Choosing a Metabolic Testing Lab: It’s a Jungle Out There


By Uphill Athlete co-founder Scott Johnston

Perhaps you’ve read our articles on fat adaptation Train to Burn Fat , Burn Fat to Go Fast , or What Enables Endurance or the “Getting Tested” series Part 1, Getting Tested and  Part 2, Interpreting Your Results.  If so, you may feel inspired to take the plunge with a lab test of your own. It’d be a great way to start a new training block—by getting some actual personalized data showing your metabolic response to exercise. But where do you go? How do you choose which testing lab to visit? Besides an internet search of available places, what information should you arm yourself with so you are a knowledgeable consumer? And more importantly, why do you need to be informed in the first place? Aren’t all these tests the same?

Let’s start with the last question first: Are all these tests the same? NO!

There are some big differences, which require a little background information to explain.

In case you have not noticed, there is a fitness craze sweeping the nation. Fitness facilities such as gyms and health clubs are popping up like drive-through coffee shops did in the nineties. This boom has coincided with a significant drop in the cost of metabolic testing equipment (called metabolic carts—metcarts—because they used to require a large cart to transport the equipment). This price drop came about due to the miniaturization of the machine and competition among many players in the arena. These metcart companies started marketing heavily to health clubs and gyms because the simplified machines need only a minimally skilled technician to operate them and can represent a significant profit center for the club/gym. In fact, the marketing material of several of these metcart companies drives home the profit center notion in terms of tests/week, the cost/test, and revenue stream to be expected.

The metcarts come with a preprogramed test protocol. All one needs to do is turn it on and off and the machine does the rest. This should be a good thing, right? Technology is making available a test once used only by elite athletes mostly at universities. There’s a hitch, though.

Max VO2 Tests

The fitness industry, along with numerous popular magazines, has done its best to convince us that aerobic endurance can be defined by one number: maxVO2. This number has achieved an undue status as THE gold standard when it comes to endurance. We covered this in our article The Max V02 Myth. But for now, just understand that this is the reason for the recent heavy marketing of maxVO2 tests.

The canned protocol that comes with a metcart is typically a protocol designed to find the maximum oxygen uptake (maxVO2) of a test subject. The protocol for a maxVO2 test is, by its nature, not a good way to test basic aerobic capacity. The typical maxVO2 test ramps up the intensity through an ever-increasing workload, by increasing either the angle of the treadmill, its speed, or both. The problem is the ramp rate. If the subject becomes fatigued during the test, he or she will not achieve maxVO2. To lessen the chance of this happening, maxVO2 tests increase the workload quickly to take you from an easy effort to one that is unsustainable in as short a time as six to ten minutes (it depends on the fitness of the subject). We have reviewed sports club tests with intensity stages as short as 30 seconds, and one-minute stages are not uncommon in maxVO2 tests. On top of the short test itself, we have seen results from a sports club maxVO2 test that allowed only a 30-second warm-up before the metcart started collecting data. A long warm-up is critical to getting decent results.

The reason this test is the wrong choice for finding the important aerobic threshold is that your aerobic system is quite slow to respond to increases in workload (intensity). When you first begin to exercise, the energy comes from anaerobic sources: first from stored ATP, which only lasts for a few seconds, and then from the glycolytic metabolic pathway. Finally, after several minutes, your aerobic system will have come online and begun to provide its share of energy. At each new increase in intensity, it again takes a few minutes for the aerobic system to respond and stabilize. If the intensity (workload) stages are too short, as is common in some maxVO2 tests, your aerobic system does not stabilize in the aerobic zones. It is playing catchup for the entire duration of the test. Consequently, the test results you get from one of these short, rapid ramp-up tests will not provide a realistic picture of how your aerobic metabolism responds to increasing intensities.

A test that will allow you to identify important aerobic markers like aerobic threshold or the percentage of fat versus carbs you use for fuel will have stages lasting at least three minutes; this enables you to attain metabolic equilibrium before the load is increased. You can get a maxVO2 result with these longer staged tests. But the tests take appreciably longer, which means fewer tests per day, which cuts into that revenue stream promised by the metcart manufacture

So what’s an athlete to do?

  • Search for a lab that advertises Metabolic Efficiency Testing (MET). They’ll know what you are looking for.
  • Do this test on a treadmill either walking steeply uphill (climbers and skiers) or running (runners). There will not be much if any difference between the results for these foot born tests.  Don’t do this on a bike unless you plan to do your training on a bike.  
  • If you only find labs offering maxVO2 tests, ask the technician if this test will identify your aerobic Be sure you make it clear: “Aerobic threshold, NOT anaerobic threshold.” About 90 percent of these folks will only be familiar with the anaerobic threshold concept. If they hesitate or ask why you want to know that, then you can immediately cross them off your list.
  • Ask how long each workload stage is. If it is less than two minutes, you know this test won’t work for you.
  • As a last resort ask if you can warm up on another treadmill for 15 minutes before the test.
  • Ask them if they can supply you with the raw data from the test. You can have this evaluated by a knowledgeable coach and we can do it with a phone consultation.

Universities will probably be your best option if you can’t find a MET facility. Universities will likely have kinesiology or exercise physiology grad student lab techs to whom you can ask questions. A good MET test will include at least a several-minute, very gradual warm-up before the test even begins. Our experience with health clubs is that very few know how to administer a test to find the aerobic threshold. Many are not even familiar with the term.

The more you know about these tests, the better the chance of your getting actionable information and your money’s worth.

Be sure to utilize these FREE LAB GUIDELINES to send to your lab of choice ahead of time.


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