It is nice to see such a

It is nice to see such a large study really show the holes in the tendency for us to infer causation from correlation just because it "seems" right. It is kind of a jolt to suddenly doubt the seemingly obvious conclusion that exercise helps elevate mood, but this study really catches the attention.

That said, I personally feel the effects of elevated mood after and during exercise. But if I were depressed, it would be kind of begging the question to ask whether exercise lifted my depression or whether the lifting of my depression helped me have the will to get out there and exercise!

I doubt that exercise is as great a prescription as the correlational studies seem to suggest. It helps you feel better, as long as you feel better enough already to do it! But suggesting exercise as something that may help is a good idea, because it might help, and if you're already on the way up, it might help lift you higher. It does that for me.