My exercise test results are in. The numbers were, quite frankly, shocking. Two numbers – VO2max and anaerobic threshold – provide the evidence that I have significant metabolic dysfunction, and I’ll try to explain what they mean. Check out my description of the test itself for background. What I do now that I have the results will be the subject of my next post.
VO2max is a measurement of the maximum amount of oxygen that a person can use during exercise. The more oxygen you can use, the more energy you can produce. VO2 max is considered the best measurement of a person’s physical fitness or functional capacity, and it is affected by factors such as age, gender, training, altitude, etc. A sedentary woman my age has an average of 27.0. My VO2max was 20.7 on day one, and 19.6 on day two. In other words, my maximum ability to use oxygen is 23% lower than what would be expected for a sedentary woman my age.
One interesting thing about my VO2max number is that I was able to reproduce the result on day two. Typically, people can reproduce their VO2max value on a two-day test with about 6-7% of variation. My number was about 5% different. So this is a good thing, but not necessarily typical of CFS patients. One study found that CFS patients had a drop of 20% in their VO2max on the second test day.
Dr. Betsy Keller of Ithaca College, who conducted my exercise test, included functional equivalents in her report to help translate the numbers into information I could actually understand. Looking at just the VO2max number, my capacity equates to slow cycling, but carrying groceries upstairs exceeds my functional capacity. That’s pretty grim.
Anaerobic threshold is where things get really interesting. The anaerobic threshold is the point at which your body is producing most energy through anaerobic metabolism, as opposed to aerobic metabolism which uses oxygen. This means that you will feel increasing fatigue, your workload will drop, and you will have to stop activity within a few minutes. It also takes longer to recover from this kind of activity, requiring rest and more oxygen. (Is this sounding familiar to anyone?)
On day one, my anaerobic threshold occurred at 105 beats per minute. That is not horrible, although it is low. A deconditioned but otherwise healthy person might have a result like that. On day two, however, my anaerobic threshold dropped to 93 beats per minute. That is abnormal, not just because it is low but because it represents such a significant drop from day one. Healthy people, even deconditioned people, are able to reproduce their anaerobic threshold results on day two. That I failed to do so is proof of metabolic dysfunction.
When you put the VO2max result together with the anaerobic threshold result, you can see the metabolic dysfunction another way. Normally, the anaerobic threshold will occur at about 50-75% of a person’s VO2max. But for me, my anaerobic threshold on day one occurred at 30% of VO2max. Anything below 40% is considered an abnormal result and evidence of metabolic dysfunction. On day two, my anaerobic threshold occurred at 17% of VO2max. That is crazy low. In fact, I reached that anaerobic threshold just sitting on the bike before I started pedaling on day two. Just sitting there, I was already maxed out. These are grossly abnormal results.
To equate these numbers to functionality, Dr. Keller said that my day one anaerobic threshold is the equivalent of standing to fold laundry, or putting clothes in the washer, but that walking around to put away laundry would be beyond my capacity. But on day two? The day two result is the equivalent of lying down watching television. So when I am in a crash, I am exceeding my anaerobic threshold by just lying down and watching tv or doing nothing.
So no wonder I feel like shit all the time, yeah?
There were other abnormalities, including blunted heart rate and blood pressure responses, but these two numbers are the key for me. As Dr. Keller points out, most activities of daily living require me to work above my anaerobic threshold. This means my ability to perform those activities is limited, and resulting fatigue prevents me from continuing to perform those activities.
Here’s the killer fact for me, though. On day two, I was at my anaerobic threshold before I even started cycling. Then I proceeded to cycle for 11.5 minutes, and came close to the length and workload I produced on day one. The whole second day was past my anaerobic threshold. I felt and rated day two as more difficult, but I kept going anyway. I draw two conclusions from this. First, I have become accustomed to operating over my anaerobic threshold and have probably developed that as an adaptive coping mechanism. Second, I cannot trust my my own assessment of when I am overdoing it. My sense of how I am feeling is not reliable.
My husband’s reaction to that was “Duh.” It will surprise no one who knows me that the test proves I am a stubborn and determined woman who does not accept her own limitations. But it was a shock to see this reduced to numbers and written in black and white on the page.
A friend pointed out to me that nothing has actually changed. It’s not like I’ve suddenly developed a heart condition. The only thing that has changed is the information I have about the metabolic dysfunction. Knowledge is power, and next time I’ll share what steps I’m taking to apply this knowledge.