I am 47 and my resting HR varies from 32 when well trained to 36 when detrained. There is genetic and age element as well.
Back in Feb-Mar it was 32 - 33 BPM. I had to go to the Doctors for what turned out to be Anaemia (not great thing to suffer from for an Endurance Athlete,) but before that they did all the normal checks and on discovering my HR was 33 sent me for a ECG.
When they hooked me up I was expecting the reading to be 10 BPM or so higher from running around from room to room and the stress but on the bed it was 33. The nurse that ‘plugged me in’ so to speak, noticed I was wearing running clothing (base layer) and said “Are you a Marathon runner” I replied “No., I cycle a lot and have a history of Endurance sports, I ran before knackering my ankles, wish I still could, love running.” She replied, “I thought so, noticed your base layer, suspected Marathon runner and I said to myself he is going have a low HR, expected about 40 but yours might be the lowest I have ever seen.”
Long story short, checked out okay and we had a good chat about heart rhythms and pulses rates.
She pointed that out.
She also pointed out the amplitude on the Booms is different.