low resting heart rate?

Question

why does an athlete have a lower resting heart rate than the average male

Answer 1

Exercising the cardiac muscle makes it more effective thus it does not have to pump as hard to do its job.

Answer 2

It is a normal compensatory mechanism of the heart after doing a prolong exercise, so during exercise the heart rate reaches it's optimum, hence the heart compensates by relaxing i.e beats at a slow rate during resting phase(IN ALL NORMAL SUBJECTS).
However this is not the case with a pathological heart, it's due to excessive oxygen in blood, or if patient is on beta blocker.