Resting Metabolic Rate Testing (breath test)

Triathlon Forum
1

I recently did one where I breathed into some kind of huge athsema inhaler-looking analyzer and it spat out your resting metabolic rate. Curious to know from those in the field how accurate these are… +/- 10%… 50%?

I fasted all morning, no drinks or caffienne either. A nose clip prevented breathing through the nose and the analyzer would trip an error if it detected a leak around the seal of your mouth - seemingly good controls for a $25 test (company brought them in and may have helped pay for some of the costs).

I am male, 28, active all my life, tris for the last 4 yrs, train yr round, typical 10-15 hr/wk balance with a real job and family, 6’1", 176 lbs, 6-7% BF. i.e. I’m like many of you (only slower). I was surprised to see the resting metabolic rate was 2170!

I think thats a bit high, the RMR is defined as the caloric requirement your body needs if you just woke up and did nothing all day but post on ST. To get the typical day’s caloric requirement (no workouts), a rule of thumb equation took a typical desk job and mult by 1.2 got me up to 2604 cal!!

Add two 1-hr workouts at a very conservative 500-800 cal/hr and I have to eat ~ 3600-4000 just to break even?!?

As I’m scarfing down rice krispie treats like its going out of style, I ask those of you familiar with the test(s), how accurate are these, and how exactly do they work? What is it reading from my breath?

Second data point:
My wife’s test:
26 year old female, active most her life, trains year round, 5-8 hr/wk, 5’1" 115-120 lbs, 20-22% BF

RMR 1600 cal; x 1.2 = 1920 cal

2

Here are some standard numbers to show that this is most likely correct:

the average adult consumes about 0.25-0.3 Litres of oxygen per minute when resting. We can assume 0.3 for you, since you’re about average weight and quite lean (therefore more of the tissues that consume more oxygen). Multiply that by 1440 (~minutes per day) = 432 L/day. Since couch-potatoing can be assumed to be an acitivty that requires essentially 100% aerobically-derived fuels, we can assume that your total energy requirements come from the consumption of this 432L/day. Assuming a ‘mixed’ diet, you need to consume 1L of oxygen to burn about 4.8 calories. Therefore in one day this adds up to 432 x 4.8 = 2074 cal.

Your estimates of energy expenditure during exercise are quite reasonable, but if you have done any tests similar to this one, but while exercising, you can easily calculate energy expenditure during training.

Factoring in that energy expenditure post-training does not immediately fall to resting levels for some time, you might want to factor in a few more cal’s into that final number!! The number crunching is not 100% accurate, there are more factors at play than just energy in and out, exercise time, etc, but not too far off. Your numbers may be surprising, but are true.

3

Thank you for the reply. So the device was measuring the volume of air we moved and from that the amount of O2 in vs. out? (assumed O2% or actually measured?) My engineering mind can see as being very inaccurate while at rest (shallow breathing, some deep breaths or sighs, etc). Although the tester said just breathe normally, at rest I don’t breathe that deeply. I don’t know if its tied into resting heart rate, but my avg 41-45 bpm surely won’t necessitate the need for sucking in more mL of O2 per breath? The same test during exercise I see being more accurate since during training you can’t artificially breathe in/out any deeper/shallower very long to skew the volume of O2 since it would result in labored breathing or starve ourselves of air.
I guess I need to read Lore of Running again, I recall Noakes labored through a lot of this which I skimmed.

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I haven’t done the test. However, I did get nutritional counseling from Monique Ryan, and she felt those were pretty accurate and can be a useful tool for some people. If you aren’t familiar with Monique, she is very athlete-focused nutritionist, and she has a very scientific approach to her practice so I tend to trust her opinion of a test like that.

When I worked with her, she gave me calorie targets based on the formulas suggested above. Then she said that every once in a while there are people who don’t seem to be responding correctly (ie the numbers are too high or too low) and she’ll recommend that test. For me, the numbers she came up with worked fine, so I didn’t do the test.

5

Man…I had that done at my gym for over $100 included was some other tests though. Sounds like the same equipment.

My number was 1990. My plan was been to hit that number everyday regardless of workout. I’ve dropped 10lbs since middle-late January. Once I start the long rides/runs I’ll change that but so far so good…

6

So the device was measuring the volume of air we moved and from that the amount of O2 in vs. out? (assumed O2% or actually measured?)

Pretty much. Basically the machinery you are hooked up to measures the volume of air that you expire, and the concentration of O2 and CO2 in it. You already know the O2 and CO2 of the air going in (ie room/atmospheric air), and a simple calculation is used to work out the inspired air volume. The rest is a few more simple calcs to work out VO2 (rate of oxygen consumption in your body), which is the value I mentioned before. They would also likely use the VCO2 as well to make the calculations a little more useful and accurate.

My engineering mind can see as being very inaccurate while at rest (shallow breathing, some deep breaths or sighs, etc). Although the tester said just breathe normally, at rest I don’t breathe that deeply. I don’t know if its tied into resting heart rate, but my avg 41-45 bpm surely won’t necessitate the need for sucking in more mL of O2 per breath? The same test during exercise I see being more accurate since during training you can’t artificially breathe in/out any deeper/shallower very long to skew the volume of O2 since it would result in labored breathing or starve ourselves of air.

Your engineering mind has given you great skills of deduction! These tests are notoriously inaccurate at rest, mainly due to anxiety, and simply being hooked up to all the gear, causing altered breathing patterns. Problems are very easy to see, as long as the test is “on line”, ie giving instantaneous feedback. Over a long period the data tends to smooth out and breathing normalises, so as long as the measures are taken over a long period and you are given adequate familiarization, then the numbers should be fine. You are also correct that the numbers are more accurate during exercise. Exercise is a great “equalizer” from this respect. The altered neural and hormonal output over-rides any anxiety, etc related discrepant breathing patterns and so on.

I guess I need to read Lore of Running again, I recall Noakes labored through a lot of this which I skimmed.

Tim Noakes is a clued-up guy. Certainly wouldn’t hurt to flick through again if you want to brush up, but there are probably more basic textbooks you could find…