I am a 58 male. I have 700 or so rides logges all with a HRM. My max HR is 179 which I have observed only 3 times. Only really tough TT's and FTP tests I normally hit around 177. I train regularly, with a coach (who is a Joe Friel accolite :) ). Twice during easy rides I have felt slightly nauseous and seen 220 on my HRM. Only lasted 2 minutes and then back to normal. On one occasion I was cycling past the doctors surgery and managed to get on an ECG machine within minutes of the incident. Nothing found by the doctor. I consulted two separate cardiologists and after wearing 24hr monitoring kit they both said that I should just carry on as normal - it was only of a concern if it started occurring regularly.