Why Metabolic Testing?

Raise your hand if you’re an endurance athlete who gets frustrated by one of the following: not losing weight despite training a lot; struggling to keep your heart rate/breathing/fatigue in control while running uphill; bonking during every long run; etc. Is your hand up? You’re in good company. Endurance activity at its core is about using fuel in the body to do work. Do it well and you’ll go farther and faster with less effort. But miss the mark and you’re lying in a blubbering heap, with visions of cheeseburgers bobbing down the trail in front of you. Chances are, most (probably all) of us have been there before.

Anytime you start a new training season, getting some baseline data eliminates the guesswork of where training zones are, and provides valuable information. We encourage athletes, regardless of goals, to get set up with metabolic testing. It’s not as invasive as it sounds: the basic idea is to determine what’s going on “under the hood” when you’re exercising – how your body uses fuels (carbs or fats, usually), in what ratios and how efficiently? With that information, you can be sure that you’re training within the most effective parameters to achieve your specific objectives.

How does it work? Strap a rubber hose and mask to your face and run for 20-30 minutes on a treadmill-sound like fun? There are several different protocols for metabolic testing that typically involve a stationary modality such as a treadmill or spin bike, a system of hoses, a mask, and computers to analyze the oxygen you breathe and the carbon dioxide you exhale during a specific exercise protocol. For decades, a version of this test was used to determine an individual’s maximal oxygen uptake (VO2 max). But over the years, coaches and physiologists have downplayed the importance of max VO2 as a measure of success in competition and instead focus on understanding the value of the data gathered en route to that maximal effort.


Ideally you burn fat for the majority of endurance activity. Your body uses carbohydrates (in the form of glycogen) as well, but reserve them for very high intensities where quickly-sourced energy comes in handy. Fat is more plentiful (even with very lean athletes) and using it results in fewer negative by-products and fatigue. Undergoing a metabolic testing protocol that takes you up to about 80-90% of your max output can illustrate accurately how much fat and carbohydrate is being burned at varying intensities. Working with a coach, this information helps determine where to focus your training energies, how you might adjust diet to support endurance, and what your overall “efficiency” is. These data points are also correlated with heart rate and as pace, so you have multiple metrics to use.

Most athletes train too hard on easy days, limiting aerobic gains and accumulating fatigue which prevents effective hard training later. Knowing your actual output and heart rates to use supports the ability to get through long runs without a bonk, and in the process, build a strong aerobic base, allowing you to go farther and faster, with less effort.

Metabolic testing is increasingly available in most cities; in Seattle, check out Real Rehab in Northgate – they have multiple methods for conducting the test and really know their stuff.