Mistake #1: Using The 220-Age Formula
Effective training requires that you perform different types of workouts at various intensities, from low-intensity recovery workouts to high-intensity speed intervals. A heart rate monitor can help you perform each type of workout at the proper intensity by assigning a specific target heart rate or heart rate zone to each. But this only works if the targets or zones are customized to your individual heart rate profile.
When heart rate-based training became popular in the mid 1980s, athletes were instructed to subtract their age from 220 to determine their approximate maximum heart rate, and to perform different types of workouts at different percentages of their maximum heart rate. However, this formula is arbitrary and does not generate appropriate target heart rates for most athletes.
A much better way to determine appropriate target heart rates is to perform a 30-minute simulated race and use your average heart rate for this effort as your “anaerobic threshold” heart rate. This becomes your target heart rate for threshold workouts. Most of your workouts should be done at lower heart rates. Once a week or so, perform an interval workout at a higher target heart rate.