Heres my little story on my heart ... Im 49years old and after a recent ECG at a company medical I had a "worried urgent" call from the doctor. He said he was about to go away for the weekend but felt he should warn me as they were worried about my test. The electrical heart signals were peaky and indicative of some potential problem.
He told me not to get my heart above 120bpm and walk but not run anywhere!! He knew I was a keen cyclist ....I said that wld be hard as I had a 1hr ride home from work and an approx. 3hr XC ride the next day. Anyway it worried me and I saw a cardiologist the next week. They did an ECG as well as an ultrasound scan to check to see if there was any thickening of the heart muscle which could be indicated by my peaky ECG. The cardiologist said the my heart was in great shape and all fine and nothing to worry about.
I would have been even more worried if a non medical mate hadn't already warned me that its quite common in people who do a lot of endurance sport to have the peaky electrical signal. My resting in daytime is about 57BPM but flat out about 188bpm. As said above it seems to vary widely with different individuals .