If you are physically fit as you say, your resting heart rates are not in a range you should be concerned about, especially with the absence of any symptoms (I assume these are resting rates, say, before getting up in the morning). I am fit, and have measured mine as low as 39. I'd bet it is a little lower than that while I'm asleep and not measuring it. Marathoner Hal Higdon's resting rate was once measured at 29 at the Cooper Clinic, which was the lowest Dr. Cooper ("father of aerobics") says he'd ever measured. (I am not an MD).

Low heart rates are actually good, as long as they are not due to some organic condition.

Just ask your doctor the next time you visit him, there could be some other problem. But as the above poster has stated, typically, an athletic lifestyle is correlated with a lower heart rate. Your heart becomes more efficient at pumping blood, so it does not need to pump so often for the same result.

i do not know if this is the case for a 52 year old man, so I would go ask a doctor.