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Heart Rate and Post-Exertional Crashes in CFS

Posted Feb 03 2011 7:12pm
I've been meaning to write this post for a while now.  Sorry for the delay - we've had some very stressful weeks here lately.

I want to explain what I've learned in the last couple of months about how monitoring heart rate can help someone with ME/CFS to avoid post-exertional crashes.  At the end of last year, I posted a link to an excellent article called "Pacing by Numbers: Using Your Heart Rate to Stay Inside the Energy Envelope," which explains how monitoring your pulse rate can help you to stay within your limits and avoid the crashes we are all so familiar with.  It's an excellent article - I highly recommend you read it - but I wanted to also tell you some of what I've learned from my own experiences recently.

I have no medical background (even though my family calls me Dr. Sue, Medicine Woman now!), so I will try to keep this simple, as I understand it, without too much medical jargon.

Why Do We Crash After Exertion?
We all know that one of the biggest and worst parts of ME/CFS is the exercise intolerance, also known as post-exertional malaise.  When we do too much, we feel terrible the next day (and often the day after that, and so on).  And "doing too much" for someone with CFS could mean taking a shower or fixing lunch or taking a 10-minute walk.  If you want to know more about post-exertional malaise, I recommend Jennie Spotila's excellent series of articles on PEM .

The reason WHY we feel so bad after exertion is because our cells don't handle oxygen the way they're supposed to, a condition known as oxidative stress.  When normal, healthy people exercise, their heart rates gradually increase (which is good for them!), in a process called aerobic exercise .  During this process, the cells are using oxygen in the energy-creating metabolic process within the mitochondria.  If a healthy person exercises for a very long time and/or at very high intensity, their cells switch to anaerobic metabolism.

People with ME/CFS have an extremely low anaerobic threshold because our cells don't handle oxygen appropriately, so that our bodies switch to anaerobic metabolism with very little exertion.  So, the effect of a short walk in someone with CFS can be similar to the effects of a healthy person running a marathon.

According to the pacing article referenced above, you can calculate your anaerobic threshold using this formula
(220 - your age) * 0.6 = anaerobic threshold (that is, 60% of your maximum heart rate)

I'm 45, so my anaerobic threshold is 105 beats per minute.

How Does OI Affect Post-Exertional Crashes?
Another significant factor in post-exertional crashes is Orthostatic Intolerance (OI), a condition that affects just about everyone with ME/CFS.  (If you want to know more, check out this past post on OI ).

OI causes our heart rate to increase and our blood pressure to decrease, often substantially, when we are upright, either sitting or standing.  So, while a healthy 45-year old would probably not hit 105 beats per minute until she'd been exercising for a while, I can hit 105 just standing up.  The result is that even minor exertion can put someone with ME/CFS over their anaerobic threshold.

Tracking Heart Rate
So, monitoring or keeping track of your heart rate can give you a solid, quantifiable way to know when you've passed your limits and are in danger of experiencing post-exertional malaise.  You can check your pulse rate simply by touching your wrist or neck and counting the beats, but I highly recommend using a heart rate monitor.

I asked for and got a heart rate monitor for Christmas (thanks, honey!), and wearing it during my normal daily life has been enlightening.  I planned to wear it when I took a walk or went shopping or something else exerting, so I could tell when I had done too much.  On my first day, I decided to take a walk in our neighborhood, so I strapped it on, after calculating my anaerobic threshold (105).  I was shocked to see that my heart rate just standing in the kitchen was already over 100!  I bent down to tie my shoes, and my heart rate jumped up to 115!!  And I hadn't even left the house yet.

I did take a 15-minute walk that day, as slowly and carefully as I could, but my average heart rate was 103 and the maximum (after I had my shoes on) was 110.

Over the course of the next week, I wore the heart rate monitor almost all the time during the day and watched it constantly (some might say obsessively).  I found that it provided hard data to back up what I already knew about OI (I love data!). 

Even lying down (what's known as resting heart rate), my heart rate rarely went below 90.  Sitting on the couch with my feet up, it was often in the 90's or near 100.  Standing up to make a cup of tea could drive it over 100.  Taking a shower or putting in a load of laundry could spike it up to 130!  One day in the library, I noticed it was close to 100 just walking around slowly, but when I crouched down to see something on a low shelf, it dropped to 75-80.  I knew from Dr. Rowe's article on OI that crouching helped, but it was illuminating to see that for myself.  I also noticed that it varied from day to day, depending on how I felt.

On a grocery shopping trip, I discovered - much to my surprise - that the part of shopping that drove my heart rate highest was carrying the groceries into the house.  This was much more exerting to me than pushing the cart or walking around the store.

It was fascinating for me to see that my quietest day could easily put me over my anaerobic threshold fairly often.  No wonder I rarely felt good - I was in a constant cycle of post-exertional crashes without even "doing" anything!  I really had no idea that was happening.

Try it for yourself - monitor your heart rate for a few days.  Find out where your own aerobic threshold is and how much exertion it takes to put you over it.  Experiment!  Try various normal daily activities and see which ones are within your limits and which push you beyond them.  Figure out how some simple changes can keep you from going past your threshold - maybe dividing tasks up into parts or resting in the middle or delegating certain things.  Once you've determined where your limits are, you can try to stay within them as much as possible.  This should result in feeling better, and then you can try to very slowly and gradually do a bit more.  Good luck!  Let me know about your own experiences in monitoring heart rate.

(NOTE:  You may recall that in early January I started taking beta-blockers to reduce my heart rate.  It's been very, very successful for me.  I will discuss that in another post because this one is already too long, but you can consider various treatments for OI, as detailed in Dr. Rowe's article (linked at the bottom of my OI post ) that can help to reduce your heart rate, thereby giving you more leeway in staying below your anaerobic threshold).
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