lets get concrete with "Exercise": what is one unit of exercise? like exactly what type of movement, at what intensity and duration should be performed how frequently to be as effective as therapy? like should i run every day at 160bmp for 20 minutes? whats the minimum effective dose?
If you take a "brisk" 20 minute walk every day, you'll meet the recommended weekly amount of aerobic exercise for Americans. (I think people should do more.)
The actual amount you need to exercise, or the intensity, is not very big. The good thing with exercise is also that once you make it a habit to walk, say, 20 minutes a day, then walking 25 minutes a day becomes pretty trivial, and so on.
Anecdotally, when I’m depressed, a brisk walk does very little. I need to run to the point where I get the endorphins flowing and there is pain from the lactic acid buildup.
There are no units of exercise and no units of depression either.
In my opinion the best measure of exercise is perceived effort. So while you're asking for objective answers, I think a lot of this is inherently subjective.
The benchmark you're asking for is also ill-defined. For example: How frequently to be as effective as what type and what frequency of therapy?
