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Old 07-19-12, 01:15 PM  
Pratima
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How accurate are HRMs?

I finally got a heart rate monitor strap for my Motoactv and tried it out this morning. I did the shorter cardio workout from the CLX set. According to my Motoactv data, I worked out for 24 minutes and burned 234 calories! I'm 5'1" and about 110 lbs right now. Doesn't that seem really high?

I use a Fitbit too, and just based on movement and the stats I've given it, it recorded 110 calories for the same time.

I don't really understand how HRMs calculate calorie burn. Would it be more accurate if I ran and the Motoactv also had GPS (distance) info?

So weird to think I burned that much in what I consider a sort of tough but not killer workout. How much did I burn with my 50-minute iTri the other day??
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Old 07-19-12, 01:23 PM  
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I consider them accurate with respect to measuring heart rate (assuming all contacts are working and battery is good). I consider all calorie burn algorithms used by a HRM to be an estimate. You can somewhat use it to compare one workout to another or one day to another (similar to monitoring a body fat% trend on a scale), but don't base your nutritional intake off of those numbers (in my opinion).
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Old 07-19-12, 02:09 PM  
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I think how accurate hrm's are for calorie burn really depends on the formula used. Thing is every device has it's own secret formula. My understanding is the more respected ones usually measure something like a 20% margin or error. I am not sure whether that means 10% high or low which isn't too bad, or 20% high or low, or whether it means they are accurate for 80% of the population. I think the margin of error only applies to steady state cardio though, not necessarily weight lifting.

Pratima, I am the same height as you, but heavier. Your hrm burn doesn't sound too crazy if it is an intense workout, but perhaps a little high for someone that is 110 pounds. I think your fitbit measure will be low if the workout was weight training. If it was cardio, perhaps. My fitbit and hrm actually agree on the calorie burn estimate for TurboJam for me, I am not sure what the CLX cardio is like. My hrm is a Polar F11 some comparing devices is a little like apples to oranges. I am curious which strap you bought though. I just ordered a bluetooth hrm strap with a gift certificate I had and am waiting for it to arrive. I think mine might also work with that device (though I don't have it) so that is why I am curious about your strap.

I do use my fitibt and hrm together as a basis for my nutrition calories, and it seems to work. But all calorie burn numbers from home devices (and maybe from labs) are estimates or even guesstimates as Sciencelady wisely pointed out.

My first hrm seemed to estimate burn soley from my profile specs (weight, age, gender) and *average heart rate* for the workout and duration. So if I tracked one dvd including warmup and cool down, my average would be lower and my total calorie burn for the longer duration would be lower. If another day, I tracked the same excluding warmup and cooldown, my average would be higher and my total burn for the shorter duration would be higher. Obviously, I didn't burn negative calories during the warmup and cooldown. So even though you can't know the exact formula it can help to notice the quirks of your device. My current hrm reports average hr, max hr measured during that workout, and time spent in each of three zones (the later Polar's seem to have five zones?). It seems to use the time in the three zones along with profile stats (height, weight, age, gender, estimated vo2max, estimated maximum heart rate, and resting heart rate) to estimate. So including the warmup and cooldown doesn't decrease the calorie burn for the same workout, though it does decrease the average heart rate. Sorry, too much detail but just showing how different devices will use different information and that will play into the estimate they give.
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Old 07-19-12, 02:12 PM  
Pratima
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That's reasonable. Here's what's really ridiculous. I used this target heart rate calculator, and based on the info I entered (just my age, 39) it says my target zone is 127-154. That's about what my max was today. I'm pretty sure it gets a LOT higher when I do intervals using a step, or when I run.

All this just makes me think that perceived exertion really is the best measure.
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Old 07-19-12, 02:45 PM  
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Is your target range ending with your maximum heart rate? I am guessing it is probably below it.

Maximum heart rate is quite personal and partially genetic from what I understand. I think mine is lower than the formulas give me as I rarely get out of the lower zone one, intense intervals where I am gasping for air tend to get me into upper zone 2 for a little while based on the standard formulas. The formulas (there are several different ones commonly used) are estimating based on averages of whatever population was in whatever studies. For an individual, it may be high or low. If you exceed your "maximum heart rate" during a workout, that isn't really your maximum as obviously you personally can go higher. There are some tests you can do to estimate your personal maximum heart rate, but to truly do it I think it should be under medical supervision. Maybe some of our endurance athletes can help with this.

