My maximum heart rate has been calculated as 154. The calculation was done during a medical sports test with heart and lung equipment at the hospital. The heart rate on my watch sometimes hits 220 generally at the beginning of a run when I am only warming up. I returned my watch to Tomtom to be checked out but there is no change in the HR registration. This sucks as I am training for a marathon at a specific HR. Is this a common problem and does anybody have a solution to it?