[dumbneurologist]

On a tangent: how do you know if the outcome is directly meaningful? that part is easy: ask yourself if you, personally, care. If I told you "an hour of Yoga will make your hippocampus more dense on an MRI" you should

1) ignore me, because that isn't even internally consistent

2) ask yourself why that's a good thing.

Compare that to

"your brain scan in 10 years will show less atrophy", or

"your brain scan in 5 years will show less chronic microvascular injury", or

"your scores in attention and daytime sleepiness will improve", or

"your life expectancy will increase by 4 years"

Those are directly meaningful, because you don't need a doctor to tell you why they are good things (or you do because it's jargony, but a doctor could explain it in one sentence)