One value to using a heart rate monitor is seeing how you adapt to a certain activity or all activity over time. You might find the exact same workout inspires a lower heart rate than before and a lower estimated calorie burn. This is a clue that if you want more benefit from it you need to modify up or move on or save it for recovery days, etc. The fitbit and gps won't give you that kind of changing over time feedback. Also, day to day, you might notice if your heart rate is higher or lower than usually for the same workout or activity. It can be influenced by weather, illness, coffee, whatever. I guess some people actually use this to see how well they are recovering from previous workouts too. I would like to know more about how to apply hrm information to recovery, but all I picked up is your resting and working heart rate is likely to be higher than average if not fully recovered from previous exertion. (Not sure if I understand or phrased that correctly).

Perceived exertion is a good guideline. I have to admit my perceived exertion seems to depend on whether I am bored or having fun so I don't fully trust it but I am more and more every day. Now I can usually guess my heart rate before I look at my watch now based on how I feel. But the numbers are generally lower all around than the formulas give for my stats. So what does that mean? LOL! I guess some of the value is comparing your own numbers with yourself, but early on you don't have a basis of comparison other than the numbers the formulas give.
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Old 07-19-12, 03:09 PM  
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Yes, I guess it is below. I didn't calculate max (yet). At 155, I didn't feel like I was working all that hard though, and I thought those CLX workouts are supposed to get you anaerobic. I'll definitely have to try some others and compare!

I guess the HRM can be for two pieces of info then--relative heart rate (comparing workouts, days, progress over time, etc.) and for relative calorie burn. I don't really base what I eat on calorie burn (from Fitbit or HRM data) but like most people, I do tend to eat more if I think I've worked really hard that day! I was a little surprised at the difference in calories between Fitbit and the HRM, but realistically 200-something isn't a lot. Like not enough to go stick my head in a tub of Ben and Jerry's or anything!
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Old 07-19-12, 03:48 PM  
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Originally Posted by Pratima View Post
That's reasonable. Here's what's really ridiculous. I used this target heart rate calculator, and based on the info I entered (just my age, 39) it says my target zone is 127-154. That's about what my max was today. I'm pretty sure it gets a LOT higher when I do intervals using a step, or when I run.

All this just makes me think that perceived exertion really is the best measure.
pratima,

the "field test" method is better, and your zones are sport-specific. for example, your zone for step aerobics would not necessarily be the same as biking.

i posted here on VF about when i used the age method and worked backwards, it said i was 63 YO, not that there's anything wrong w/being 63 YO. people with strong endurance will have lower thresholds.

also, someone with more endurance will require a lot more intensity to raise their HR.

for each type of sport, you can use your HRM to gauge "highest seen" and develop zones from that point.
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Old 07-19-12, 05:08 PM  
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pratima,

the "field test" method is better, and your zones are sport-specific. for example, your zone for step aerobics would not necessarily be the same as biking.

for each type of sport, you can use your HRM to gauge "highest seen" and develop zones from that point.
All this makes sense. By field test, do you mean recording my HR while doing various activities and using those as my targets?

And I would tend to think that if my zone for let's say biking is lower than for step, that maybe step is a more intense workout for me? Maybe that just means it's better for long, steady-state workouts rather than short, intense ones (which is what I'm going for now).

With limited time, I'm trying to figure out how to make the most of my workouts. I'm a little surprised at the data from the CLX cardio but really, I don't have anything to compare it to yet. I'll go to the gym Sunday and see how that compares.

On a semi-related note, the one day I managed to run outside (before it got way too hot) I went about 2.5 miles and was EXHAUSTED compared to the 2.5 miles I'd been doing indoors. My guess is that the impact wore me out. I wish I had HR info from that day too.
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Old 07-19-12, 06:22 PM  
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I'm sure you probably already did this, but did you enter your own weight into your HRM? Because otherwise, it's calculating based on a 150 pound male. That seems to be the default on them.... you should be able to enter that youare a 110 pound female somewhere and that might make a difference.
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Old 07-19-12, 06:44 PM  
Pratima
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Originally Posted by susan p View Post
I'm sure you probably already did this, but did you enter your own weight into your HRM? Because otherwise, it's calculating based on a 150 pound male. That seems to be the default on them.... you should be able to enter that youare a 110 pound female somewhere and that might make a difference.
Yes. When I set up the Motoactv, I put in all my stats. I keep thinking about this, can't decide whether 200-something calories seems realistic for that workout. I really do need some point of comparison.
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