Man of Honour
I understand all that, just didn't get what the difference in running up a hill and doing it on a bike or something would make
Ah right. Well running up hill puts less stress on the knees - and you need a shorter distance to get the same effort requirements!
Spin bike is good for it too actually.
However, I'd rather not go to the gym for HIIT when you can do it at home Also, it's good to vary the movements, like all exercises.