It has been more than a year since I had a two-day exercise test. My exercise test report was full of all kinds of jargon, and over the last year I have been trying to decode and apply it to my pacing. One of these concepts is “METS,” a measurement of the effort needed to do an activity, and correlating my results to the real world has been nothing short of shocking.
METS is the Metabolic Equivalent of Task, and is a measure that expresses the relative energy cost of activities, with a MET of 1 equal to sitting quietly. Walking at a slow pace has a MET of 2, meaning that walking slowly costs twice as much energy as sitting quietly. In exercise testing, METS is calculated from the maximum amount of oxygen consumed (VO2max), although it is not intended to perfectly correlate to an individual’s metabolism. But for purposes of understanding the relative costs of different activities, and estimating parameters of an individual’s functional capacity, METS is used as a standard measure.
In my exercise testing, my VO2max (which is the maximum amount of oxygen I consumed) correlated to 5.9 METS. This means I can’t do any activity that requires more work than 5.9 METS because my body can’t perform that level of work. My anaerobic threshold (as I’ve previously explained) was very low. A healthy person with a maximum METS of 5.9 should cross the anaerobic threshold between 3.0 and 4.425 METS. In the first test, I switched to anaerobic energy at 1.9 METS. In the second test, my anaerobic threshold occurred at 0.92 METS. Needless to say, this is abnormally low!
The real value of METS is in understanding the energy cost of activities relative to each other. The Compendium of Physical Activities is a list of the METS of numerous activities, and provides a way to look at the intensity or work capacity needed for those activities. When I took the METS results from my test and applied it to the Compendium, I was shocked to see the kinds of activities that are outside my functional capacity.
As I said, my absolute maximum capacity is 5.9 METS. This means I should not attempt any activity over that limit. Examples of activities out of my reach include scrubbing a bathroom with vigorous effort (6.5 METS), moving household items upstairs (9.0 METS), carrying 16-24 pounds up stairs (6.0 METS), or shoveling snow (6.0 METS). Many of the activities are things that I have long since given up on ever doing again, such as hiking (7.8 METS) or swimming slow laps (6.0 METS).
It is more shocking (devastating?) to see the activities over my functional capacity at my anaerobic threshold. On the first test, my AT occurred at a METS of 1.9. This means that any activity over 1.9 METS requires me to rely on anaerobic metabolism. As a result, I can’t sustain those activities for very long and I experience severe and disproportional fatigue afterwards. So I have to be very cautious with those activities, even on non-crash days. What kinds of activities are over the 1.9 limit?
- mild stretching (2.3 METS)
- Hatha yoga (2.5 METS)
- general kitchen activity (3.3 METS)
- light cleaning (2.5 METS)
- washing dishes (2.5 METS)
- cooking, moderate effort (3.5 METS)
- changing bed linens (3.3 METS)
- container gardening (2.3 METS)
- light weeding (3.5 METS)
- playing piano (2.3 METS)
- showering (2.0 METS)
- walking at a slow pace (2.8 METS)
These are basic tasks of living. Some of these I don’t have to attempt (like changing bed linens) because I am fortunate to live with a helpful husband. But if I lived alone? I know so many patients who live alone and have to expend all their energy just doing the basic chores of daily living, and then spend time recovering from them. The METS limit also helps explain why walking at a slow pace has been so difficult for me. I can do it for a short time, but with caution and the risk of crashing. Now I know that it is over my AT limit of 1.9 METS, so OF COURSE it is difficult for me.
Not surprisingly, the activities I spend the most time on are under the 1.9 METS limit. Sitting and watching tv (1.3 METS), reclining while reading (1.3 METS), and knitting (1.3 METS) are all in that safe zone. But as my exercise report noted, when I am crashed my AT occurred at < 1.o METS, which means lying down and doing nothing, or even sleeping, is at or above my limit. The other important thing to note is that METS and the Compendium are both focused on physical activities. I have found no way to measure cognitive load or capacity.
A healthy person spends most of her time under the anaerobic threshold, even while exercising. When she finally crosses her AT, she experiences the rapid onset of fatigue and will stop the activity and rest. And even if she reaches her maximum oxygen consumption and bonks, she will recover to normal within a day or two.
My exercise test shows that my entire energy system is broken all along these stages. I spend most of my time over my anaerobic threshold, except for when I am sitting and reading or knitting. Because I spend so much time over my AT, I have become accustomed, even immune, to increasing fatigue and the signals to stop and recover. And I bonk on a regular basis, without ever approaching my VO2max.
In the last year, I have had to examine all of my activities and modify where I could to try and accommodate these limits. But I don’t live in a world where I can stop washing dishes and cooking and showering. I don’t want to give up slow walking or baking or light gardening just because it is over my AT. Over many months, I have used the heart rate monitor, METS Compendium and a perceived exertion rating of “somewhat hard” to control my physical activity levels. I know it is not practical (or desirable) for me to live below the AT/1.9 METS limit. But I have really struggled to find the right balance between the two extremes of never getting off the couch and cooking/gardening/walking until I bonk. It seems like there should be a big slushy middle ground, but I have struggled to find it.