TL;DR – It doesn’t matter, in theory. Muscle growth is largely based on volume, so whether you do 5×10 or 10×3, as long as it hits the same volume it doesn’t matter too much. That being said, it’s much easier to do 5×10 at 50% of your 1RM than 10×3 at 85% of your 1RM. Low intensity is easier to recover from and stick with, and thus is generally the best approach to getting bigger.
Now for a little more in depth.
The thing with lifting low weights is that it’s more of an endurance race as opposed to your muscles running out of juice to lift the weight. Heavy weights are taxing on your CNS, and thus take a great deal more effort with each repetition than low weights. If you want to experience it first hand, go compare Squatting 5×10 @50% with Squatting 10×3 @85%. While the volume here is equal, the latter will cause a far greater amount of stress on your body as well as taking significantly longer due to increased rest times.
That being said, if your goal is strength then lifting heavy is the best way to get better at lifting heavy, a generally understood idea. If your goal is to increase strength, however, then you should look for a balance between the two in your workouts. A generally accepted method is called undulating periodization, a phrase I’ll cover in a later post. The general idea is to alternate intensity and volume throughout the week such as:
- Day 1: 5×10 @50%
- Day 2: 5×5 @75%
- Day 3: 6×3 @ 85%
Or some sort of variation like that. This way, you’re including a good amount of volume along with sets to get you better at lifting heavier. And, generally speaking, if you can lift really heavy things, you’re probably going to be fairly large.