Getting Burned with Calories Burned?

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I got this email the other day… wow, I feel kinda special that people think I’d know about this stuff. Remember, I’m not a doctor, and I don’t even play one on TV, so please consult and expert if you want to know the facts.

On 1/11/07, A reader wrote:

Quick question……as I obsessively record numbers (time training, distances, weight, calories) how did you find out your actual calorie burn? Did you have some kind of testing done? I mean, my Polar gives me an estimate based on my settings, but, well, it’s never been validated. Any ideas?

I wish I could give you a simple answer. I admit, I ask myself this same question. Right now, I’m wanting to lose some more weight, but I feel like I have so much else on my plate, that I feel like counting calories is more than I have time for.

I’m not sure how much research you’ve done on this topic, so if this is stuff you already know then please forgive me. It is pretty interesting once you start digging into it… at least I found it interesting. 😉

So with that being said, here are my thoughts on this topic…

Metabolic Testing – I have never done this, but I’ve been told this is the one precise way of determining your daily caloric rate. There are a couple local sports rehab/training clinic near where I live that do this test, along with a couple other tests like measuring your Lactate Threshold and even your VO2max for around $100-$200 depending on how many tests you want done.

If you do this test, you will know for sure how many calories a day you need doing at rest (no activity), and working out at various levels. As I understand the tests, they hook you up to all kinds of medical equipment like EKGs, a Respiratory gas mask, power meters, etc. And measure the gas that you exhale in order to determine what chemical reactions are happening inside your body at certain activity levels. From this they can calculate how your body is actually consuming fuel and oxygen, etc. Very exact, very scientific, IMO, very cool!

I am seriously considering doing this, because I’d like to know how to better train for my next big challenge. I asked my wife to give me this as a Christmas present… but apparently it was too intimidating to even consider. Go figure. 😉

Heart Rate Monitors, etc. – I have used Polar, Garmin, treadmills at the gym, etc. I believe that these report calories based on a concept called Base Metabolic Rate in conjunction with METs or some similar variant. These usually are based on taking your age, gender, height, weight, and other parameters and “estimating” your base metabolic rate. This is an estimate, the test I describe above will give you an exact number.

Here’s one of those formulas for estimating base metabolic rate:

Harris-Benedict formula:

Men: BMR = 66 + (6.23 x “typical” pounds) + (12.7 x inches) – (6.8 x age)
Women: BMR = 655 + (4.35 x “typical” pounds) + (4.7 x inches) – (4.7 x age)

Note: The BMR for women is less dependent on height and weight, which is why the formula for women has a higher constant and which is why BMR is never less than about 1100 calories a day.

Source: John P. Hussman, Ph.D., Hussman Fitness, http://www.hussmanfitness.org/bmrcalc.htm

So for example, for me: male, 37, 5’4″, 140lbs, this results in…

Men: BMR = 66 + (6.23 x 140) + (12.7 x 64) – (6.8 x 37) = 66 + 872.2 + 812.8 – 251.6 = 1499.4

There are other formulas for this estimate, that take different parameters like body fat, etc, and so various formulas come back with a base metabolic rate between 1450 and 1750 for me. In theory, this is how many calories my body needs to simply stay alive and maintain my body structure as is.

Once these algorithms estimate your base metabolic rate, they I suspect that most HRMs and Fitness Equipment will use the concept of METs on a per exercise basis to calculate how much you are burning while doing that exercise. METs are a ratio of your base rate.

Technically METs are (according to Wikipedia):

A unit of metabolic equivalent, or MET, is defined as the number of calories consumed by an organism per minute in an activity relative to the Basal metabolic rate (BMR/RMR, see below). A single unit (1 MET) is the caloric consumption of that organism, or individual, while at complete rest. For example, one might consider the restful state following a quiet night’s sleep as a good example of a single MET. This is a base-line unit for that one individual, and since each individual has a varying BMR, a MET is, therefore, variable from one person to the next. One might consider a single unit the energy required to just stay alive without doing anything more.

Researchers have created catalogs of METs for different activities like walking, running, swimming, cycling, playing soccer, ironing clothes, having sex, you name it. These catalogs are the subject of endless research papers. But they basically boil down to “activity, MET ratio”… so here are some examples I’ve found in some recent published papers…

bicycling-BMX/Mountain; 8.5 MET
bicycling->20mph, racing, not-drafting; 16.0 MET
stretching, hatha yoga; 2.5 MET
running 8mph(7:30min/mile); 13.5 MET
home activity, ironing; 2.3 MET

Now here’s where I think a lot more voodoo happens… In theory, the METs for an activity come from the concept of measuring the chemical reactions from those activities… and so you probably should use your BMR and the METs to determine your actual calories burned during an activity… right? Well, it sounds like most research just says to use the following formula for calories burned during an exercise. (Sources: 1, 2)

Calories = METS x weight (kg) x time (hours)

Why? Well, I guess researches agree that since the MET tables were built using a constant that only included weight of the subjects they were measuring, and the BMR of those subjects may or may not have been utilized in creating the MET tables, you really aren’t getting any more accurate by using your BMR. Or are you? I guess this is the secret sauce that explains why Polar and Garmin and the treadmill at the gym are different. Maybe that’s the technology behind Polars “OwnCal” feature.

Have I lost you yet? Well, if you’re still reading, here’s what I’ve found in practice.

If I go out and ride my bike for 1:15 hours, let’s say I ride at 19.5mph, total distance 24.4 miles

• According to the MET calculations, I should burned: cals = 16.0 * 63.5kg * 2 = 2032.
• According to my Garmin, I burned: 1333 calories
• According to my Polar, I burned: 1250 calories

Ok, so these are all way off from each other… where did the come from? How close to reality are they? Which is most accurate?

I think that Garmin uses a table close to METs… I am sure it doesn’t use Heart Rate at all, because I’ve used it in spin class, where my heart rate is high, but I’m not moving (according to the GPS) and it will read 0 calories burned.

I am pretty sure Polar uses Heart Rate and some proprietary algorithms based on heart rate… I say this because Polar definitely shows lower calories for me if I have a lower heart rate.

The example above was a typical one way commute for me when I would ride my bike to work in the spring/summer… and if I went out and ate an extra 2600 calories per day, I know I would gain weight… but supposedly that’s what even the most conservative of these estimates claimed I was burning doing this exercise.

So what I would do, when I was watching this stuff closely, is use these calorie calculations as an estimate. I would take the most conservative one and then take off another 15-25%. Then I would watch the trend over the long run (say 1-2weeks) and I would see if the calorie deficit I was supposedly creating was really translating into lost weight. A 3500 calorie deficit should translate to 1 lbs of body weight.

As I watched this over the long run, I would “adjust” my BMR and my fudge factor.

Now you can see why I’m interested in doing the metabolic rate test… it sounds like it would actually be easier. 😉

Good luck.