I found this HIIT routine last night while researching and got inspired to try it. There's some science behind it. The first section depletes something, the second section depletes something else and the third section depletes it all better. Sorry, I don't recall.
I've been running pretty intense intervals, so I was surprised my body feels as "spent" as it does. It was not overly difficult in the moment, I think because I'm pretty conditioned for this type of training already.
2:00- warmup/walk
8:00- 15 sec. all out sprint/ 45 sec jog
25:00- steady-state jog or run
10:00- 1:00 sprint (but not all out)/ 1:00 jog
The time went by pretty quickly and overall it was a great workout. My calves are really feeling it, probably from the all out sprints which I did on a hard gym floor.