I personally find that exercise only contributes to good mental health outcomes when it is part of a system that monitors and directly, daily, addresses issues of physical exhaustion. Experiencing exhaustion and a desire to push through it was my personal #1 link to depression and anxiety. I found that just laying in bed and relaxing has a much higher likelihood of vanquishing my depression and anxiety than exercise ever did, and exercise, even a simple walk, can actually make the symptoms worse by contributing to the exhaustion.

This is _my own analysis and experience_, of course, so YMMV. There are additional important approaches to anxiety, like identifying stressors that need to be addressed (situations, goals, relationships, etc.) and attending to various facets that contribute to a feeling of purpose and promise. But after learning to look at my symptoms through the lens of "exhaustion" (whether it be productivity exhaustion or fitness-induced) I no longer suffer from chronic severe anxiety and depression, and my psychiatrist long ago pronounced me cured. Some people here may benefit so I share this in case it helps.