Perhaps you’ve read our articles on fat adaptation—Train to Burn Fat , Burn Fat to Go Fast, and 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 metabolic 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?

For more on aerobic testing, read Aerobic Self-Assessment for Mountain Athletes.

Are 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 haven’t 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 ’90s. 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 per week, cost per test, and the expected revenue stream.

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.

The Problem with 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: max VO2. 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 max VO2 tests.

The canned protocol that comes with a metcart is typically designed to find the maximum oxygen uptake (max VO2) of a test subject. The protocol for a max VO2 test is the best way to test basic aerobic capacity (the low-intensity response to exercise). The typical max VO2 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 max VO2. To lessen the chance of this happening, max VO2 tests often increase the workload quickly to take you from an easy effort to one that is unsustainable in as short a time as 6 to 10 minutes (it depends on the fitness of the subject). We have reviewed fitness center tests with intensity stages as short as 30 seconds, and 1-minute stages are not uncommon. On top of the short test itself, we have seen results from such a max VO2 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.

Why Do You Need a Long Warm-up?

The reason a max VO2 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 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 max VO2 tests, your aerobic system does not have a chance to stabilize. 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 3 minutes. This enables you to attain metabolic equilibrium before the load is increased. You can get a max VO2 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 manufacturer.

Tips for Choosing the Right Testing Lab

• Search for a lab that advertises Metabolic Efficiency Testing (MET). They’ll know what you are looking for.
• Do the 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-borne tests. Don’t do this on a bike unless you plan to do your training on a bike.  
• If you only find labs offering max VO2 tests, ask the technician if this test will identify your Aerobic Threshold. Be sure you make it clear: “Aerobic Threshold, NOT Anaerobic Threshold.” Don’t be surprised if these folks are not familiar with the Aerobic Threshold. 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 3 minutes, you know this test won’t work for you.
• 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. (We can do it with a phone consultation.)

Summary

Universities will probably be your best option if you can’t locate an MET facility. At a university you will likely find kinesiology or exercise physiology grad student lab techs who can field your 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 going in, the better your chance of 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.

-by Uphill Athlete co-founder Scott Johnston