I trained briefly in a health club/gym pool (not full length, had a sauna etc). I would usually find that after swimming in it for any length of time, inhaling fully wouldn't feel like it was providing me with the expected amount of oxygen - hard to describe accurately the feeling but it definitely wasn't just breathlessness from exerting myself. Didn't really hurt or anything. When I swam in a proper fitness pool however, there were no feelings like that.

Have you ever been tested for asthma? I used to get that feeling all the time when doing rigorous exercise, and I was always under the impression that it was related to my asthma in some way (I could well be wrong though, I can't remember where I learnt this).

Pool swimming is one of the least likely triggers for exercise-induced asthma. The air above the surface of a pool tends to be warm with very high humidity, which is the ideal air for an asthmatic.

If a person gets that feeling after any exercise, yes, it's not a bad idea to get checked for asthma. But if it only happens after swimming, I would think it much more likely that the issue is related to that pool.

Chlorine allergy is also a possibility, if the person experiences symptoms in pools that don't occur elsewhere.

I remember it happening to me in some public pools but never in the ocean.

I've also done some high intensity training outside of water without the same lung issues. I'll get out of breath after running for a while, but the pool related issue is every time I breathe in deep to expand my lungs, it would feel very strange and hurt. It would last even an hour after leaving the pool area.

Never been tested and generally speaking I rarely suffer from chest issues. I have no problem exerting myself in a well maintained pool (or whilst running or cycling), it was just a particular experience I had in a poorly maintained pool.

That’s the feeling I get after walking or cycling in London traffic and getting a lung full of diesel fumes...

I normally get that feeling when exercising on open trails as well or even indoors. It's part of exercising intensely

Perhaps, but it feels much worse in a polluted environment, and takes much longer to go away (lungs still sore/“tight” hours later).

I do think it’s strange when I see people jogging along polluted arterial roads for this reason. Especially when there are often traffic-free trails or quiet back roads available nearby!

Interesting to hear it is a notable effect, I've never ran in a polluted environment before. Next time I'm in New York I'll have to give it a try.

New York is notably less polluted than many European cities. For one thing, there are far less diesel vehicles. The US has long had stricter and more effective vehicle emissions rules than Europe.

That's the same feeling most humans get when they're exerting themselves in an environment with lots of airborne particulate matter.

Some are more sensitive to chlorine than others. I have astma and feel awful after having been in a pool.