I am an athlete (the steeplechase) so what I really will like to know how I know that I am working out at the 70 to 75% cardiac capacity when I go in my runs. I have been using the 220-age times 70% formula, but I don’t think it is accurate. It has me try to do workouts at 106 beats per minute but that is too low (easy) for me. I usually maintain a 125 to 130 BPM for about an hour and 40 minutes. I will go higher (160 to 180) when I am either training hard during intervals or racing. Being an athlete for 55 years.