HUGE calorie calculation difference Whats up?

I know when I used my polar HRM doing weights I would burn more then a 30 min run on the treadmill I would work out for 75 mins each day half running half weight training and I would burn 1000 cals so I would go with the Garmin and knock off a 100 or 200 cals for good measure : )

I am still wondering about calorie counts, almost to the point of giving up. I use a Garmin 910XT Heart Rate monitor, along with the deluxe strap, and a footpod for my exercises indoors. Today, I worked out with weights for an hour and 44 minutes, doing my arms and legs routine, along with a 10 minute Rowing machine warm up. The 910XT states that this activity burned 1331 calories. This total gives me a negative calories consumed for the day.

However, I have also been using Firstbeat Athlete, and am wondering, the same data, using the same .FIT file, (the file that the 910XT exports), Firstbeat states I burned 483 calories. This is a HUGE difference, and I cannot figure out which is "closer" to my actual calorie burn.

On the other hand, I also use the 910XT along with an iBike power meter when I can go on a bike ride. Yesterday, I did some calibration runs, totalling approximately 12 miles, in about an hour and a half, and the 910 gave a calorie count of 405. This seems fairly close, as the average speed was only 8 MPH, but there was a bit of a wind factor. The same data in Firstbeat states that I burned 562 calories! These numbers seem pretty close, and I would tend to lean toward the Garmin count on this one, but the huge difference for "regular" weight training seems way off. Anyone have any ideas why the discrepancy?
Any help/info is greatly appreciated.
Steve

HRMs are generally terrible for measuring calories. Heart rate only loosely corresponds to oxygen consumption (calorie expenditure is directly related to oxygen consumption. It's also different for every person.

Your heart rate increases in response to oxygen demand by your tissues. The theory is that, if you know how fast your heart is beating, you know how much oxygen is being demanded and therefore used. The problem is that you have no idea how much oxygen your system can deliver per beat. It's wildly different for every person. Indeed, as you become more trained the amount of oxygen delivered per beat goes down significantly. HRMs make random guesses in the dark about your VO2max (the measurement of oxygen delivery).

On top of that, heart rate is affected by many other variables. If someone scares you and your heart starts racing, you're not suddenly burning tons of calories. But your HRM would think you are. Some caffeine will make your heart rate increase - but your energy consumption won't go up much. And weight training is the worst. Lifting just doesn't consume many calories, but it makes your heart pound like you're sprinting.

I'll tell you straight up you didn't burn 1331 calories in less than an hour of lifting and rowing. That's ridiculous in the extreme. Your HRM is straight-up feeding you BS.

In my opinion, devices that track actual movement like the Fitbit or Bodymedia Fit are much, much more accurate than HRMs. HRMs are just awful for calorie expenditure.

First, I want to thank all for the input, and I think I'm going to continue using the calorie count from Firstbeat Athlete, it seems more realistic, at least for the weight training, days. The days when I can ride my bike, I'll use the joules calculation from the iBike power meter, and I honestly believe that one is probably the most accurate for that type of activity. I was thrown a bit as the documentation for the Garmin says that the "Calorie expenditure, and heart rate analysis provided and supported by Firstbeat Technologies, LTD". I would suppose they don't do the complete analysis the same as what Firstbeat says in their white papers on how they calculate Training Effect, and "energy expenditure". Okay, well, I think that's the plan, I do appreciate the input from everyone! Always good to have a 2nd, 3rd, or 4th opinion.. :-)

Estimating calories during resistance training is always problematic because the HR-VO2 relationship that exists when doing cardio does not hold when doing resistance training. I know that First Beat claims that their software can show EPOC and accounts for cardiovascular drift, but the R-R analysis that is the core of the First Beat analysis engine is still based on the physiologic dynamics of cardio exercise, not resistance training.

There are issues between the more advanced analysis of the First Beat software and the "native" software used for the numbers on the display. I have looked at some of the discussions, but, not owning any of the devices or software, I can't provide any detailed advice.

If you have gone to the level of purchasing a 910 and the First Beat Athlete software, then I am assuming you are interested enough (obsessed enough? :happy: ) to have looked into some of these issues, but here is an example of a discussion on one of the Garmin forums:

https://forums.garmin.com/archive/index.php/t-25085.html

It may be just something as simple as the more detailed the analysis, the more variability is revealed that is inherent in our physiology.

Reading through some of this stuff has started to pique my interest again in one of these more advanced devices, even with all of the extra work involved. For data geeks, it is like porn.

Remember: just because it's data doesn't mean it's good data.