when it comes to HIIT, is it just going fast that counts or does resistance come into it? i use a cross trainer.. i can go f*in fast on it but it doesn't necessarily get me as out of breath compared to if i was to sprint.. i could up the resistance to something very difficult tho and try to go as fast as i can in a higher resistance -cos that would knaker the hell out of me after a minute!

Resistance can certainly come into it.

For example, if going as hard as you can for 30 seconds or 1 minute etc. doesn't come close to getting you winded / feeling ' wiped out '...then simply experiment ( i.e via trial and error ) with bumping your resistance level up till you do.

brilliant, cheers