Hello, I am just trying to remember the explanation behind the idea where fat is burned after 20 minutes of cardio.
As far as I can remember it takes about 20 mins to use up glycogen stores, then your body starts getting calories from fat.
However I am unsure as to why you are recommended to run 20-40 minutes in a session and not more.
If it was 20 then you would only be getting into the fat burning zone.
I have an idea that your body stays in the zone when you stop.
Is it bad to do cardio for more than 40 mins because of muscle breakdown?
can someone fill me in.