My first thought was “Do some Z1/2 after your hangboard sessions”, but it seems like they’re quite intense.
I started training for rock climbing a couple months ago (after a ten-year hiatus). So far, I haven’t found the hangboard sessions that stressful, but I’m also being very conservative so I don’t get injured.
So… how long are your sessions? What hangboard protocol are you using? Are you eating before and after?