How true are MFP's Exercise Calories Burned?

I assume they over estimate a lot but some things are pretty accurate. The biggest problem if a 6'4'' 325lbs man runs 6mph for 30 minutes he is going to burn a lot more calories than a 5' 4'' 130lbs girl.

For running at least you can use an app. I run 3 gps apps on my phone (Nike+, Endomondo and iSmoothRun which syncs to RunKeeper). End result is that I get 4 (RunKeeper takes the app data and uses its own calorie algorithm on it) which take into account my pace, weight and even the cadence of my stride.

I always use the lowest # of calories, but usually all the apps are close. And nowhere near MFP.

using my HRM and in comparison, I have found MFP's numbers some are high and some are lower than my HRM. So needless to say I dont exactly trust them but for a general guideline for those without a HRM, guesstimate a little lower than MFPs numbers

I assume they over estimate a lot but some things are pretty accurate. The biggest problem if a 6'4'' 325lbs man runs 6mph for 30 minutes he is going to burn a lot more calories than a 5' 4'' 130lbs girl.

It does take weight into consideration - my exercise calories burned go down as I lose weight (based on the same exercise).

I just got an HRM - but am finding the numbers to be pretty close - withing 5% most of the time. Perhaps it overadjusts for the weight difference and is closer now that I'm getting closer to a healthy BMI?

I have read that heart rate monitors really aren't that accurate at estimating calories burned. Even this article that states Polar heart rate monitors are pretty good say they are only about 75% accurate (http://www.livestrong.com/article/490909-the-accuracy-of-calories-burned-in-polar-heart-rate-monitors/). I have no idea if their numbers are right, but I have seen many places saying heart rate is not a good predictor of calories burned. Even devices such as the Bodymedia Fit and BoduBugg don't even use heart rate at all because they say it doesn't add value to their methods. I wear a heart rate monitor and like it, but I'm not sure the calories are accurate. My Garmin 305 was usually within 10% or so of my Bodymedia Fit, but I think it uses distance ran, weight, and gate to estimate calories.

Also, heart rate monitors typically only do a decent job with activities like walking and running, not strength training: http://www.sparkpeople.com/community/ask_the_experts.asp?q=75

it's definitely over the actual amount. Compared to the HRM its at minimum 100 or more calories higher

I have read that heart rate monitors really aren't that accurate at estimating calories burned. Even this article that states Polar heart rate monitors are pretty good say they are only about 75% accurate (http://www.livestrong.com/article/490909-the-accuracy-of-calories-burned-in-polar-heart-rate-monitors/). I have no idea if their numbers are right, but I have seen many places saying heart rate is not a good predictor of calories burned. Even devices such as the Bodymedia Fit and BoduBugg don't even use heart rate at all because they say it doesn't add value to their methods. I wear a heart rate monitor and like it, but I'm not sure the calories are accurate. My Garmin 305 was usually within 10% or so of my Bodymedia Fit, but I think it uses distance ran, weight, and gate to estimate calories.

Also, heart rate monitors typically only do a decent job with activities like walking and running, not strength training: http://www.sparkpeople.com/community/ask_the_experts.asp?q=75

Depends on which Polar, and are you accepting default values, or figuring out your own stats, and sadly, are you male or female.

3 guesses as to which gender get's defaults that are most inaccurate. First 2 don't count.

http://www.myfitnesspal.com/topics/show/459580-polar-hrm-calorie-burn-estimate-accuracy-study

Correct on aspect that anything non-aerobic, actually, steady state aerobic, will be inaccurate. So wearing it all day, or for intervals, or weight lifting, those are either anaerobic, or not steady state, or not aerobic between 90-160 bpm.

Edit: very true on the Garmin 305 - didn't even use HR is calorie estimates. But the newer Garmins use a algorithm from Firstbeat that studies have shown to be very good, and actually for anaerobic too. Because it incorporates your VO2 and breathing rate.
It's very interesting that later in a ride, even with the HR the same, the calorie count will go down because I'm breathing easier. It can tell the HR is elevated from heat, not effort to produce energy. Very cool.

Interesting......my Polar FT7 is giving much LOWER calories burned than MFP says...........I am big (6'4") and heavy (104KG) but not massively overweight, only a little and I play a lot of squash which is high heart rate stuff..........but on my walks/runs, I'm getting a much lower (typically 50%) reading of calories burned off the HR monitor than MFP's estimate.............thoughts anyone?

The exercise database that MFP uses only takes into account your weight, not gender, not age, and of course no idea of your level of effort.

I just did an hour recovery walk last night, and actually MFP was only 20 cal higher that HRM.
So their entry for walking 4mph (which they don't know hills too, right, 4mph up hills is harder than flat) must be based on about a HR of 40% of max - which is not much effort at all.

So if walking 4mph is harder effort for you and your HR reaches 50-60%, than MFP will underestimate.
If it is even less effort because you did keep it flat perhaps, than MFP will overestimate.

If you are heavy but got the muscle to make it not that difficult, likely MFP will overestimate.

Here is calculator that is interesting if using treadmill - because the energy to move certain mass a speed and distance at an incline is mathematical, and interesting comparison as to how efficient your system is.

http://www.exrx.net/Calculators/WalkRunMETs.html

i think MFP also needs a spot where you can put your known bofy fat % so it can more accuratlly calculate your calories and true bmi

My HRM has been pretty closes to MFP. I don't work out with the same intensity each time so it fluctuates. Sometimes lower then MFP, sometimes higher and sometimes nearly spot on.

They are low for me so I calculate my own calories burned by heart rate

They're low for me too. I'm 5'9", 174lbs and my calories burned, according to my heart rate monitor, is always higher. If you're interested in an HRM check out the Polar brand. They have a whole range of monitors to fit your needs. There are also basic HRMs at Walmart and Target.