High-intensity interval training increases mitochondrial biogenesis more rapidly than Zone 2 training due to lactate acting as a signaling molecule.

“the other way it improves metabolic health is these exercise snacks when you're doing a high-intensity you know interval training sort of thing even one or two minutes but mostly when you're going higher than that like 10 minutes 20 minutes uh it's a very potent stimulus to increase the number of mitochondria in your muscle tissue again it's an adaptation you are forcing your muscles to work so hard that they can't use their mitochondria because they again oxygen can't get there fast enough and so they're forced to make energy another way but your muscle is smart it's like oh I need to like adapt so that the next time I'm working hard I can use my mitochondria and the way it adapts is by making new mitochondria it's called mitochondrial biogenesis and high-intensity interval training is one of the best ways to increase mitochondrial biogenesis in skeletal muscle again lactate plays a role in that because lactate is that signaling molecule increases a protein called pgc1 Alpha that regulates mitochondrial biogenesis”