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!