Many things attribute to a resting heart beat/pulse... lifestyle, sleep, stress, diet, Training, and attitude. I don't call myself a Personal trainer because that title has been watered down over the past 20 years since i got certified. I now call myself a health & fitness Practitioner for my own well being of not be pooled in with other PT test takers, and my 50yrs of experience has taken me a lot further than any certificate can.
My resting heart beat in the Morning upon waking-up is in the mid 40s, at rest during the day/night watch TV/reading/Computer can range 50s to 60s, and I'm not a big Cardio person, matter fact, NO short, or extended Aerobic exercises at all, but i do train with high Intensity. Your question can be a loaded one, since many variables can attribute to a low, or High pulse rate.