Facts about aerobic exercise and calories

Azdak

I just saw another infomercial this morning about how you can "burn up to 800 calories in 30 minutes" (unlikely, unless you set yourself on fire), and felt compelled to post some actual facts concerning calories and exercise.

Many of you may already know this, but it never hurts to restate the basics. I am going to address calories burned during aerobic-type activities only, since strength training is much more variable.

Basic fact: the amount of calories you burn during exercise is a product of:

Intensity x body weight.

That's pretty much it. The harder you work or the heavier you are, the more calories you will burn per unit of time.

Aerobic intensity is measured directly by the amount of oxygen consumed during the activity (again, per unit of time). The higher the intensity, the more oxygen consumed. Heart rate is an *indirect* measure of intensity--we use it because it is more convenient and because, in general, during aerobic exercise, heart rate changes reflect changes in oxygen uptake.

Oxygen uptake (VO2) is usually expressed in terms of milliliters of oxygen consumed per kilogram of body weight per minute, or VO2 = ml/kg/min. As a convenience, oxygen uptake is often expressed at METS. One MET represents the estimated energy expenditure at rest, or 3.5 ml/kg/min. METS are used because the numbers are simpler to read --e.g. it is easier to compare 5 METS to 8 METS than 16.5 ml/kg/min to 28 ml/kg/min.

To calculate "calories per hour" for an activity, multiply Intensity (in METS) times Body Weight (in kg). Example, a 70 kg individual running 6.0 mph on level ground will burn approx 714 calories per hour (10.2 METS x 70 kg).

Any claim that "X Machine" or "Y Activity" will "burn more calories" than some other machine or activity is fundamentally false--those making the comparisons are not comparing apples to apples. The intensities are not the same. Theoretically, if aerobic intensity is the same, one should burn an equivalent number of calories regardless of the activity. Practically, it is more comfortable to work at higher intensities at some activities than others. For example, running and elliptical trainers tend to "feel" easier at higher intensities than, say, stationary cycling, so most people tend to burn more calories at those activities. If an infomercial for the Nordic Track Incline Trainer claims that you are burning "twice as many calories as walking on a normal treadmill", it's because the comparison workload is twice as hard--there is nothing "magic" about the incline trainer.

There is also nothing magic about a heart rate monitor that calculates calories burned. Polar HRMs are using proprietary algorithms to calculate calorie expenditure based on HR response to exercise--they are not directly measuring anything. Because of the different variables involved, regardless of the claims by Polar, I would estimate the accuracy of the calorie counts as being plus or minus about 15%-20%. You have to really make sure you have the parameters set up properly (age, weight, HR max, est VO2 max).

Intensity is only one part of the equation when using exercise for weight loss. The other is total calories burned per workout/day, or duration. If you have the time, you can accumulate a significant calorie deficit without having to work at a fitness training intensity. Walking 4 miles in an hour will burn approximately 400 calories, even if your heart rate doesn't go above 100. So working harder is not necessarily the only solution.

If you can tolerate a training threshold, then you get the benefits of both worlds--increased calorie expenditure AND increased fitness.

One of the biggest mistakes I see is that people overestimate the intensity and thus the calorie expenditure of their activities. They mistake muscle fatigue for intensity. Often, when trying a new activity, one is going to feel fatigued more quickly, or uncoordinated, or have general perceptions of higher exertion than what is actually occurring. This is especially true in exercise classes. Once one develops a level of familiarity with the movements, intensity can drop way down. I have been watching some classes on Fit TV lately, and have looked at some of the Jillian Michaels stuff, and, quite frankly, the overall intensity seems modest at best--in the 4-7 MET range. The more fit you become, the more important it is to maintain a focus in these classes and doing things to keep the intensity up--raising a step, moving through a wider range of motion, more energetic movements, etc.

queen3510

Great information! Thank you for posting!

CarmenSantiago

WOW!! Thank you so much for posting this. Very interesting and informative!

arewethereyet

Thanks!!

nightangelstars

Very good information, thanks! This matches a study I read recently that showed at the same RPE (rate of perceived exertion) running had higher VO2 and higher heartrates than graded walking (which is walking uphill on a treadmill). Thus for feeling like you're doing the same amount of work, you can burn more calories jogging - which is useful information to know, if you're trying to choose between those two activities.

