"I want to tell them how awesome it is that they are doing it, but am never sure if that's the right thing to do some stranger lol."

General heuristic: If you are not sure, if it is right to approach a stranger, just do it. Really. Talk to them next time.

And don't end your sentences with "lol", please.

I go back and forth on things like lol. It's hard to convey in writing when something should be take lightly or as a joke. Without the standard facial cues of smiling it's easy to take something the wrong way.

And in general your heuristic is correct, but the gym is an odd place. I'm pretty social, but would prefer no one talk to me while working out. I'm usually so busy watching the clock and focusing on the task at hand that I don't want to seem rude to someone by having to eventually ignore them to finish my workout.

This is why we have these punctuation marks called "smilies". :-)

(I fear that all the image-substitution of smilies will create a generation of internet users that can't read the original ascii ones...)

Your advice here is good. You might want to quietly watch a few trainers in action, if you can do so unobtrusively - I did, and it helped. I picked a female trainer over a male trainer because I saw a few of the male trainers at my gym barking drill-sergeant-style, and I knew I'd react poorly to that.

As for the complements to a stranger, I did have a couple of random people at the gym say 'you've been working your ass off' or 'you've lost a lot of weight' in a non-creepy way when I was in line at the juice bar and I definitely appreciated it. But everyone's different.

You picked a trainer the right way. If you know what you need to be pushed and motivated then look for that in a trainer. They each have their own styles and personalities just like anyone else.

When it comes to random complements it's really me projecting my anti-social tendency while at the gym. I'm there for one reason and it's to work out. I put headphones and generally don't talk or interact with anyone the entire time I'm there. I guess if the opportunity presents itself I'll try and offer a complement in a non-creep way :)

I think speaking to others at the gym is somewhat cultural.

In lower middle class neighborhoods of Jersey City (JSQ), you can talk to others. Ask for a spot or advice on form, tell them "bad form, watch out", whatever. In Manhattan gyms (at least the 2 or 3 I've used), no one talks to anyone else. Ever.

You might be onto something. In my old city I used to go to an older gym with mainly people who wanted to workout and get strong. The bars had rust on them and the crowd was all very friendly, not big family friendly but they would all say hey when you showed up.

My new gym is a big box gym. It's super nice, and I keep telling a friend of mine that really it's too nice. The people aren't very friendly, but I think that's because there are so many more people working out here that you rarely see the same person enough times to form any relationship. Plus, many people are there to just hang out and act like they are working out. One time I actually overheard a guy ask another guy for a spot and the guy told him no and then walked over to another bench and just sat down. I was stunned and in all my years of working out had never seen someone not help another when asked.

Even in their most competitive days I couldn't imagine Arnold telling Lou no if he needed a spot.

It's possible the guy didn't know how to spot. I'd say no if someone asked me.