When podcaster and physician Peter Attia published his blockbuster longevity book Outlive in 2023, he introduced a previously niche workout concept to a much wider audience. Attia claims that “Zone 2” training, which refers to long and relatively easy bouts of exercise, is crucial to metabolic health – an idea that runs counter to more than a decade of enthusiasm for high-intensity interval training.

Going slow and steady isn’t a new concept, but Attia and other Zone 2 boosters bring a high-tech biohacking ethos to the topic. It’s not just about going for, say, a relaxed bike ride; it’s about maintaining a very specific level of intensity that’s neither too easy nor too hard.