Huge discrepancy with BodyBugg vs. Polar FT4

summertime_girl · February 2012

I've been using a BodyBugg for a little over a year to track calories burned. I wear it pretty much all day, but do not sleep in it (beyond the first week I had it to get the full BMR).

I just bought a Polar FT4 to do some HR zone training, and today was the first time I've used it. For a one hour workout comprised of two miles of running (22 minutes), P90X chest/shoulders (35 minutes), and elliptical cool down (5 minutes), the Polar said I burned 724 calories. I kept my heart rate in the zone or above for the full hour.

The BodyBugg said I burned 520 for the same time period.

I've searched in Google and these forums, and I see a lot of discussion about the two gadgets, but all seem based on opinion. I'd love to find a scientific study that says one way or another which is more accurate. Has anyone come across anything?

SavCal71 · February 2012

is the BodyBugg possibly subtracting your BMR already? So, maybe you did burn 720ish, but you would have burned 200ish without the exercise, so BodyBugg adjusts for that?

I'm just throwing out ideas ...

chickybuns · February 2012

I have a bodybugg, and I would go with the lower number, as it's worse to over rather than underestimate. I also agree with the previous poster, maybe the BB takes out normal burn from the equation.

summertime_girl · February 2012

BodyBugg definitely doesn't take out the BMR. It shows a graph for the whole day when sync'd, and the calories burned per minute go up when exercising.

I like the idea of using the lower number, but then I worry I'm not eating enough back, if I'm potentially burning hundreds more calories per workout. I need to find something scientific one way or another.

summertime_girl · February 2012

Bump....anyone?

Google has uncovered nothing. I'm leaning towards the HRM being more accurate, simply because it takes into account heart rate, which the BodyBugg does not.

BodyBugg measures the following:
• Motion: The armband contains an accelerometer that measures motion from multiple perspectives.
• Steps: The accelerometer counts steps by measuring the distinct patterns created by running or walking.
• Galvanic skin response: When you sweat, your skin becomes more electrically conductive. This measurement helps the device understand how active you are.
• Skin temperature: There’s an electronic thermometer inside your armband that monitors how hot you are.
• Heat flux: When you move, your muscles produce heat. Your armband measures the heat that’s flowing from your body into the environment.

Since calories burned is more closely correlated to heart rate (dependent on how much oxygen in vs. carbon dioxide out, with mathematic estimates for determining HR to breaths taken), it seems likely that the HRM may be more accurate than temperature or motion. But I can find nothing except opinion either way.

crossfitterwahine · February 2012

I would go with the heart rate. You want your heart rate in a certain zone anyway during your various workouts, right? I think there is a danger of underestimating by that much, everytime you workout.

wolfchild59 · February 2012

I have a Polar FT4 and a BodyMedia Fit. I would say, based on my experience, that your answer lies somewhere in between.

The BodyBugg, since motion is a big part, won't always record things like the elliptical, an ARC trainer, roller skating, or biking properly because your arms aren't engaged in the same way as other activities. Yes, there is a level of engagement with them, but it's still different.

But the HRM is probably going to over estimate a bit for strength building period of time. An HRM bases calories burned off of an elevated heart rate. And while lifting during a workout does elevate the heart rate, you're not getting the same caloric burn as full-on cardio. (that's why strength alone in MFP doesn't allot calories for strength).

So you're likely getting a combo of underestimation from the BB for the elliptical, and then some overestimation from the HRM for the strength parts of your workout DVD.

wolfchild59 · February 2012

Oh, and here's the info I was paraphrasing on the HRM and strength training, as back up:

A HRM won't give you an accurate idea of how many calories you burn during strength training, because the relationship between heart rate and calorie expenditure is not the same during strength training as during cardio exercise, which is what the HRM's estimate is based on. Unless your weight training is very vigorous circuit training, the heart rate monitor will be overestimating your calorie burn by a fair amount.

The problem is a technical one. Calorie burning isn't determined by heart rate, it's determined by the number of muscle cells that are activated to perform a given activity. It's the working cells that actually use the energy (calories) and consume oxygen. When working muscle cells need more energy and oxygen, your heart rate goes up to deliver these things to the cells via the blood stream.

Any muscle that performs a high intensity or maximum effort (strength training) will trigger an increase in heart rate and blood flow. But if only a single muscle group is on the receiving end to utilize that extra oxygen (doing a strength exercise that isolates your biceps, for example), only a relatively small amount of oxygen (and calories) will actually be consumed.

So while a series of strength training exercises may elevate your heart rate like aerobic exercise does, you're not actually using as much oxygen and burning as many calories as you would be if you were steadily using several large muscles all at once, as when walking, running, swimming, or doing aerobics for example.

The heart rate monitor doesn’t know whether your increase in heart rate is due to several large muscle groups working (cardio), an isolated muscle group lifting a weight (strength training), or even if adrenaline or excitement is increasing your heart rate. It just knows your heart rate, and the formulas it uses to estimate calories are based on studies of aerobic exercise, not other activities. So, it's going to overestimate your calorie expenditure when the rise in heart rate is stimulated by using isolated muscles at maximum intensity, which is what occurs during strength training.

Written by Dean Anderson, Certified Personal Trainer

Azdak · February 2012

Oh, and here's the info I was paraphrasing on the HRM and strength training, as back up:

A HRM won't give you an accurate idea of how many calories you burn during strength training, because the relationship between heart rate and calorie expenditure is not the same during strength training as during cardio exercise, which is what the HRM's estimate is based on. Unless your weight training is very vigorous circuit training, the heart rate monitor will be overestimating your calorie burn by a fair amount.

