Scepticism about HRMs - what's best for running?

meerkat70

I read through last night's discussion about speed and calorie burn, and it niggled again for me a concern I have around the accuracy of HRMs vs distance based calculations for running.

My garmin tracks my distance, speed and elevation, maps it against my weight, and gives me a particular calorie burn. This 'fits' with The American College of Sports Medicine estimates. My polar will give me a much lower estimate, for the same workout.

I'm never sure which one to take seriously. Based on my understanding of physics and biology, my guess is that actually, the garmin calculation is better, that it figures in more factors. But popular wisdom directs us to the accuracy of the HRM. One of my concerns about the HRM is that it doesn't factor in the law of diminishing returns that we *know* influences overall burn for a very long run.

To some degree I guess this is just academic, since it's unlikely I'll ever 'eat back' everything I expend on a run over 10 miles and more. But there's part of me just want's to know.... What are your thoughts?

IronSmasher

Volunteer to take part in a study where they need to accurately measure your burn Prof.

meerkat70

Volunteer to take part in a study where they need to accurately measure your burn Prof.

I'd love to do that. Unfortunately, I'm not aware of anyone actually *doing* such a study anywhere near to where I live. (*wanders off to look at the loughborough site, though... *)

Realistically, though, a lab context would only measure burn on a treadmill - I don't think that would transfer accurately onto the road?

bsharrah

I would say neither is any more accurate than the other. You can average the two for a ball park figure but that is as close to knowing as you will get.

Your skepticism is well founded. HRM's are not as accurate as many people think. It is fun to read threads about how people take the readings so seriously though. More entertaining than watching Tosh.0 sometimes.

dad106

I'd go with the Polar being more accurate of the two..Simply because it takes all your information, while the Garmin is only using weight.

Since the Garmin does not take into consideration age or gender, it could be assuming you are a male.. and thus giving you the calorie burn of one.

I use a GPS app on my phone that takes into consideration weight, age, gender and height, and it's pretty close to my Polar.

IronSmasher

Nobody is going invest a large amount to improve our current methods. Any time they need to accurately measure calories used, they're going to measure the oxygen used as it's easy and cheap enough for the rare occasions required.
Another thing against it is trying to argue the need for it, when so many other factors such as nutritional needs or supplies are not very accurate.

If you're going to argue about the differences between lab and road running, when they've gone to the trouble of isolating every physiologic factor, then you're just going to have to spend every road run with a mask and backpack on I'm afraid.

meerkat70

The garmin does take gender and weight into account.

My GPS phone app tends to overestimate distance, and gives a higher calorie reading than my garmin, which is more accurate for distance.

meerkat70

If you're going to argue about the differences between lab and road running, when they've gone to the trouble of isolating every physiologic factor, then you're just going to have to spend every road run with a mask and backpack on I'm afraid.

Will there be photos? :-D

IronSmasher

Maybe, unless you own enough property to get a decent run in?

meerkat70

I wish. Landed gentry, I'm not.

The gap between my hrm and my garmin isn't insignificant, btw. The polar estimates about 100cals per mile. Garmin gives me around 150. Add that up over 10 miles and it really is a big difference....

I guess my question boils down to heart rate as an estimate vs multiple physics based measures.

LorinaLynn

Unscientific, scientific approach... try eating all your exercise calories using one method for a few weeks, then try eating all your exercise calories using the other method for a few weeks. See which gives you better results.

IronSmasher

Unscientific, scientific approach... try eating all your exercise calories using one method for a few weeks, then try eating all your exercise calories using the other method for a few weeks. See which gives you better results.

So, what you're saying is, Meerkat should try one method for several weeks recording the results, try another method by changing one variable for several weeks and measuring the results, and then compare the two?

