QUICK ANSWER: AS MANY AS YOU WANT _ Longer answer: It's less about exact numbers and more about intensity of effort. You have to make whatever you're trying to achieve difficult in order for your brain to make changes to your body. _ Strong and heavy are relative terms, but if you want to get strong, you have to lift heavy. We'll use the squat as an exercise example. If you squat the heaviest weight you can, you'll only be able to do 1 rep. That's called a 1 Rep Max (1RM). _ Technically speaking, you can train like this: 1 rep of your max weight, rest, go again for desired number of sets. In reality, that's too dangerous for most people. Any deviation from correct technique could cause big injuries. It could also be too heavy for someone to employ the correct technique. _ Dropping the weight down to about 80% is safer and less challenging technique-wise. But it will still be enough of a challenge to create changes in the body. Effort is what counts and because it's now less than the 1RM, more reps are needed. _ Most people can do about 5 reps of 80% 1RM but, again, exact numbers are not important. The same goes sets. Usually 3 sets is needed to challenge the body enough. The first set is like a primer, second set the body really gets going and third set is to make sure it's really challenged. But studies have shown all sorts of ranges, from 1 to 10 to be effective. _ The aim is to just do MORE every few weeks. More could mean adding a few lbs or doing 1-2 extra reps or sets. Which one you pick will be entirely dependent on what works best for you. It's impossible to know that before you try it so you're strategy is this: Pick one and stick with it for 6 weeks, record your results. Try another for 6 weeks, record the results. Repeat, compare, go again. _ I'll wrap up with an example: (Increasing reps) Weeks 1-2: 200lbs - 5 reps × 3 sets. Weeks 3-4: 200lbs - 6 reps × 3 sets. Weeks 5-6: 200lbs - 7 reps × 3 sets. _ At this point you can add weight and start again. If you changed any of those numbers slightly, or increased the sets instead, you would still get stronger. _ Conclusion; there's no magic numbers. Stay consistent and you will win.