Just 35 minutes per day of physical activity can help combat depression and anxiety even in the most severe pathological cases and among those who are genetically predisposed toward it. At least, that's what the foremost researchers in the world say after decades of treating patients who are so afflicted with mental health issues that they're hospitalized and in some cases incapable of functioning in work environments or just general day-to-day life.
Massachusetts General Hospital has a very long track record of treating untold numbers of patients with depression and anxiety. They have a whole section of the hospital devoted to it. Harvard researchers released numerous papers from the massive dataset of patients there, one the most recent concluding that as little as 35 minutes of basic physical activity can reduce new episodes (either the frequency or duration and/or magnitude): https://news.harvard.edu/…/physical-activity-may-protect-t…/
Specifically, they’ve focused on how this intervention might help people who are genetically inclined toward the pathologies. And the summary is “genes are not destiny.” Moreover, this finding is in large part based on hospitalized patients, and therefore flies in the face of people who argue "you can't understand MY level of depression/anxiety." That personal fable doesn't hold up well, given that inclusion criteria maintains participants whose mental disease is definitely worse than "YOURS."
Now pay attention: the paper isn’t preachy, and it doesn’t say “CURES”. So people on either end of the philosophical spectrum need not get excited. There’s nothing to argue against here. And there’s nothing to overstate. The finding is that physical activity improves the outlook. It isn’t THE cure. And there’s no need to dismiss it in order to self-reinforce ones helplessness or hopelessness. These aren’t a bunch of armchair philosophers doing a thought experiment. These are legitimate researchers stating findings from a broad sample.