Significance of AT

Now that my exercise tests are finished and I have the results, it’s time to figure out what to do about it. I’m relying on the work of Staci Stevens, Chris Snell and others at the Pacific Fatigue Lab who have done a great deal of work on CFS metabolic dysfunction and how to cope with it. Everything revolves around my heart rate at the anaerobic threshold.

The anaerobic threshold (AT) is the point at which most energy is derived through anaerobic processes (as opposed to using oxygen) and lactate begins to accumulate in the bloodstream. As people cross their ATs, they are not able to sustain activity for much longer and experience the rapid onset of fatigue. People with CFS seem to have lower than normal ATs due to metabolic dysfunction, although no one can yet pinpoint where the dysfunction is. While a healthy person can get through work and other activities of daily living without reaching the AT, people with CFS can reach it just by taking a shower. As a result, we experience fatigue much earlier than healthy people and we continue to build up that oxygen debt as we eat, sit, walk up stairs, and so on. Any activity has the potential to cross the AT, building up yet more need for rest. It’s no surprise that we end up prostrate in bed, unable to do anything at all.

Rest and oxygen are necessary for recovery after crossing the AT, but people with CFS do not recover normally. Here’s an example that Staci Stevens gave in an article I wrote in 2010:

An athlete can climb two flights of stairs without fatigue or shortness of breath. A sedentary overweight person might climb the same two flights of stairs and feel out of breath, but will recover completely after a brief rest. A person with CFS may struggle to climb the stairs, and experience severe fatigue and PEM. In other words, the CFS patient reaches the AT after much less exertion than a healthy person, and requires a longer period of time to recover.

People with CFS end up in trouble from two directions. On the one hand, we cross our ATs abnormally early. And on the other hand, it takes us abnormally long to recover. It’s a vicious cycle, and I suspect that many of us spend large chunks of time over our ATs. I saw that in my own test results. One day two, I crossed my AT before I started biking and then biked for 11.5 minutes – all over the AT!!!

Common sense says that if something is bad for you, don’t do it. So the first step is to avoid crossing the AT. Obviously, we can’t spend our days hooked up to EKG and ventilation equipment to carefully monitor our ATs. But we can use heart rate as a proxy for the AT. My heart rate at the anaerobic threshold on day one was 105 beats per minute, and 93 beats per minute on day two. I am now wearing a heart rate monitor (this one) with the alarm set to go off when my heart rate goes over 95 beats per minute.

When the alarm sounds, I am supposed to sit down and rest until my heart rate drops back down. I’m also keeping notes on my activities so I can begin to pinpoint my true limits. If I can avoid my AT, I should be able to avoid taxing my body and triggering post-exertional malaise. Heart rate is not the perfect proxy. For example, my heart rate as I write this blog post is 79 beats per minute, and I will still be fatigued afterwards. But heart rate can at least help get my physical activity more in line with my capacity.

It’s been very surprising to see what activities push my heart rate over 95 beats per minute. Here’s a sample:

  • Walking from the back of my yard up an incline to the house
  • Rolling an empty trashcan up the driveway
  • Pulling weeds for two minutes
  • Walking up stairs at my normal pace
  • Standing at the reception desk at a doctor’s office
  • Laughing really hard (I’m giving my self a break on that one)

The first goal is to get my activity under control. Sometimes I won’t have a choice about going over the AT, like when I go to the doctor this week. But there are a lot of things I would normally be trying to do – weeding, laundry, going to our small farmer’s market – that I am not doing because it sets off the heart rate monitor. It will take some time to see if this really does help minimize my crashes.

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3 Responses to Significance of AT

  1. Eric says:

    Thanks, Jennie, this is very interesting. Keep us updated…

  2. Anne Ö says:

    Thank you so much, Jennie, this is such a great series of blog posts. Please let us know how you get on.

  3. Badory says:

    Dear Julia,Thanks for taking the time to cmonemt. I am sorry my post upset you.I am the first one to admit that I am not a scientist and do not know all that is involved in scientific research. I also couldn’t agree with you more on making sure that the results of this study will hold up to scrutiny. I definitely want them to take all the time they need to design the study correctly, to use proper methods, and to analyze the results carefully. The last thing anybody wants is a study that is not waterproof, especially given that it involves XMRV.I was merely expressing my frustration with what, to me, seems like slow progress in recruiting for the study. It strikes me as odd that I live in the area, but never heard of it until I found out about it recently in one of the online forums. Patients who are not connected to the ME/CFS community simply don’t know about it and that seems like a missed opportunity. This could simply be a result of the fact that the study can’t allocate more money to its coordination and if that’s the case, I am sure everybody would understand. Something tells me that there could also be some complicated internal Stanford politics/procedural rules involved here that outsiders are not privy to. I think some communication with the ME/CFS community about these issues might go a long way in addressing the frustration that’s out there.Of course, it is also possible that patient recruitment is not the pacing item (no pun intended) here at all, so that more aggressive recruitment is simply not necessary. I don’t know. I was simply trying to do my part in helping out with finding participants.

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