My gym has no AC and has never closed, even when its over 100 degrees and humid outside. However, we get a lot more breaks for water and little things that make a difference. Also, my coach can decide if he wants to end early (Our practices are 4 hours long and sometimes he thinks that's too much training time with no relief from the heat) so he can decide if we should end an hour early or something, and he allows us to call our parents, or he tells them in the beginning we may end early today. On some days we practice in the early morning before it gets too hot too. But either way, my gyms never closed!