When did humans begin using gymnasiums to stay in shape, or realize that working out made us stronger?

by another_day

Part of this questions was triggered by movies about ancient Greece/Rome that show warriors with massive bodies (WWE or NFL style) and wondering if humans of that era were able to get that big. Also wondering when humans began working out "for fun" so to speak. Thanks!

400-Rabbits

New commentary is always welcome, but you may be interested in the FAQ section on Did people in the past exercise/work out/lift weights?