## Polar HRM Caloric Data

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Craigagogo
Posts: 380
Joined: Sun Jul 18, 2004 1:10 pm
How accurate do you think the data from Polar HRM is concerning calories burned? I've read in other postings that the power output (watts) can be off by as much as 5 to 10%. If there is an inaccuracy in power data then surely the caloric data would be off too. If it is off, how does it vary, positively or negatively (from the actual amount of calories burned)? Or is all this just unsubstantiated rumours?
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Juqi
Posts: 20
Joined: Sun Oct 31, 2004 11:42 am
It depends on the model you have. The S serie models are very accurate as the models below that aren't.

John979
Posts: 1045
Joined: Sat Jan 15, 2005 11:29 pm
First, Polar power meters are more accurate than you hear or read. Second, both are calculated independently. Polar uses an algorithm based upon various factors including age, weight, sex, heart rate, duration to estimate calories burned. Its accuracy is variable for many reasons, but it does provide a rough estimate of calories burned, but probably not accurate enough if you were strictly counting calories to lose weight.

One of the advantages of a power meter is that they measure kilojoules of energy expended, and kilojoules are easily converted to kilocalories. The only problem here is that human efficency varies from something like 21% to 26%, so even knowing your kilojoules of work there is going to be some inaccuracy regarding calories burned.

BTW, I just compared two power meter files, one a Polar, the other a Powertap. Same ride, exactly one year apart. Almost identical conditions, distance and average speed. The average power measured by the Polar and Powertap was the same, with only a 34 kj difference in work.

Looking even closer, I looked at the data from a small climb:

Polar
Duration: 5:20
Work: 109 kj
Distance: 1.387 mi

Min Max Avg
Power: 176 474 342 watts
HR: 145 177 171 bpm
Speed: 12.6 19.8 15.6 mph

Powertap
Duration: 5:38
Work: 110 kJ
Distance: 1.392 mi

Min Max Avg
Power: 122 431 325 watts
HR: 120 228 163 bpm
Speed: 9.1 21.3 14.9 mph

The higher power reported by the Polar is indicated b the faster speed on the climb. Soon I wll be doing simulanious comparisons.
Last edited by John979 on Tue Mar 15, 2005 10:20 pm, edited 1 time in total.
John979

Craigagogo
Posts: 380
Joined: Sun Jul 18, 2004 1:10 pm
I am using the A5 unit, is this one know for accuracy?
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jalapeno
Posts: 1340
Joined: Tue May 13, 2003 10:10 am
Location: Cornwall, UK
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I did read a scientific article based on proper lab tests and they reckoned the Polar calorific/power/VO2max calculations were within 8% for the vast majority of the population provided you had calibrated the HRM properly to your own parameters.

ras11
Posts: 859
Joined: Thu Sep 25, 2003 9:11 pm
Location: SC, USA
I used to use the 720 to approximate my caloric output. I found that it under estimating my output, as I based my caloric intake ( + basal rate) on it. I was dropping weight too quickly. I multiplied the Polar value by 1.1 or 1.2 to offset the error. I would urge you to be careful with this number... remember, it's just a number, and it doesn't really reflect what your body is doing or what it needs.

To be honest, I stoppoed paying attention to my diet some time ago. I found that a healthy-well-ballanced diet with lots of fruits and vegies (and not a lot of meat) keeps the weight off. Add in a multi vitamin with iron, and 15-20 hrs a week on the bike, and I gaurentee you'll be at optimal weight right quick. And you don't have to count calories or go deep into calorie debt (and feel like crap all the time). Trust me, when you eat well, you feel good. When you feel good, you ride faster!
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steevo
Posts: 47
Joined: Fri Nov 14, 2003 3:55 pm
that is like 1200 an hour? jesus
I rode 6 hours for 110 miles today and estimated 3000 burned. am i wrong?

John979
Posts: 1045
Joined: Sat Jan 15, 2005 11:29 pm
I did an 80 mile ride today of just over 4 hours that required 2945kj of work. This is net work. To get calories, use one of the following conversion factors:

25% efficient, kJ × 0.96 = kcal,
24% efficient, kJ × 1.00 = kcal,
23% efficient, kJ × 1.04 = kcal,
22% efficient, kJ × 1.09 = kcal,
21% efficient, kJ × 1.14 = kcal,

I would assume 23%, thus I burned 3063 calories on this ride, excluding BMR.

One of these days I will hook up the Polar and see what it calulates.
John979

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