Another thing to consider: Statin cholesterol drugs, such as Lipitor.
old people sometimes tend toward higher cholesterol, so their docs put them on statins.
Mine did and within two weeks I started having calf issues, particularly when increasing run distance and/or intensity. It took us two years to figure it out.
Short story - research indicates statins aren't good for muscles especially those of runners.
Since getting off statins over two years ago I've had no calf problems.

totally different muscle pathology

I'll have to take your word for it.