Originally Posted by DaveMCMkIII

high repitions (12+ reps) 30-60 secs

med reps (10-12) 2-3mins

low reps (6-8) 3mins

higher reps ush require short rests so to maintain a good,high intensity (heart rate), as this is the aim of such a session. Low reps require good rests so you can recover well and recruit your muscles around maximal again, which exposes muscles to greater forces.