds of work and 75 seconds of rest.
• Zuniga found a 30 seconds on, 30 seconds off rhythm effective, including for Army ROTC cadets.
• Vollaard’s 10-minute routine is mostly easy pedaling with just two 20-second all-out sprints.
• Men facing urological cancer surgery used a month of HIIT as prehabilitation before the operation.
• Rutgers research found high rates of knee, ankle and shoulder sprains, and the American College of Sports Medicine advises consulting a physician first.