most likely it was undiagnosed heart disease. His genetics probably pre-disposed him to it. His fitness regime was not and is not a guarantee. We see high school kids die at football practice. I was this guy at 56 and was 95% blocked in my left main coronary artery. I had bypass surgery but I know that every time I get on a bike or go for a hike I could die. I could also die in my sleep. My take is that life without risk is no life at all. I am 70 now and have not missed much but what a miserable life I would have had if I lived in fear and avoided the risks that I have taken.