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polar Heart rate monitor Calories burned accurate??

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polar Heart rate monitor Calories burned accurate??

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Old 09-05-08, 06:46 AM
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Smallguy
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polar Heart rate monitor Calories burned accurate??

I've been using my heat rate monitor more and more on rides on and off road because I had a suspicion (SP) that my perceived effort and my real world effort were not the same.

anyways I'm 5'10 and 215 pound and over a 2.5 hour ride I apparently burned about 1500 calories

does this seem logical??

I'm not really sure on the accuracy because muscle burns more calories than fat per pound so how does polar accurately calculate or is it not accurate at all?

my goal is to continue to continue dropping weight and get to about 190-200
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Old 09-05-08, 09:42 AM
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telebianchi
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I first starting using a Polar HRM just over a year ago. From reading through various sources -- some scientific and some anecdotal, I came to the opinion that the calorie counter of the Polar is slightly optimistic. (In general this has to do with using the heart rate to calculate calories is not a direct equation. Heart rate can be used for a reasonable estimation of calories and then the HRM uses algorithms to including the heart rate, user's weight and age to calculate the calories burned.)

What I've ended up doing is to set my weight in the HRM about 5 lbs below what my actual weight is. Also, at the end of a ride or other activity I round down the calories burned when entering them into FitDay. So if the HRM says I burned 650 cals, I'll enter 550. HRM says 2300, I'll enter 2000.

I know that what I enter for calories burned may not be 100% accurate, but then I doubt that my calories eaten are 100% accurate either. And over the course of several weeks these things probably equal out. What I do know is that by using this method I was able to drop a consistent 5 lbs a month over 6 months.

Originally Posted by smallguy
anyways I'm 5'10 and 215 pound and over a 2.5 hour ride I apparently burned about 1500 calories

does this seem logical??
There is actually no way to answer this because we don't know what distance you went, flat terrain or a lot of climbing, what condition you are in, what your heart rate or perceived effort was. As an example, I can do a 2 hour ride where my HRM says I used up 800 calories. Two days later I can ride for two hours a lot harder on different roads and get 1250 calories on the HRM. Both numbers being relatively accurate (see my first paragraph) based on my effort during those rides.
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Old 09-05-08, 10:02 AM
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thank you that was what I was thinking

the terrain we covered was steep and technical at points with long climbs in sections

the monitor is doing what I want though and letting me know how hard I really am working instead of how hard i think I'm working
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Old 09-05-08, 01:18 PM
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HRMs are very good at measuring HR - and nothing else. - TF
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Old 09-05-08, 06:48 PM
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The Polar estimates about 30% high for me, compared to a real power meter (I have a polar and a powertap).

Since the polar can't measure your power (assuming you don't have the power meter attachment), it uses a formula based on your weight and HR and HRmax. That's not very accurate, and always seems to be high.
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Old 09-05-08, 06:50 PM
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I switched from using a HRM to a power meter. The calories burned for my usual routes were about 30% less according to my power meter.

Let's not even get into how far off calorie counters on gym equipment are....
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Old 09-05-08, 08:29 PM
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I don't know what a power meter is, but the last time I rode 2.5 hours I covered 58 km. According to my low-budget cycling computer which judges calories burned based on age, velocity, time, and weight that trip burned ~3300 kcal (it also suggests 0.85 lbs of fat burned, but obviously not every calorie burned came from fat). The calculation is obviously clueless as to wind-resistance and up/down hills, which will skew the results.

I don't have much else to go on, but I can say that on average I've been dropping almost as much weight as it says, so I believe it must be at least in the vicinity of accurate. On the other hand, your 2.5 hour ride apparently burned less than half as many calories and people are saying that your numbers are inflated.

Summary: colour me confused -- I never expected my computer to be terribly accurate, but based on my weight lost it certainly seems to be close to the mark; meanwhile your numbers are in a totally different ballpark from me.

I'll have to check out this "power meter" gizmo....
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Old 09-07-08, 08:15 PM
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Originally Posted by Smallguy View Post
I'm not really sure on the accuracy because muscle burns more calories than fat per pound so how does polar accurately calculate or is it not accurate at all?
ding ding ding!
If you can have a body fat analysis done, you could enter a more accurate weight into the Polar for the purposes of calories consumed.

It's not as easy as subtracting all of one's fat weight in pounds from overall body weight, because there is some metabolic contribution from adipose.
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Old 09-08-08, 02:55 AM
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Originally Posted by Caribou2001 View Post

Summary: colour me confused -- I never expected my computer to be terribly accurate, but based on my weight lost it certainly seems to be close to the mark; meanwhile your numbers are in a totally different ballpark from me.
Your weight loss will also come from other sources including calories burned off the bike and the calories that your body burns in recovery. So, your computer may say you burnt 3500 cals and you did lose a pound, but that doesn't necessarily mean your computer is accurate.

As to your numbers, your ~55 cals/KM is VERY optimistic regardless of environmental factors. Using a calculation I found elsewhere(cals burned/time x 1000 = watts) you would have had to put out an average of 366 watts for your 2.5 hr ride - an effort that would be at least pro level and perhaps beyond.
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Old 09-08-08, 05:05 PM
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ottsville,

Hey, that's a handy calculation!!! I have no doubt that I spun nowhere near 300+ watts.. I expect I varied between 60 and maybe 180 at the top-end (power to the pedals, that is). I wonder how accurate that formula which you found is... do you remember where it came from?