It's seems so simple... and so familiar. Where have I heard that sort of advice before?

drgndancer

The HRM does have access to one key piece of info that the GPS doesn't, how hard you are working. The same 10 minute mile pace is a completely different aerobic experience for an Olympic distance runner and a newbie. One isn't even getting their heart rate up, the other is giving everything they've got. The formulas that use distance exclusively assume that you're keeping your heart rate at a nice middle of the road aerobic level for the whole distance, that may or may not be accurate.

jstandfield

None of those things are accurate, there are too many variables not taken into account. Its best to use them as a base line to improve performance as opposed to how many calories you burn in a workout. The things to watch are improvement in pace and average heart rate during a run.

tappae

I would question the premise that an increased heart rate means an increased calorie burn. I think it often will, because they're strongly correlated. For instance, if I run the same speed up a hill that I did on the level, my heart rate would go up. I would also burn more calories, because of the increased work load of going up a hill. The calories and the heart rate aren't connected to each other, they're connected to the amount of work I'm doing.

Imagine two men who are the same height, weight, age, etc. and they both walk up the same flight of stairs. Let's say one of them is overweight and out of shape and the other one is fit and muscular. They're doing the same amount of work, right? They're moving the same mass the same distance. Now there may be some slight difference because of efficiency and the fit person could be said to be doing less work since some of their mass (leg muscles) is doing the moving more than being moved, but the calorie expenditure should be pretty close. If they're wearing heart rate monitors, presumably the sedentary individual would have a harder time and would get a higher reported calorie burn (especially if it takes them longer) and I don't see how that could be accurate.

tappae

To actually answer the question though, I think my HRM is pretty accurate for easy runs, when I'm keeping my heart rate in the aerobic zone. The database doesn't take elevation or terrain into account, and the elevated heart rate will add some calories for that. On the other hand, when I do intense workouts, the HRM gives crazy high numbers. I usually use the numbers estimated by runningahead.com. They're likely low for hill runs and trail runs, but since I'm only trying to eat back the first 700 anyway, I'm not too concerned about that.

timboom1

I wish. Landed gentry, I'm not.

The gap between my hrm and my garmin isn't insignificant, btw. The polar estimates about 100cals per mile. Garmin gives me around 150. Add that up over 10 miles and it really is a big difference....

I guess my question boils down to heart rate as an estimate vs multiple physics based measures.

Are you sure your Polar has all the right settings? 100cals/mile seems way to close to the baseline setting for 150lb person. 150cals/mile seems more realistic for where you are currently. That said, it may just be that you are getting more efficient and that is confusing your Polar.

Calories may be impacted efficiency, but it is not going to be that big a difference. In the end distance and weight are the two biggest factors in energy burn, with slight variations for everything else. A HRM can have a lot a variation, for running they are great for training so you know what % of Max you are at, but the calorie burn can be way off.

The calorie burn component of the HRM assumes a average amount of blood pumped per beat, this equates to the amount of O2 delivered to muscles which is what then allows then to burn fat or glycogen to produce energy (i.e. burn calories.) If you have been running awhile, the adaptations to the cardiovascular system, specifically, capillary and mitochondria propagation coupled with a stronger heart muscle, will allow a you to move more blood with each beat. This means, lower heart rate for the same amount of O2, supporting the same calorie burn. A HRM will not know about cardiovascular adaptations and tends to assume the lower HR means lower calories.

I tend to think of it like this, if my weight has stayed the same over the last year, but my resting HR has dropped from 60 to 48 over that same time, that basically means I need 20% less heart beats to maintain the same static "just staying alive" calorie burn, purely because I can move more blood with each beat.

...or my short answer, With your distances and experience, go with the Garmin over the HRM.

Azdak

I would question the premise that an increased heart rate means an increased calorie burn. I think it often will, because they're strongly correlated. For instance, if I run the same speed up a hill that I did on the level, my heart rate would go up. I would also burn more calories, because of the increased work load of going up a hill. The calories and the heart rate aren't connected to each other, they're connected to the amount of work I'm doing.

