Hopefully what the guys above wrote isn't too confusing for someone new to the game.
"basically", 1-6 reps for strength (CNS muscle fiber recruitment)
8-12 for size
15-20 is often useful for leg muscles
* apparently nothing happens with 7 reps, lol
FYI - just a few days ago, I've started going to 15 reps for most things, just to see and change it up. Unless there is a hot chick watching, lol...then it's all 1 rep power grunts! (kidding)
BUT - this is just a BASIC guideline. Everybody has a different makeup of fast/slow twitch fibers. Alternating between them all is good, especially at the start. Plus, your body is always lazy, and looking for the easiest route with anything - so it will get used to whatever reps you're doing eventually.
Strongmen are typically stronger because of their CNS system. Whenever your brain "activates" a muscle - even though you think the ENTIRE muscle is contracting, it's not. Only a certain % contracts.
This is why/how you can get stronger without getting a bigger muscle. More fibers are recruited in a contraction.
Strongmen (I don't have stat #'s in front of me, so I'm guessing here) probably have trained themselves to fire off at least 90%+ of the muscle fibers when they lift.
Bodybuilders...70-80%....pure guess here...broad stereotype too
I have no idea on endurance athletes, but I'm going to guess they don't fire off nearly as many fibers per contraction as strongmen and bodybuilders - it wouldn't be efficient. They want use as little energy as possible with each movement.
Strongmen typically use up too much energy to last as long as a marathon runner. Likewise, a marathon runner cannot "instantly" use as much strength as a strongman can. Plus there's the whole speed of muscle fiber twitching, etc.
non-workout people <25-50% of the fibers are recruited at each contraction.
Before puberty hits males, this is primarily how boys get stronger. There isn't as much testosterone in their body to grow muscles.
Also can be seen with females - much lest test in their system, yet some girls are so much stronger than others - even if they aren't bigger.
That's my laymen's answer. I'm sure someone of this board can correct/go into more detail, etc. I'm only half-assed educated, and it's late at night, and I already took my PowerFULL, so I'm sleepy, lol.