15 method – Find a weight that you can do eight full reps. Then find a way to get to 10 reps. Next, do 5 half reps.
21 method – 21′s are best started at the fully contracted position, lowering to one-third of the way down, then back up. If you were doing curls, you would curl the barbell to the fully contracted position then slowly lower it one-third of the way down, then back up seven times.
