> To me the interesting bit is the underlying study showed exercise increased the dementia's progression and was actually harmful. What mechansism's behind that result?

I'm no expert, but the association I had was a podcast I listened once with someone interested in life extension (I think it was on a Tim Ferriss podcast). They spoke about "mTOR activation" (IIRC), the basic idea was that having muscles is good (because they increase the need for glucose, helping the pancreas and the liver in regulating it), but building muscles is potentially harmful, because it causes a release of growth hormone, and essentially speeds up metabolism (and hence aging).

Don't quote me on this, and I'm sure there's better sources of this information out there than me. Does this ring a bell to anyone?