Those are guidlines. You don't start tapping into muscular endurance until you get to 15 or more reps then your tapping into another energy system.
of course they arent set in stone minimum and maximums's. 1-5, 1-6, 1-4.... 5-10, 6-9, 5-11, 4-9, 4-10, 4-11,.... exactly...they could be a little different...but those are for the most part accurate. one thing is for sure if you doing 10-12 your on the high side of the the fast twitch 2B fibers, and where you want to be is in the middle or in the lower end of that fiber type. a least, most of the time your sets should end right about there. because of course periodization sometimes requires a different rep range for continued progress.