Imagine two men who are the same height, weight, age, etc. and they both walk up the same flight of stairs. Let's say one of them is overweight and out of shape and the other one is fit and muscular. They're doing the same amount of work, right? They're moving the same mass the same distance. Now there may be some slight difference because of efficiency and the fit person could be said to be doing less work since some of their mass (leg muscles) is doing the moving more than being moved, but the calorie expenditure should be pretty close. If they're wearing heart rate monitors, presumably the sedentary individual would have a harder time and would get a higher reported calorie burn (especially if it takes them longer) and I don't see how that could be accurate.

You are missing part of the equation. HRMs work on the principle that, during steady-state aeobic exercise, there is a predictable relationship between heart rate and oxygen uptake. In other words, "X%" of one's HR max is equal to "Y%" of one's VO2 max.

If you know that 85% of HRmax is equal to 70% of VO2 max and you know that the person's VO2 max is, say, 30, then when that person is working at 85% of HRmax, their VO2 is 21 (70% x 30) or 6 METs.

Since they don't actually measure VO2, HRM algorithms have to be more complex, but the principle behind them is still the same.

In the example you mention, if the HRMs were set up correctly, the calorie readings should be similar, despite the differences in fitness level. Yes, the unfit person's HR would be higher, and he would be working at a higher % of HRmax, but the VO2 max number would be significantly lower than the fit person.

If the less-fit person had a VO2max of 30, and the effort required 80% of VO2max, he would be working at a VO2 of 24.

If the fitter person had a VO2max of 40, the effort would only require him to work at 60% of VO2 max.

Since both men were working at a VO2 of 24, and both weighed the same, both would burn calores at roughly the same rate (as you suggested). Because of the difference in relative intensity, the less-fit person would have a higher heart rate. But, again, if he had his HRM set to the correct VO2max, the "scale" of HIS heart rate/VO2 relationship would take that into account, and the calorie number should be relatively accurate. The same with the fitter person--his HRM should be set at a different VO2max to take into account his higher fitness level. If both HRMs were set at the right "scale", then both should return similar numbers, since the energy cost of walking up stairs (the actual work being performed) is relatively fixed.

The problem with most people using their HRMs as "proof", is that few people have their HRMs set up correctly, or have HRMs that cannot easily account for differences in fitness level. If the HRMs are not set up correctly, the HRM interprets the higher HR as evidence of working at a higher ABSOLUTE intensity, and thus spits out an overstated calorie number.

It also leads to the erroneous conclusion that, as you become more fit, you burn fewer calories at the same workload. Unless you also lose weight, that is not true (not true to the extent that most people think--improved "efficiency" has only a very small effect--and that only happens after a very long period of time). You are not burning fewer calories--your HRM settings are just out of date.

tappae

It also leads to the erroneous conclusion that, as you become more fit, you burn fewer calories at the same workload. Unless you also lose weight, that is not true (not true to the extent that most people think--improved "efficiency" has only a very small effect--and that only happens after a very long period of time). You are not burning fewer calories--your HRM settings are just out of date.

Thanks for the info! This was the thought I was trying to respond to. I've heard this said a lot on MFP and it just doesn't make sense to me. It seemed that people were using their HRM results as some kind of scientific proof when they shouldn't have. It makes sense that the settings might just need to be changed, though.

I'm probably going to have to get a better HRM at some point. I like to keep most of my runs below a certain heart rate and I've had to learn how to do that by feel (after checking my rate at different effort levels for a few weeks) since I can't even rely on my HRM to accurately report my heart rate.

dbevisjr

Which model Garmin and which model Polar? Just because a unit gives heart rate info doesn't mean that it uses that info to calculate calorie burn. Many only use your age, gender, weight and elapsed workout time to calculate calorie burn.

meerkat70

It's a garmin forerunner 110, and a polar FT60.

Thinking about it, my polar tends to radically undercut the machines at gym (it tends to give a much lower reading), and the estimate it gives for my running is lower, it seems, than many of my lighter friends running at similar speeds. Leads me to suspect that I might have a dodgy hrm?

The HRM itself is definitely set up correctly, in terms of weight, age and gender.