Here’s one way to do partial reps on a barbell curl:
SELECT A WEIGHT that allows you to curl through just the bottom third of the range of motion (it should be heavier than the bar with which you’d typically do a full-ROM set). Do 8–10 reps restricting yourself to just this limited range of movement.
AFTER RESTING BRIEFLY (15–30 seconds), take some weight of the bar and do 8–10 more reps in the middle third of the ROM.
REST AGAIN, then, using an even lighter weight, perform a final set within only the top third of the ROM. Repeat this sequence one or two more times to fully exhaust the biceps, then move on to full-ROM reps of a different exercise.
You’ll find that you can use more weight working in only the bottom third, and even the middle third, than you could doing a set through a full range. I’ve found the best way to do partials is in a power rack with pins that can be raised or lowered to help define the bottom point of your selected ROM. Sometimes it’s more convenient to do partial reps on a Smith or weight-stack machine, since it can be diffcult to control a bar or dumbbell within a limited ROM. Whichever way you decide to do it, this technique can help you get more out of your next workout. - FLEX