This technique takes pain to a new level. It's called a "multi-hold pump set" and it's best done at the very end of a training session. You should only do one set. Here's what it would look like with a triceps exercise:

Triceps Extension: Multi-Hold Pump Set

1. Hold a weight isometrically for 20 seconds, ideally at your weakest point. Then pump out 8-10 reps.
2. Go immediately into a second hold targeting the same point in the range of motion, this one for 15 seconds. Pump out 6-8 reps.
3. Go immediately into a third hold, again targeting the same point, this one for 10 seconds. Finish by doing as many reps as possible.

You'll actually feel your muscles inflate after you're done. It's a very weird but fun feeling. This method loads up the muscle with tons of local growth factors, as well as hyper-saturating it with amino acids.