A heartrate of 60 and below is called bradiacardia (sp) so well done gr8
Below 60 is actually good if you are an endurance athelete. It's only a problem if there is no explanation for it.
Exactly thats why I said "well done" Its an indication of left ventricular hypertrophy, stroke volume and an improvement in parasympathetic tone. It is good you are quite right. You are also right when you say its only not good when there is no explanation for it. But this is rare.