A few number I was able to find: 1 kcal = 4.184 joules; 1 joule = 1 watt; 100 watts = 86 kcal/hour...

So, I must be missing something, if you're saying [(kcal/time) * 1000 = watts] then 1000 kcal in 2.5 hours would be: [(1000/2.5) * 1000 = 400,000 watts] but if you meant to say [kcal/(time * 1000) = watts] then [1000/(2.5 * 1000) = 0.4 watts] and neither of those solutions looks like it has any basis in reality....

I understand that other activities also contribute to my weightloss, but I figured that if I went from eating 2500-3000 kcal/day and not losing weight, then went to eating 3000-3500 kcal a day and losing weight with my only variation in activity being the addition of cycling, then I must be burning a modest amount of energy while cycling. Beyond that lose qualitative analysis the rest of it is guessing for me

Of course, there's also the issue of efficiency -- to generate 100 watts on the pedal takes a top athlete 400-500 watts from their entire body, from what I can find... I am nowhere near a top athlete, so my efficiency is probably close to 15% or less, meaning I'd have to expend closer to 670 watts to get 100 watts onto the pedals....

All-in-all, a confusing topic for me! At least I'm losing weight and getting more fit, all while enjoying my time on the bike -- that's what counts in the end, I suppose, lol.

Thanks again for the info, however!
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Old 09-08-08, 06:50 PM
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I got that formula from HERE. My math is a little rusty but that seems to fit with the other stuff I've found.

So, I must be missing something, if you're saying [(kcal/time) * 1000 = watts] then 1000 kcal in 2.5 hours would be: [(1000/2.5) * 1000 = 400,000 watts]
You have to convert your time to seconds(1hr = 3600 secs) since watts relates to seconds.

SO:
1000Kcals in 2.5 hrs = 1000/(2.5 x 3600) x 1000 = 111 watts

At least I'm losing weight and getting more fit, all while enjoying my time on the bike -- that's what counts in the end, I suppose, lol.
Absolutely!
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Old 09-09-08, 06:37 AM
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Ahh, ok -- that's an important distinction! (Convert time to seconds). So, after looking at the link provided I see that 1 kilocalorie = 4.184 kilojoules, but they are simplifying and saying the relationship is 1:1 because of the inherent inefficiency of putting power to the pedal. A handy shortcut. So this formula is accounting for "waste" energy used to pump the heart, diaphram, stay balanced, etc...

So, I think I'm getting somewhere... Using dimensional analysis:

Given -> 4184 Joules = 1 kcal & 1 hour = 3600 seconds, then ->

4184 Joules / 1 kcal * 'n' kcal / 1 hour * 1 hour / 3600 seconds = Joules per second (or watts) therefore we can rearrange to solve for watts if given kcal, or solve for kcal if given watts:

watts = (4184 * 'n' kcal) / 'time in seconds'
kcal = ('time in seconds' * 'n' watts) / 4184

If we re-work the formula to assume a 24% efficiency, we can apply that to the kcal, i.e. (sticking with our 1000 kcal in 2.5 hours scenario to find watts...)

watts = [4184 * (1000 * 0.24)] / (3600 * 2.5) = 111.6 watts
______Joules^____kcal^__^efficiency_^sec_^hr.

Which agrees with the formula you found. I believe the 24% efficiency is for top athletes.... "Within a given population, muscular efficiency and thus work rate typically vary by as much as 2030% when comparing individuals with low vs. high efficiency" (http://www.pubmedcentral.nih.gov/art...?artid=1805800) but at the moment I can't find any ballpark estimate for a post-couch-potato 40-something efficiency at cycling...

At any rate, the final formulas are:

watts = (4184 * ['n' kcal * efficiency]) / 'time in seconds'
kcal = ('time in seconds' * 'n' watts) / (4184 * efficiency)

Where 'efficiency' is a percentage (on a calculator something like 0.24 = 24%).

Thanks again for the info! (Of course your formula works fine for calories to watts, but now we know how to go from watts to calories too.) That was fun, lol. Now all I need is a gross estimate of my efficiency when cycling.


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Old 09-09-08, 11:53 AM
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I always use these types of gadgets as an independent guide.
So the elliptical machine at my gym says 450cal burned. All I take away from that is that it gave me a score of 450 for the effort I put in. Now I can use that as a guide for whenever else I use that same machine. The same goes for everything else including other equipment, scales and body fat calculators. No consumer machine is going to calculate all the intricacies of your bodies metabolism.
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Old 09-09-08, 02:57 PM
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"So this formula is accounting for "waste" energy used to pump the heart, diaphram, stay balanced, etc..."

Most of this 'waste energy' is simply heat. - TF
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Old 09-10-08, 07:13 PM
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Mr.BoJingles and TurboTurtle -- thanks for the tips!
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Old 09-13-08, 07:51 PM
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I view the results from my Polar HRM as a relative measurement of the amount of energy burned, not an absolute number. It's "optimism" help me keep going at the beginning. There's something very satisfying about seeing those number of calories burned. Since I never acurately tracked intake I figured it was all an estimate anyway.

Interesting that I almost always average 70 kcal/mile, no matter what my effort level might be.
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Old 09-14-08, 11:50 AM
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I use the Polar F6 HRM to calculate calories burned. What I do though is subtract 1 calorie from the total calories burned for every 1 minute exercised. So I did 50 miles in 176 minutes and burned 1547 calories leaving me a total calores burned of 1371 calories.
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