Tuesday, May 31, 2011

The Bruce Protocol

If your doctor ever suggests that you need to have a 'stress test' to check on your heart, it is very likely that you will end up on a treadmill, hooked up to many wires and tubes. Someone will be there monitoring your every heartbeat and documenting your response to the exercise.

The most commonly used protocol is called the Bruce. According to Wikipedia, it was developed by Robert Bruce, as an attempt to standardize the measurement of responses to exercise. You may be interested to know, however, that these tests usually do not require any running (most patients stop before stage 4). The speed and elevation of the treadmill follows a precise protocol, which, for Bruce, starts with walking at 1.7 miles per hour and 10% grade.

The purpose of this test, of course, is to test people who are having symptoms like chest pain and shortness of breath. Aside from that, though, it can be used as a surrogate for estimating VO2 max (maximal oxygen consumption). This, in turn, is a measure of cardiovascular fitness because it represents how much oxygen you are able to consume and transfer to your muscles to burn in aerobic exertion. The ideal way of measuring VO2 max is by directly measuring how much oxygen you inhale and exhale during exertion, but if you have access to a treadmill and can run the Bruce, there are calculations for estimating your VO2 max.

So, last month, after the marathon I figured I would give it a shot. Obviously, the first three stages or so were just a walk, an uphill walk, but nothing challenging. The next couple of stages actually were quite awkward because they are in that speed where it feels very weird to walk that fast, but it is not quite fast enough to run. By the time I got to stage 6, I was definitely running the entire time and it was very challenging. I was seriously sucking wind, but my legs were not that tired, which is the purpose of the test after all. 

While this is meant as a test of maximal exertion, clearly you have to recognize when you think you are at 99% so that someone else can shut off the treadmill. This can be hard, because you can imagine that you could always go another 5, 10, maybe 15 seconds more. When I got in sight of 24 minutes though, I figured that would be a nice even number and I was barely able to get enough air to tell someone to shut it off for me, so I figure that is pretty close to maximal. 

So, with a 24 minute run on the Bruce, my VO2 max is estimated at 75! Somehow I kind of doubt that actually, seeing as how Lance Armstrong's is reported somewhere in the 80's. Also, for the Bruce protocol programmed at my hospital, the speed and elevation are fixed after stage seven, where the true maximal test continues to increase. The calculators I found expect the true maximal test, so they are probably an overestimation.

There are some other estimates of VO2 max which do not require a treadmill:
  • Cooper test: Take the distance you can run in 12 minutes (for me, about 2 miles or 3,218 meters) subtract 500 and divide by 45. This estimates my VO2 max at 60.2.
  • Pedersen estimate: Take your max exertional HR (195), divide by your resting HR (55), and multiply by 15. My estimate is 53.2.

No comments:

Post a Comment