So I know fitbit heart rate monitors are wildly inaccurate blah blah blah but since I'm just measuring against myself i'm hoping this makes sense.
When I first got my fitbit my running gave me a heart rate which was in the "peak zone" for pretty much all of every run (last Sept). I never worried about it as I felt fine.
Over the last few weeks however, fitbit has been decreasing the percentage of my running which is taking place in the peak zone and this week, I had my first run out (5k on my normal route for evening with 89m of elevation) where the whole run was in the "cardio zone".
My pace was similar, the route was familiar, I felt like I was working just as hard. BUT I did have something left in the tank at the end. Does anyone know why this might have happened? Am I getting fitter or is my fitbit learning more about me or something else? Peak heart rate on runs also seems to have dropped.