Thanks again! :flowerforyou:

135gratitude

Hahahaha - I like the part about lighting yourself on fire!!!

This is a great post - a great reminder to those of us who are working out with weight to lose - those excess pounds work FOR YOU!! It's like carrying extra weights in your hands during a workout!

GlamNGlitter

maybe i'm just reading it wrong or slow to the whole MET (math/science was never my forte') thing but how do I calculate my MET so i can calculate the rest.

Juicey1401

Bumped for later read.

gemiwing

I needed to see this today- I've been secretly jonesing for that new Nordic Track treadmill thing.

I can dance around my house for free

Kityngirl

Great information, thanks for posting! :happy:

dskline1

bump for reading later....

Azdak

I needed to see this today- I've been secretly jonesing for that new Nordic Track treadmill thing.

I can dance around my house for free

True--although there is nothing wrong w/the Nordic Track if you want to focus on incline walking. There is just nothing magic about it--it's a machine that has a higher incline than the average treadmill.

Actually, incline walking can be a good way for a less fit person or someone who can't jog to ramp up their calorie expenditure. I do it sometimes myself when I just want to bang out some calories by walking for an hour while watching TV or something. I can burn more calories walking relatively slow (2.6-2.8 mph) up a 10%-13% incline than I can trying to walk briskly (4.0 mph) up a moderate incline (4% or so), and it's a lot more comfortable.

You just have to make sure that: A) you think incline walking is something you want to do and you don't hold on (which negates the whole "intensity" idea). You might be able to do the same thing w/ regular treadmill. NT products tend to be a little overpriced. Also, there's some overkill--the thing goes to a 40% incline, which is way more that you need--even 20% is going to be very difficult for many people. Then if you decide you ever wanted to walk faster, or run, the length looks a little short.

Azdak

maybe i'm just reading it wrong or slow to the whole MET (math/science was never my forte') thing but how do I calculate my MET so i can calculate the rest.

The article was getting long, so I really didn't get into that. Aerobic intensity (METS) is measured by directly measuring oxygen uptake (unavailable for the avg person) or using tables or formulae to estimate.

Activities like walking, running, stationary cycling, stairclimbing, have well-established formulae to calculate energy expenditure. Other activities have been measured in a lab and published in tables--I'm sure a lot of the info is located on the web. The trickiest thing is trying to estimate intensity for intermittent or stop-and-go activities like exercise classes. In this situation, the Polar HRMs, flawed as they are, are probably the best tool available.

Azdak

Very good information, thanks! This matches a study I read recently that showed at the same RPE (rate of perceived exertion) running had higher VO2 and higher heartrates than graded walking (which is walking uphill on a treadmill). Thus for feeling like you're doing the same amount of work, you can burn more calories jogging - which is useful information to know, if you're trying to choose between those two activities.

Thanks again! :flowerforyou:

There was a similar study (maybe the same one) that compared different modalities -- treadmill, stairclimber, elliptical, bike, rower--the same way. The conclusion was that the treadmill burned the most calories for any given RPE, but what the study never mentioned was that subjects were RUNNING on the treadmill--it was not the treadmill per se, but the activity. You had to look at the raw data (i.e. the VO2 max of the subjects) to realize that the only way they could have reached the RPE levels described in the study was by running.

Running is a great weight-loss exercise (as well as building fitness) precisely because it is inherently a high-intensity activity. Even running fairly slowly is pretty intense compared to many other exercise activities. Because of the high-intensity and the high-impact, running is not for everyone, however.

Anything that gets both feet off the ground at the same time is going to be a higher intensity movement--running, jumping rope. jumping jacks, hop steps. If you are doing a class or a video and need to put some extra oomph into the routine, you can try to add these elements to give it a boost.

Schaff

Terrific post! It just affirms the theory that when you workout, wherever you do and whatever you do, you should be making your workout as efficient as possible. Posts like this help us understand how to get to that maximum efficiency point to become the fittest, and slim-est, you!