There's also value in spending some time in zone 5 [1]: this is where the heart is really trained as a muscle, and where the cardiovascular system is pushed to its limit (the famous vo2max: increasing vo2max is done in zone 5, for ex. with HIIT [2]).
Zone 2 is all about giving the mitochondries a chance to get better at providing a steady energy flow over a long time, mainly by optimizing for burning fat as fuel instead of glucose, avoiding lactate accumulation during the process [3].
In between, in zones 3 & 4, you get a little of both those ends of the spectrum, it's still helpful to a degree, but it's not really optimized: that why it's deemed preferable to spend the bulk of your training time in either your zone 2 or zone 5.
The ideal composition of a training period seems like 90% zone 2 and 10% zone 5, and going for more than 1h of zone 5 per week seems not that interesting. Also, mixing zone 2 and zone 5 in the same training session is not ideal, it's better to stay focused on one thing at at time.
[1] https://peterattiamd.com/category/exercise/high-intensity-zo...
[2] https://peterattiamd.com/category/exercise/vo2-max/
[3] https://peterattiamd.com/category/exercise/aerobic-zone-2-tr...
Zone 2 is all about giving the mitochondries a chance to get better at providing a steady energy flow over a long time, mainly by optimizing for burning fat as fuel instead of glucose, avoiding lactate accumulation during the process [3].
In between, in zones 3 & 4, you get a little of both those ends of the spectrum, it's still helpful to a degree, but it's not really optimized: that why it's deemed preferable to spend the bulk of your training time in either your zone 2 or zone 5.
The ideal composition of a training period seems like 90% zone 2 and 10% zone 5, and going for more than 1h of zone 5 per week seems not that interesting. Also, mixing zone 2 and zone 5 in the same training session is not ideal, it's better to stay focused on one thing at at time.
[1] https://peterattiamd.com/category/exercise/high-intensity-zo...
[2] https://peterattiamd.com/category/exercise/vo2-max/
[3] https://peterattiamd.com/category/exercise/aerobic-zone-2-tr...