50's is perfectly normal for someone who works out regularly.
Achieving mid 40's typically requires people to work out regularly with some intensity. "Fitness enthusiast" may well achieve this level, without necessarily pushing yourself to 'professional athlete' levels.
My guess is that your RHR is "lower than average, but still within the normal range for someone of your fitness". Remembering of course that 50% of the population are "below average".
But if you are concerned about it, you may want to speak to your doctor - he would have a better idea of acceptable ranges. Mid 40's can indicate a problem, or it can just be a sign of a good level of fitness.
The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.
| current weight: 178.0