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

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By Bruce Campbell

[Last updated October 4, 2021.]

The heart of successful management of ME/CFS and fibromyalgia is pacing, which involves finding and staying within the limits imposed by illness. By pacing, you can avoid the out-of-proportion intensification of symptoms called post-exertional malaise (PEM) and increase your chances for improvement.


The Anaerobic Threshold (AT)

This article describes how to find and stay within one limit, the anaerobic threshold or AT. This limit is the heart rate beyond which we draw on energy reserves we don't have, triggering post-exertional malaise. 

Calculating the Threshold

There are several ways to determine AT. One is to estimate the threshold as 50% to 60% of your maximum heart rate, which is often calculated as 220 minus age. For example, a person 50 years old, the threshold would be estimated at (220-50) x .6 = 102 beats per minute. 

Second, some people in our self-help program report having found theirs by having cardiopulmonary exercise testing. This testing is offered in some doctors' offices and in many hospitals and other healthcare facilities.

In Fall, 2020, the well respected researchers at the University of the Pacific suggested using 15 heart beats per minute over resting heart rate. Thus, if your resting heart rated is 85, your AT would be 100. (For more, see discussion of morning resting heart rate later in article.)

I used a fourth way, observing my pulse in my wrist and noting what rate triggered an intensification of my symptoms.

Experimention and self-observation can be crucial to understanding what circumstances raise your heart rate.  Physical activity is perhaps the most obvious, but there are many others.

For example, one person in our program reports that being in a noisy environment "can cause my heart rate to increase by 40 beats per minute. Stress and socializing are big triggers for me." You'll find other triggers mentioned below.

The principle to remember is your AT is the heart rate beyond which you trigger post-exertional malaise (PEM).

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 many people use a heart rate monitor, such as Polar FS, FitBit, Garmin, and iWatch.

Monitoring heart rate has at least five benefits.

1 Helps Define Safe Activity Level

In the words of one person bedbound with ME/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."

2 Brings Awareness

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 that she was surprised at some of the things that put her over her threshold, including many social activities, talking on the phone, eating some foods, watching news on TV, and repetitive motions like chopping vegetables. And a third commented, "It was quite shocking to find that I operated routinely above my AT."

3 Provides Advance Warning

Some heart rate monitors have an alarm you can set to sound when your heart rate nears your limit, giving you time to change what you're doing and avoid a crash.

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 for staying within my AT."

4 Gives Stimulus to Change
A monitor brings awareness of limits and 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 pushed 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.

A fourth person echoed the idea by saying that being aware of the importance of controlling her heart rate helped her to slow down. "My natural tendency is to move quickly and multi-task. Knowing the importance of heart rate motivates me to slow my overall pace.”

5 Educates Others

A heart rate 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 help me to stop when it goes off."

Summary of Benefits

To summarize 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."

Morning Resting Heart Rate

The strategies above show how you can use observations of your heart rate during the day as a tool for staying within your energy envelope.

You can also use what is called the morning resting heart rate in combination with a simple log for the same purpose. (This strategy is strongly recommended by Dr. Klimas and Connie Sol of the Nova Southeastern University Institute for Neuro Immune Medicine in Florida.)
You can determine your resting heart rate by lying down shortly after getting up in the moring but before taking any stimulants such as coffee, noting your heart rate at that time.

By doing this for a week or two and keeping a simple log of your symptoms and energy level, you can determine your baseline morning heart rate and also should see patterns between overactivity one day and subsequent elevated heart rate. The elevation often occurs the next day but may be appear two or three days later.
Here’s how one person in our program describes her use of this technique:
"I used the average of my heart rate over two weeks to determine that my baseline resting heart rate is 66 beats per minute. By keeping daily records, I found that if the heart rate at that point in the day is five or more beats higher than that threshold, I continue to have a higher than usual heart rate and increased fatigue for rest of that day or even longer."

"I also noticed that the increased pulse rate can often be predicted by the level of activities and stress in my life in the day or days previous to the raised pulse."
"When I have an elevated morning heart rate, I replan my day to have less activity than normal and more rest. I can avoid increased symptoms if I double my normal daily flat rest time and postpone all high intensity activities until my morning resting heart rate stabilizes again at 66 or below."
Should You Monitor Your Heart Rate?

Many people in our program, with a wide range of severity in their ME/CFS and/or FM, say they value monitoring, so we suggest everyone explore to see whether monitoring heart rate might be beneficial for them. Those 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 Tachycardia Syndrome).

Both people below 30 and those with POTS often exceed their threshold doing everyday activities such as those described above. By monitoring their heart rate and adjusting how they go about their activities, many find they can slowly improve and increase the activity they can handle without triggering a rise in symptoms.

Other people with ME/CFS/FM may benefit as well. For example, finding my anaerobic threshold enabled me to determine the level of exercise that I could tolerate without triggering post-exertional malaise. Staying within my AT helped me regain strength and further reduce my symptoms.

(Note on POTS: POTS affects heart rate somewhat differently than ME/CFS or FM. First, it causes a rapid increase in heart rate of more than 30 beats per minute when a person stands up but the rate
may quickly settle down once the person with POTS is walking slowly.

People with POTS have more difficulty than normal with quiet upright postures, so slow movement of the leg muscles can help settle down their heart rate. If the heart rate of someone with POTS remains high during their activity, then laying back down is an important tactic to keeping their heart rate below the AT.)

If you are interested in finding your AT, you can start by making 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 so, you may benefit from monitoring your heart rate and learning to keep it below your anaerobic threshold.