My wakeup HR was 57 today. I felt great, so I added about 0.1 mile and jogged around the 0.6 mile loop that my wife and I walk. I felt fine at the end. Getting past the 0.5 mile marker is an important event for me, because it takes me about half a mile to warm up. Once I'm past that point, I run better and, I assume, get more enjoyment and benefit from the run.