Like any tool, a heart rate monitor only helps you if you know how to use it. The more experience that I have working with runners who use heart monitors, the more I realize that many athletes are training too hard or too easy because they do not realize the variety of factors that can affect heart rate. Let’s look at five points to help you use your heart rate monitor effectively to improve your running performance.
1. Do not use heart rate measured during training to select your racing heart rate.
Several studies from an international conference on the use of heart rate monitors were recently published in Journal of Sports Sciences. Three of those studies reported that heart rate during racing is substantially higher than during training at the same pace. For example, a study from the Sports Science Institute of South Africa found heart rate during 10K racing to be 20 beats per minute higher than while training at the same speed, and during a marathon to be 19 beats per minute higher than when training at marathon pace.
Using training heart rates to select race paces, therefore, will lead to slower than anticipated race times. On the other hand, if you base your heart rate for tempo runs on your heart rate during a 10 mile race, you may end up doing your tempo runs much too fast.
2. Do not use a formula to determine your maximal heart rate.
To set accurate training zones, you need to know your maximal heart rate. Several formulas are commonly used to predict maximal heart rate. All of these formulas are inaccurate. The formulas for estimating maximal heart rate were developed using regression equations, which means that if 100 runners estimated their maximal heart rate using a formula, the average would be almost exactly right. The maximal heart rate for an individual, however, could be off by up to 20 beats per minute.
For example, a 41 year-old runner named Patrick came to the lab for a training program. His estimated maximal heart rate was 179 beats per minute using the formula 220 minus his age. Patrick then went out and did a workout of 2 times 2 minutes hard up hill and his heart rate went up to 194 beats per minute-the formula underestimated his true max heart rate by 15 beats per minute. Prediction equations also lead to overestimation, such as the 20 year-old triathlete who could only get his heart rate up to 187.
3. Measure your resting heart rate immediately upon waking.
To set accurate training zones, you also need to know your resting heart rate. The trouble is, your heart rate increases by about 10 beats per minute as soon as you get out of bed. It can also increase substantially as soon as you start thinking about your plans for the day (newlyweds note: don’t even bother trying to calculate your resting heart rate). To find your resting heart rate, therefore, take your pulse immediately upon waking for several days. Your true resting heart rate is the lowest rate you find. If you take your pulse as soon as you awaken for 5 days and get values of 48, 50, 47, 49, and 51 beats per minute, use 47 beats per minute as your true resting heart rate. If you use an alarm to wake up during the weekdays, then measure your resting heart rate during the weekend when you can wake naturally.
4. Your heart rate increases as you become more dehydrated.
This phenomenon is called cardiac drift and occurs because your blood volume decreases which means less blood is pumped with each heart-beat. A study published in the Journal of Applied Physiology found that heart rate increases 7 beats per minute for each 1% loss in bodyweight from dehydration. If you run for 50 minutes in 70 degree heat, you can expect to lose 1.5-3 pounds due to sweat loss. For a 150 pound runner, that would represent a loss of 1-2% of bodyweight which would increase heart rate by about 7-14 beats per minute. If this runner had planned to do a tempo run at a heart rate of 160-166 beats per minute, his pace would tend to slow as the run progressed. He should, therefore, partially account for this increase and allow his heart rate to increase to about 170-172 beats per minute by the end of the run.
5. Measure your heart rate during a standard run to check your recovery.
In Daniels’ Running Formula, renowned coach and exercise physiologist Jack Daniels emphasizes that the greatest benefit of monitoring your heart rate is to help avoid overtraining. If your heart rate is higher than usual after a standard run at a set pace, then you may be fighting a bug or be overtrained. For example, say that you typically run 5 miles in 38 minutes at a heart rate of 150 beats per minute. If you find your heart rate is 160 beats per minute while running 5 miles at your usual pace, that indicates you should back off for a couple of days before doing your next hard training session. Listening to your body in this way can help keep the flu from making you lose a week’s training, and can curtail over-reaching before long-term staleness sets in.
(This column originally appeared in Running Times Magazine.)