Just a quick photo here explaining. This is the exact same gym some time later, and this is the exact end of the floor in the same very pitiful lighting situation. However, instead of using the 70-200 f/2.8L II IS at f/2.8, 1/500, ISO 5000, I used the 135 f/2L, f/2.2, ISO 5000. In post I still had to go +0.40 exposure, but much better.