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Pacing by Numbers: Using Your Heart Rate To Stay Inside the Energy Envelope

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By Bruce Campbell

If you have CFS, you are probably familiar with post-exertional malaise, the severe fatigue that results from doing too much. You can avoid or at least reduce malaise by staying within your limits or energy envelope. This article describes a strategy for staying within one part of the envelope: the anaerobic threshold. 

The Anaerobic Threshold (AT)

The anaerobic threshold (AT) is the heart rate beyond which we draw on energy reserves we don't have and activity creates post-exertional malaise. The threshold is often around about 60% of a person's maximum heart rate, though each person is different and an individual's threshold may vary from day to day or within a day.

(Note: Maximum heart rate is 220 minus your age. For a person who is 50 years old, 60% of maximum heart rate is (220 - 50) x .6 = 102 beats per minute.)

There are at least three ways to calculate the anaerobic threshold. I found mine by observing my pulse in my wrist and noting what levels triggered fatigue. People in our program have used two other methods. Some have been given a stress test on a treadmill. These tests are offered in some doctors' offices and in many hospitals and other healthcare facilities.

Other people have used telephone consultations with the exercise physiologists at Workwell Foundation in California. In these cases, the consultant estimates the threshold using a log kept by a patient of their baseline heart rate and heart rate when active.

Benefits of Monitoring Heart Rate

Once you know your threshold, you can monitor yourself to discover when you are beyond your AT. One way to track your heart rate is to count the beats, as I did, but other people use a heart rate monitor, an inexpensive machine available for $30 and up.

Monitoring heart rate has at least five benefits.

First, it offers control. In the words of one person bedbound with CFS, "I craved a boundary, something I could see or touch that would tell me what was too much. My heart rate monitor is drawing my boundaries for me. When I can manage to get up and move around, but keep my heart rate below 105 beats per minute [her AT], then I know I am safe to continue to do so."

Second, wearing a monitor often leads to recognition of previously unknown limits. In the words of one person, "Just getting the heart rate monitor was a huge eye opener for me...Everything put me over the threshold" Another said, "It was quite shocking to find that I operated routinely above my AT."

Third, the alarm feature of a heart rate monitor tells you when you're about to go outside your limits and alerts you to the need to take a break. As one person says, "We set my monitor to alarm when I reached a bit below my anaerobic threshold. That audible heart rate alarm was the best training tool I could have had."

Fourth, awareness of limits can suggest how to change. One person found that just going up a flight of stairs pushed her heart rate beyond her threshold. Her solution was to stop halfway and rest. Another person says that lifting her daughter used to push her over the edge. Her solution was to sit down and have the child climb into her lap.

A third person found that many activities put her over her limit. She has found ways to be active with less exertion. For example, she now uses a rolling chair in the kitchen, empties the dishwasher in stages, and uses a grabber to pick up things without having to bend over.

Fifth, the monitor helps educate others about limits and to elicit their help. As one person said, "Using the monitor helped my family to understand and they helped me to stop when it went off."
Should You Monitor Your Heart Rate?

The people in our program who have benefited the most from monitoring their heart rate tend to be those below 30 on our Rating Scale and people with POTS (Postural Orthostatic Tachycardi Syndrome). The latter causes a rapid increase in heart rate of more than 30 beats per minute when a person stands up.

Both groups often exceed their threshold doing everyday activities such as those described above. But other people with CFS may benefit as well. For example, finding my anaerobic threshold enabled me determine the level of exercise that I could tolerate without triggering malaise.

If you want to monitor your heart rate, we recommend you discuss the topic with your doctor. As preparation, you can do some informal data gathering. You can make note of your heart rate while resting and also check to see whether your heart rate increases dramatically when you do activities such as standing up, climbing stairs or just being active for a few minutes.

If your heart rate when you are active is near or above 60% of your maximum heart rate, you may benefit from monitoring your heart rate and learning to keep it below your anaerobic threshold.

In summary of the benefits of awareness of heart rate, here are the thoughts of one person who has used a heart rate monitor.

"I've made a lot of progress in the past year, mostly thanks to heart rate monitoring, which trained me to reduce my activity to a level my body can handle. By forcing myself to stay within my limits, I have slowly achieved an increase in what I am able to do without going anaerobic."

"I can walk up a full flight of stairs AND walk down the hall AND brush my hair before I need to sit down for a bit. I've learned to be grateful for these small things. They add up to bigger things. I feel well most of the time now and although I can do very little, it's more than I could do six months ago."

Related Resources

  • Exercise and ME/CFS
    A series of three videos from Dr. Nancy Klimas' Miami CFS Clinic. Includes lab testing to determine AT and tips for creating an exercise program.