The problem is a technical one. Calorie burning isn't determined by heart rate, it's determined by the number of muscle cells that are activated to perform a given activity. It's the working cells that actually use the energy (calories) and consume oxygen. When working muscle cells need more energy and oxygen, your heart rate goes up to deliver these things to the cells via the blood stream.

Any muscle that performs a high intensity or maximum effort (strength training) will trigger an increase in heart rate and blood flow. But if only a single muscle group is on the receiving end to utilize that extra oxygen (doing a strength exercise that isolates your biceps, for example), only a relatively small amount of oxygen (and calories) will actually be consumed.

So while a series of strength training exercises may elevate your heart rate like aerobic exercise does, you're not actually using as much oxygen and burning as many calories as you would be if you were steadily using several large muscles all at once, as when walking, running, swimming, or doing aerobics for example.

The heart rate monitor doesn’t know whether your increase in heart rate is due to several large muscle groups working (cardio), an isolated muscle group lifting a weight (strength training), or even if adrenaline or excitement is increasing your heart rate. It just knows your heart rate, and the formulas it uses to estimate calories are based on studies of aerobic exercise, not other activities. So, it's going to overestimate your calorie expenditure when the rise in heart rate is stimulated by using isolated muscles at maximum intensity, which is what occurs during strength training.

Written by Dean Anderson, Certified Personal Trainer

The overall effect (overestimation of calorie burn) is correct, but the explanation sounds like something he just made up--or plagiarized from another Internet article (same thing).

The discrepancy with heart rate and oxygen uptake (calories) results from the different physiological mechanisms involved. During aerobic exercise, the increase in heart rate is accompanied by an increase in cardiac output, therefore in increase in oxygen uptake. During resistance exercise, the increased heart rate is due to increased pressure, and there is not a corresponding increase in cardiac output. Therefore, oxygen uptake does not increase--at least not directly.

To the OP: I suspect the "in between" answer is correct. The BB is underestimating and the Polar is likely overestimating overall.

taso42 · February 2012

It's all a guessing game really. Just log everything in a consistent manner and with a trial and error you can eventually dial it all in by fine-tuning your daily calorie target.

_GlaDOS_ · February 2012

It's simple, really. A HRM is using one method of determining energy expenditure, while a bodybugg is using like 6 different modalities. Heart rate can be affected by many different things - stress, medication, other psychological factors, etc, but you don't really burn many more calories when you're stressed or on medication that increases your heart rate.

Scott613 · February 2012

Add them up divide by 2 and use that number...... You burned 622 calories:flowerforyou:

adhillman01 · March 2012

Oh, and here's the info I was paraphrasing on the HRM and strength training, as back up:

A HRM won't give you an accurate idea of how many calories you burn during strength training, because the relationship between heart rate and calorie expenditure is not the same during strength training as during cardio exercise, which is what the HRM's estimate is based on. Unless your weight training is very vigorous circuit training, the heart rate monitor will be overestimating your calorie burn by a fair amount.

The problem is a technical one. Calorie burning isn't determined by heart rate, it's determined by the number of muscle cells that are activated to perform a given activity. It's the working cells that actually use the energy (calories) and consume oxygen. When working muscle cells need more energy and oxygen, your heart rate goes up to deliver these things to the cells via the blood stream.

Any muscle that performs a high intensity or maximum effort (strength training) will trigger an increase in heart rate and blood flow. But if only a single muscle group is on the receiving end to utilize that extra oxygen (doing a strength exercise that isolates your biceps, for example), only a relatively small amount of oxygen (and calories) will actually be consumed.

So while a series of strength training exercises may elevate your heart rate like aerobic exercise does, you're not actually using as much oxygen and burning as many calories as you would be if you were steadily using several large muscles all at once, as when walking, running, swimming, or doing aerobics for example.

The heart rate monitor doesn’t know whether your increase in heart rate is due to several large muscle groups working (cardio), an isolated muscle group lifting a weight (strength training), or even if adrenaline or excitement is increasing your heart rate. It just knows your heart rate, and the formulas it uses to estimate calories are based on studies of aerobic exercise, not other activities. So, it's going to overestimate your calorie expenditure when the rise in heart rate is stimulated by using isolated muscles at maximum intensity, which is what occurs during strength training.

Written by Dean Anderson, Certified Personal Trainer

The overall effect (overestimation of calorie burn) is correct, but the explanation sounds like something he just made up--or plagiarized from another Internet article (same thing).

The discrepancy with heart rate and oxygen uptake (calories) results from the different physiological mechanisms involved. During aerobic exercise, the increase in heart rate is accompanied by an increase in cardiac output, therefore in increase in oxygen uptake. During resistance exercise, the increased heart rate is due to increased pressure, and there is not a corresponding increase in cardiac output. Therefore, oxygen uptake does not increase--at least not directly.

To the OP: I suspect the "in between" answer is correct. The BB is underestimating and the Polar is likely overestimating overall.

By definition Cardiac Output equals the Heart rate times Stroke Volume (CO= HR X SV). The only way for the cardiac output not to increase with increased heart rate is for stroke volume to decrease. What about strength training causes a decrease in stroke volume?

mawright1231 · January 2014

I've noticed anywhere between a 300-500 calorie discrepancy between my bodybugg and my heart rate monitor. What I've done is just average the two and use that as my calories burned during my workout.

Huge discrepancy with BodyBugg vs. Polar FT4

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