I've always believed my maximum heart rate was 198 based on my performance. I'm 24 years old, so 220-24 = 196, but I routinely hit 197/198 during hard efforts in many rides, and never exceeded 198. When I hit 198 I can barely sustain my level of exertion and have to ease off in short order.
Then one day I blew that number out the window when I sustained 202 for almost 20 seconds on a huge sprint effort. After the effort I had to get off the bike since I was dizzy and could hardly hold my head up and grasp the bars.
So, for the purpose of defining my heart rate zones, is my "max" 202 or 198?