Originally Posted by
dominion
Also, if you hit a hill in a race and keep your heart rate constant then you'll slow down, as it takes greater effort to run uphill.
It's interesting to wear a HRM in races occasionally as you can use this data for training. Doing reps and tempo runs at race pace will teach you how to pace yourself, so when you come to races sticking to the pace you want is second nature, without having to check your watch. Sometimes you need to throw caution to the wind and ignore the watch. How do you know how fast you can run until you've tried?