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How accurate are heart rate monitors at calculating caloric expenditure?

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I use a heart rate monitor every time that I exercise.  Mostly this is so I can keep myself in a target heart rate range, but I also use it to determine my calorie expenditure.  Interestingly enough, when I compare my intensity, length, and type of workout with various exercise logs online (cc included), I find that my heart rate monitor says I've typically burned twice as many calories as these online resources.

 For example, if I road bike for 1 1/2 hrs (av. heart rate is only 135, or 70% of my max heart rate of 192), my monitor tells me I have burned a grand total of 1500 cal.  That is a rate of 1,00 calories an hour!  CC puts a similar workout at 520 calories/hr, which seems a lot more reasonable since my rides are done at a leisurely enough pace that I never feel winded and can maintain a constant pace for the whole duration. 

Obviously, online resources don't account for age, weight, and fitness level like my heart rate monitor can, but I am beginning to doubt the values that it is giving me, even if it is supposed to be 'more accurate'.


Edit: Just for clarifications sake, I have a new Timex Ironman Triathlon watch/heart rate monitor.

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1000 calories an hour on a bicycle is typical of an all out type effort.  A more moderate pace would be more in the 700 -800 range.  500 and hour would be at an easy pace. 

How did you determine your Max Heart Rate?  What info did you need to enter into your HRM?

My heart rate monitor asks for age, weight, and max heart rate.  My max heart rate was determined during interval testing (when I was racing my coach tested all our values).  Although that was about six years ago, I believe it to be pretty accurate. 

Other methods of calculating MHR based on age put me anywhere between 185-196.

Even though I am a little overweight (BMI 26), I am also still quite physically fit so I would suspect that I expend less energy during workouts than the typical individual.

Then it sounds like your HRM should have your zones right.  I think it's number sound high.

My HRM matches the tables on this sight pretty closely.

Hmmm, I've heard that each company uses their own algorithms to calculate caloric expenditure.  Perhaps a different HRM manufacturer would be more accurate.  What type do you use?

Somethings seems fishy about those numbers. as trh said, 1,000 calories on a bike requires a pretty good effort. I burn about 1,100 running at 7.5 mi/hr. When I bike at 150 bmp (max HR 200), I definitely do not burn that many.

I use an Oregon Scientific that I got about 10 years ago cheap.  Suunto and Polar seem to be the premier brands.  A lot of cyclists use Garmins and I'm told by some users that they over-estimate calories.

Does this HRM let you load your stats, age, weight, height sex?  does it have a strap for constant monitoring?

I've heard awhile back that the polar HRM tend to run high calorie counts for females- I don't know if that's true, but I go by my HRM for my workouts and think if it is off it's not more than 10 - 20%  

My hrm also has the fitness test to get the VO2max which will affect my cal burn too.


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I have a polar FT7 with chest strap and it seems as accurate as cc I love it

If your HRM thinks your weight is in kg, and you input your weight in lb, it will calculate your calorie burn as about twice what it should be.

Datum: I have a Polar s710i, and the calorie burn for running and biking match up very closely with CC's calculator (as well as different algorithms). And for me, 1000 kcal/hr is definitely not slacking (e.g. running 6 mph, biking 14-16 mph) (male, 40, 225 lb).

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