Getting your 'fat burning' tested Part 1:
Equipment and protocol
Alan Couzens, MS (Sports Science)
Feb 29th, 2016
Above: The tables are turned - pro triathlete Justin Daerr checking the numbers on a metabolic test for yours truly. Note the unimpressed facial expression :-)
Thanks to my good friend, Tawnee Prazak, of Endurance Planet, I recently had the incredible opportunity to do a podcast with one of my long term idols in the applied exercise physiology game, Dr. Phil Maffetone on a subject that has been an obsession for most of my post-collegiate life – metabolic fitness or, ‘fat burning’.
Specifically, the conversation was centered around the value of metabolic testing for endurance athletes. As someone who has spent the better part of the last decade performing & analyzing these tests, you don’t get a prize for guessing on which side of the fence I sit :-)
My take, after testing a wide range of athletes of different abilities and specialties, is that events longer than ~2hrs duration are metabolically limited rather than fitness limited...
... i.e. irrespective of how 'fit' you are & how much aerobic power you may have, it is your aerobic capacity for generating high levels of energy over a very long time that truly makes the competitive difference. This has been shown time and again in the Ironman athletes that I've tested from the 'pointy end' of the field. VO2max values are good but often not spectacular. It is the fat oxidation numbers that truly shine. So, when testing performance-oriented long duration athletes, it is this quality that we want to track
This area of physiological strength makes a lot of sense. Considering that even the leanest athlete has over 50,000kcal(!) of energy on board as fat & only 2-3,000 as carbohydrate, a large part of our overall long term capacity to ‘do work’ comes down to how strong our proverbial factories are in burning that fat store to help fuel our race specific energy needs.
From an assessment perspective, the tricky thing about fat burning is that it is very difficult to assess in the field. Short of actually going out and seeing how long it takes you to completely deplete your energy stores, you're not going to know if, in an exercise context, your fat burning is good or bad.
So, we have a physiological quality that is very important to our event and practically impossible to assess in the field. What do we do? To the lab! :-)
The only really feasible way (in a manner not disruptive to training) to assess this metabolic fitness is with semi-regular fat oxidation tests in the lab. In these tests we use a gas analyzer to test your ‘exhaust fumes’ to see just what percentage of your energy burn is coming from fat & CHO at different intensities. This type of lab testing (an aerobic capacity test) is different from the more traditional aerobic power VO2max or lactate testing that most athletes go into the lab for but it is a far more applicable test for athletes with a 90 min+ event. However, this type of testing is far less prevalent and less popular in commercial exercise physiology labs for a number of reasons….
One key reason is that a proper metabolic test from start to finish takes a long time. If you factor in setting up the equipment, properly calibrating the machine, properly warming up the athlete, performing the test, thorough cleaning of the equipment (!), downloading, analyzing and interpreting the results, you’re looking at a good 6 hours of work for one test! It is not coincidental that I have significantly scaled back my own testing practice to focus only on my own athletes and certain 'special projects' :-) But what I'd like to do in this post is to use my experience to empower you to get your own high quality, event specific test data by offering a protocol that you can take to your local lab to ensure that you’re getting a valid & reliable test that is specific to the demands of your event….
So, without further ado, what are the key points that we need to observe if we’re interested in getting high quality results from a fat burning test?
A good quality metabolic cart – a unit that can keep up with the air flow rates of competitive athletes is expensive. Far too expensive to make the budget cut for most health clubs. In other words, when you see that your local health club offers “VO2max testing”, if your VO2max is north of 3L/min, they’re probably not talking to you.
For medium-high level athletes, your best bet in finding good equipment (that can handle your flow rates) is to check in with your local university. Almost all exercise physiology programs will have a high quality metabolic cart (Parvomedics, Sensormedics etc) as a standard piece of kit & lucky for you, it’s typically an under-utilized piece of equipment! Once the course content on VO2max testing is done, it hangs out in the corner of the lab. Let’s put it to work!
OK, so you contact your local university. The conversation will go a little something like this…
“Do you have a metabolic cart?”
“Yes. Would you like to book in for a VO2max test?”
“No. I’d like to book in for a metabolic test”
“You mean a VO2max test?”
Repeat ad infinitum.
The most significant difference between VO2max & fat oxidation testing (that you'll want to get across) comes down to protocol.
The test protocols for VO2max and fat oxidation differ in stage number and duration, i.e. the test that you're asking for is going to start easier & take longer. Once you get this across, this additional time is generally less of a problem for a university than it would be for a commercial lab...
See, here’s the thing about universities: While they tend to stick with what they know, they are also full of insatiably curious folks like myself who are always up for a bit of experimentation &, to add, these insatiably curious folk have minions that they can recruit to do all the unpleasant stuff associated with these experiments without, or for very little pay. What a glorious set up! :-)
Long way of saying - go in with your own protocol! Generally, if you go in with a purpose of what information you're looking to get and a specific, predetermined protocol to go along with it ("My coach says he wants me to do this test"), you can often find a curious soul willing to run it.
So, what are the nitty gritty details of the fat oxidation protocol that you want to execute?
First up, it is important that the test is done in at least a semi-fasted state so that you’re not getting a recent blood glucose spike artificially increasing the numbers. I recommend fasting 3hrs prior. So, you may plan a 10 am test, get up around 6, eat (& record) your normal breakfast then not eat anything (or drink anything with sugar in it) prior to testing.
Next to work out the stages, or 'steps' in the test, you’ll need a rough estimate of your FTP. Doesn’t have to be precise, just enough to get you in the ball park. Plug that in below and the calculator will spit out some recommendations on power numbers for each stage of the test.
Approx run FTP (km/h):
Warm up: 30min @
Super important to make sure we're starting from a true baseline! You don’t need to wear the mask/collect data for the warm up. Following the warm up, get a baseline lactate reading to make sure that the intensity was sufficiently low (we are looking for <1.5mmol/L). If not, reduce the intensity and continue to spin easily for another 15. Then put on the head-gear and begin the test...
|Stage||Duration (min)||Time (min from test start)||Power (W)|
Some additional points
- While a max target is given, I recommend going to failure on the bike & to a safe max on the run. This may occur at stage 8 or 9, or you may exceed the planned 10th stage and move into stage 11.
- Ideally you will also get a lactate sample at the end of each stage.
- Following the test, it is important to cool down at a very low output for 20-30min. If keen, you can also lactate sample during this time at 2,5,10,20min to get a lactate recovery curve.
You can expect to pay somewhere in the $300-$400 range for a high quality test. In my opinion, a bargain for the time involved and the cost of the equipment. And remember, someone has to clean out your spit tube! :-)
i.e. How often do I need to do this?
This depends a little on what you find out, i.e. does your fat burning need to be improved? I’ll look at answering this qu with some thoughts on interpreting the test in my next post but if so, I would recommend 2-3 tests per year. If not, this may be something that you just check in on, on an annual or bi-annual basis to see if anything is changing in a negative direction, with at home lactate tests using a (much more cost effective) portable analyzer, making up the balance of your testing through the year.
In my next post I’ll look at what numbers you’ll get, I’ll offer a calculator that will give you a nice visual representation of your own fat burning once you have your data & I’ll give some norms that I have seen from my years of testing different levels of athlete that you can compare it to. But for now, your homework is to book your test.