Is it a good idea to engage in relatively heavy session of upper body + core calisthenics (read, push-ups/pull-ups/chin-ups) about 12 hours after a long run (10k+) - assuming one is feeling fine and not exhausted, but heart rate still a bit high?
If not, how much gap is ideal? Should one wait till the heart rate comes completely back to normal?
If you run first, you’ll do better at the run and have better results from it, while the body weight work won’t be quite as good as it could be. Vice versa for doing the body weight stuff first. Depending on your intensity, you could do one right after the other. In your question you ask about doing them separately with 12 hours of time between them which is more than enough assuming that you’ve got the proper nutrition supporting your efforts.
As for how low your heart rate should be? Low enough to be able to speak and have a halfway decent conversation. I don’t see any reason why you couldn’t jump straight into body weight work after 20 minutes or less.
