This episode takes a long look at the mechanisms behind aerobic adaptations from high intensity exercise, starting with an early study showing how AMPK activation leads directly to mitochondrial biogenesis, followed by a recent meta-analysis showing when high intensity exercise does and doesn't lead to adaptation. We provide guidelines in terms of exercise intensity, duration, and how well trained you are. Then we give some practical takeaways, plus debunk all the ways "hacking" this adaptive signal chain don't work. Marinus Petersen of KiloWatt Coaching steps in as a guest co-host for Kyle and provides an additional perspective from his coaching experience, and his formal exercise physiology education.