Step by step, mile by mile

Your RHR is in the low 30s? Are you sure you are still alive?I just took mine. It was 48. You must be in super shape.

The 10 miles runs must be starting to become pretty easy for you now.

Haha yes I'm pretty sure I'm alive, even when I was in high school and running less my heart rate was still around there. Averaging under 120 for 10 miles is crazy though, I'm definetly in the best shape of my life, and I still have so many things to add on to get better(weights, drills, strides, plyometrics, maybe even a workout or two :) ) so I'm very excited for the future.

HR is meaningful only in context, and even if you know resting HR is not a good reference. If you know your max HR and resting HR, that is better, but still not perfect. The reason is a large degree of individual variation. E.g. back when I cared to measure it, with the resting HR of 48 and max HR of 170 I had 120 at about 7:40 pace, 144 at 6:00 but raced the marathon at 163 at 5:30 pace - not something you would find in a textbook. That is why I do not bother looking at the easy run HR. If you are hitting a performance limit, it is sometimes useful to see if your HR is rising or staying steady and maybe even dropping as you reach the point of not being able to continue at your dream pace. For the easy run, just run an easy effort. For the hard run, run a hard effort. Learn to feel the effort, because there are multiple things to be aware of and all of them matter - as in it is a bad idea to overtrain them as well as undertrain (though overtrain is usually worse) - muscle, bone, tendon, and ligament strain, nervous system/endocrinal system strain, and cardio strain. Remember the principle of the weakest link in the chain - you need to train at the optimal level of effort for your weakest link, and increase the effort only when the weakest link has gotten stronger. As those things are next to impossible to accurately measure - even in a lab, and especially at home - you have to learn to feel them. You can tell you did it right if you are getting faster and are not getting sick or injured. Optimal stress also depends on what you are doing to recover - if your recovery routine gets better you can take more stress.

Thanks for the input Sasha - I totally agree on running on feel over any other indicator, I just thought it was worth mentioning how low my HR for running this much is now compared to the past. Guess I'm doing something right if the blog creator is finding time to check mine!

Decreased HR at the same pace is definitely a plus.