Yesterday I went to see someone I use to do a digital face scan (Visascan). We had to cancel a previous appointment because she broke her arm and her arm was in a cast.
Because we discuss longevity issues she mentioned that she has to cut her nails in the arm that is not broken, but the finger nails in her broken arm (in the cast and therefore immoblised) had not grown.
I think this is a useful anecdote as it is another example of the idea that using part of the body affects growth and development in another part of the body.
I think this is the Hypoxia Inducible Factor, but it is clearly transferred in the blood as well as using HIF 1 alpha in the cell.
There was a similar example showing that exercising one arm can cause another immoblised arm to see muscle growth.
The anecdote shows that this is to some extent localised.
Incidentally I measure nail growth as it is an indicator of stem cell availability.