And the benefits build up even more if one takes some of that physical activity outdoors. I'm convinced that a big chunk of mental problems today are just due to people being removed from their natural environment. You can't expect a dog to be well adjusted if he doesn't go for walks. Similar thing with humans. We evolved as a very mobile species of hunter/gatherers. You can't just stick the product of that evolution into small enclosed spaces all day and expect nothing to go wrong.