I think the trouble with Bradycardia is that the term is applied to any HR lower than the "normal" range whether or not it has any clinical significance. My resting HR has always been slow. In periods of my life when I've been unfit - busy, sedentary job, not much exercise - it was around 54. When training for racing it was around 43, and it still gets down there sometimes when I go on extended tours and am knocking out 500km per week. When just riding a fair amount - say 8 hours a week - it's usually about 48.
My view is that as long as this continues, and especially as long as it responds to varying training volumes in this way, it's no problem. If it dropped into the 30s and stayed there, I'd be taking some advice.