I agree the research doesn't conclusively show direction, but in my experience so many psychiatry correlates are chicken/egg. Depressed people tend to get less

I agree the research doesn't conclusively show direction, but in my experience so many psychiatry correlates are chicken/egg. Depressed people tend to get less physical activity because of their depression symptoms, but too little activity can be quite bad for one's mood. Lots of bad cycles with positive (in a dynamical systems sense) feedback connections.