Hrm accuracy

rayfromtx
rayfromtx Posts: 111
edited September 22 in Fitness and Exercise
This morning I rode the bike for 30 minutes with my new polar ft40. It calculated that I had burned 385 calories. MFP said 255. Which is right? The hrm said I averaged 77% of max hr for the 30 minutes. I don't want to kid myself.

Replies

  • robin52077
    robin52077 Posts: 4,383 Member
    My personal opinion:

    If your HRM was programmed with your age, height, weight, and sex, and has a chest strap, then I would go by the HRM. But I usually only eat back 3/4 of my exercise calories to factor in the "maybe it's too high" worry. Don't want to eat back too much if you didn't earn it.
    Also, I subtract 1 calorie per minute when I log it because I would have burned that even laying on the couch.

    So, based on your numbers, I would log 355 (385-30) and would eat back 1/2 to 3/4 of those.
  • MisdemeanorM
    MisdemeanorM Posts: 3,493 Member
    Go off your HRM not MFP. MFP is not set to your body size, age, weight, etc like your HRM is. But, you might always round down just to cover the margin of error and to account for cals you would have burned anyway had you not exercised.

    Edit: Ok, seems like Robin and I are on the same page! :laugh:
  • js97206
    js97206 Posts: 15
    I would ask how you got your max heart rate. Unless you did a max heart test on a treadmill or bike your max hr may be wrong. 220 minus your age, or any other such calculations are only estimates and can be 10 to 15 beats off. Also you said on the bike, was this an exercise bike or riding outside? If outside was it flat roads or hills? Riding outside has a higher rolling resistance so will burn more calories, which most calories burned calulators do not take into account. I do a little bike racing and have been for a number of years. So I have learned a lot about this stuff. Also remember unless tested in a lab, amount of calories in food and the amout of calories you burn are also just estimates. So while keeping track of these things will help with weight loss. It can also make you crazy if you hyper-focus on it. My cycling coach recommends doing an average of calories burned and consumed over three days, but averaging over the whole week would be best.

    If your max hr rate is correct you should go with you hr monitor. If it is an estimate you could drop 5%, and say you were at 72% of max hr and that would make it so you were not over estimating you max hr and calories burned.
  • rayfromtx
    rayfromtx Posts: 111
    I did a fitness test with the hrm. I guess that is to calculate the resting hr. I'm not sure if that is used in the algorithm for max hr. So far the max that it has shown is 89% which feels about right for the level of exertion I was putting forth. I ride outside and pump pretty hard and push harder if the rate starts to get near 75%. Yesterday was on fairly flat roads in Houston. Today was back home on hilly rocky dirt roads. It is definitely way harder at home. My hrm showed max 89% and average 82% for this morning's 25 minute ride. Calories burned 349. Does that sound even close to right for my 185 lb. 49 year old moderately fit for and American, body?
  • BoresEasily
    BoresEasily Posts: 582
    If you did a fit-test with the FT7 than I'd definitely go with your FT7 because MFP doesn't have any of that information. HRMs are accurate to about 85% or so I think the numbers were. If you want to cautious, only count 80%. If you were riding at an 82% average than yes 349 sounds very reasonable.
  • rayfromtx
    rayfromtx Posts: 111
    It's an ft40. I think that is similar to the ft7. Does it sync to their website and if so, how? Read all the instructions and it talks about doing it but doesn't say how. Thanks for the replies.
  • TrainingWithTonya
    TrainingWithTonya Posts: 1,741 Member
    Did you have any caffeine before your workouts? What about decongestants or asthma medication? If you've had any of those things, then your heart rate monitor would be reading an artificially elevated heart rate because of the effects of medications or caffeine, which could show you having a higher calorie burn then you actually had. That being said if you are on beta blockers for high blood pressure, the opposite is true. That's why I use a METs compendium like MFP because I can't get an accurate heart rate response to exercise because of my asthma medication and caffeine. However, I don't believe that MFP has all of the different categories for METs for cycling, so you may have picked a MET level lower then what you actually worked at because it wasn't available in MFP. Do you know what speed you were going? If so, I can look up the METs for you and figure the calories burned that way to see how that compares to MFP and your HRM.
  • Azdak
    Azdak Posts: 8,281 Member
    I did a fitness test with the hrm. I guess that is to calculate the resting hr. I'm not sure if that is used in the algorithm for max hr. So far the max that it has shown is 89% which feels about right for the level of exertion I was putting forth. I ride outside and pump pretty hard and push harder if the rate starts to get near 75%. Yesterday was on fairly flat roads in Houston. Today was back home on hilly rocky dirt roads. It is definitely way harder at home. My hrm showed max 89% and average 82% for this morning's 25 minute ride. Calories burned 349. Does that sound even close to right for my 185 lb. 49 year old moderately fit for and American, body?

    In your case, the biggest potential place for overcounting is if your actual HRmax is substantially higher than the age-predicted HRmax that Polar uses as part of the calorie calculations. The only way to determine that is to do a field test (which can still be inaccurate because many people cannot push themselves to 100% effort), or just observe. If you find yourself consistent maintaining exercise heart rates of 90%-100% of "max" for extended periods of time, then you might want to bump that HRmax number up a bit.

    Otherwise, road cycling is one the better exercises for using an HRM. Activity tables are often too inaccurate, because there are so many variables involved in road cycling--and they vary throughout the ride. The ACSM has no metabolic prediction equations for road cycling. The only other thing that I know of that might be more accurate would be a power tap that would accurately measure watts. That's what the pro riders use. However, that's a lot of trouble and expense and not worth it for a recreational rider. Even if the HRM is off 15%, that's still only 50-75 calories--virtually meaningless in the big scheme of things.
  • rayfromtx
    rayfromtx Posts: 111
    Thank you so much for the replies. Tonya, my cateye is broken but doing the math, I was just over 10 mph, but on the rough hilly roads I ride, the charts won't do much good will they? The roads are very rough and compared to pavement, well there is no real comparison. I will use the hrm for now and not eat back more than about half the calories. I'll watch closely to see how that works out.
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