Can anyone help simplify HIIT for me?
 

I get the basic 30/30 idea, but I don't think I get how to execute it yet without a more structured enviroment. Doing it on my own makes my brain go duhh. I'm still sick, but it's starting to taper off and I'm feeling well enough to exercise, so I'm getting back on my bike until I can get into some tae bo or something.

I'm using this system I found online:

0-3:59 (Warmup)
4-7:59 (30/30)
8-11:59 (moderate pace)
12-15:59 (30/30)
16:-19:59 (cool down)

but I'm confused, when I'm doing the 30/30, is it enough to just pedal harder, or do I actually need to up the resistance on the bike?