It’s a perfectly good question, and there’s no simple answer. In fact, a number of variables are in play here, so let’s go through them one at a time. Doing so will allow you to customize your training program to ensure you’re using the right weight every time.
You can pick up a 20-pound bar, curl it 75 times, and, after a while, you’ll become fatigued and your arms will get pumped. You’ll certainly be sweating a lot. Conversely, you can pick up an 85-pound bar, curl it 8 times, then have to drop it because you can’t do any more reps. In both cases, you trained “hard.” But is one approach better than another?
It may surprise you to learn that the answer changes depending on your goal. If you’re looking to get as strong as possible, you’ll be using a heavier weight than someone who is trying to get as big as possible. And to improve muscular endurance, you’ll use an even lighter weight.
Strength training means choosing weights that allow you to train in a rep range of 1-6.
Building muscle mean choosing weights that allow you to train in a rep range of 8-12.
Focusing on muscular endurance means choosing weights that allow you to train for at least 15 reps