First of all I don’t do cardio for over 20 minutes.

As for HIIT I warm up for 50 minutes then hit it.
30 sec all out sprint then 30 second coast
do this for 5 minutes and you are done.
Next time repeat, 3rd time up it to six minutes for 2 session and then 7 and so on. It’s all you need. IMO

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The Fool say in his heart "There is no God"