Something I have found very useful for some athletes is monitoring HRV – the app HRV4training is the best. A few good studies have looked at HRV guided training, and anecdotally I have used this myself. I use HRV as ‘one last final check’ – a green light if you like, before going hard. Once a good baseline HRV reading has been achieved (several months is ideal) you can then use HRV with decision making. If you’re feeling good, and the effort is easy, as in the above scenario, AND the HRV is good, then I believe that is an IDEAL time to add in some intensity, whereas if the HRV is a bit off, I would tend to hold back. I would certainly not let HRV guide all of my training, but it’s a good confirmation that all systems are go!
https://pubmed.ncbi.nlm.nih.gov/31490431/
https://pubmed.ncbi.nlm.nih.gov/26909534/