Triples

These are so named triples, 30's, 18's, 24's, 21's etc.  Why are they named like this?  It's simply based on the repetition scheme.  Lets say I choose 15's.  I would choose an exercise and split the reps into three sections.  A lower section, an upper, and a full section.  Lets use leg extensions to illustrate it.  I would begin by performing 5 half repetitions from the bottom range of motion until I reach the midway point of the exercise.  After which, I would perform 5 half reps at the top range of motion.  Following this, I would perform 5 full reps.  Anyone who makes it through this method on the squat, has an amazing pain threshold for sure!