This is a good article on the subject:

http://www.muscleandstrength.com/articles/truth-rep-ranges-muscle-growth

Sounds like the people at your gym may need to be pointed to the article as well.

Generally speaking, high weight/low reps gets you stronger (1-6)
Moderate weight/median rep range gets you hypertrophied, and it's what bodybuilders do (6-12 reps)
Lighter weight/higher rep range gets you endurance (12 reps and above).

You can of course switch things around and combine them, but unless you focus on one, you won't make optimal gains.

Then again unless you're a professional body builder or power lifter or endurance athlete, the word "optimal" doesn't really apply. So basically, as a regular person who just wants to be fit for themselves, just do whatever you like.

I personally focused on strength for a while, then switched to hypertrophy for a few weeks to try it (didn't like it), went back to strength and am now taking a break from that to focus on endurance for a while while still working on strength, but at a lower pace.

There really isn't a "best" way to do it, and it really depends on your goal, what you enjoy, and what you want to accomplish.

Hope that helps you.

Well there are optimal programs in regards to your goals and your experience level.

For a beginner lifter, strength programs like Stronglifts and Starting Strength are optimal because they focus on form and take advantage of the new lifters ability to progress in their lifts, meaning they are able to increase weight very regularly.

For an intermediate lifter you will find that many programs almost cross over from strength into hypertrophy because they both certainly do serve a purpose.....but again that is dependent on your goals.

But yes 1-5 reps at heavy weight is strength, 6-12 reps at moderate weight is hypertrophy and 12+reps is endurance

And the reason why we do 5 reps with these programs is because it's a snug mix of strength and hypertrophy.

"Hypertrophied" basically means "overgrown". It means the big, bulky muscles that body builders work for. There's a lot of women body builders out there that like bigger muscles on themselves also. But,a lot of that isn't achieved with weight training alone. At some point, to look "big" as a woman, you have to consider taking hormonal supplements and/or steroids, because we're genetically limited, so don't be afraid of lifting even in the "hypertrophy" range because your natural muscle size is going to be limited by genetics and hormones anyway, and it's up to you (within those limits) how far you want to take it.

I aim for functional strength and endurance, more so than for looks. I basically train so that I can do things better and easier in real life situations, and for health reasons, not for the sake of sports competitions or whatever. But everyone has their own goals.

English isn't my native language either. It's German, actually. If you speak German, let me know, and I can try and translate for you. I see you're ... Danish? I don't speak that, sorry.

I've made more progress at both strength and improving the size and shape of my muscles, from 5 weeks of stronglifts than I did from 3-4 months of bodybuilding style training prior to that. (and I even had to repeat 1 week of stronglifts as I was ill and lost 6lb in 2 days and took a while to get my strength back, so I'm still only on week 4) I gained more from the 3-4 months of bodybuilding style stuff than I did faffing around with dumbbells while eating at a deficit (although I did get my body fat percentage from obese to healthy, so it wasn't a complete waste of time)

in any case, I'm sticking with stronglifts and whatever similar kind of thing I'll graduate onto when I finish the 5x5 program