Lower heart rates (BPM) can be a sign of better efficiency in the heart ( seems like an obvious statement). An interesting study topic is how it can carry some cause for concern of arrhythmias (some benign, some not so much) later in life. The risk seems to grow for older athletes who have been lifelong trainees.
Interesting study topic.
The adaptation isn't
fully understood, but thought to be because of changes in "the pacemaker of the heart"- the SV node. (It's worth noting this was all in folks doing endurance-based events. Not your casual, Z2, 30-minute, 2-3 times per week warrior). Even with that said, mine tends to run in the high 30s/low 40s ad I won't change anything anytime soon.
We did a podcast on the topic with a preventative cardiologist (who happens to be a friend and former colleague) you can check out here if you'd like. The episode might be of interest to the group here in particular as he shares thoughts on ultra training, taxing the heart, the value of HIIT, etc.
The topic came about because I was haunted by the fact that I kept seeing well-trained athletes dying during endurance training/events and wanted to know why. They're linked below or you can search the podcast if you don't want to listen on the browser.
Part 1
Part 2