Several years ago, before I started running, my resting heart rate
was 90. After several months of intense physical exercise, it dropped to the 40's. I measured it on one occasion to be 38. My doctor said I had an extremely healthy heart.
Now, with less exercise, it is in the mid 50's. If you are very active, then 55 is a great heart rate (so long as your BP is good). Your heart is strong enough to pump enough blood with less beats. A strong heart means less chance of heart attack/stroke
-- so good job!
When you exercise, how high does your heart rate get?