Author Topic: HRM and calories  (Read 3868 times)

HRM and calories
« on: April 24, 2008, 09:06:04 am »
I know the calorie calculation by HRMs is a very rough and ready measure, but...

Today for various reasons I needed to drive to work. As I'm also doing some experimentation with my Edge 705 (around what happens as the dynamic memory fills up), I've got the HRM strap on.

Driving in to work took 28 minutes 42, average HR 56, max 66. You can guess from this that I don't drive in a big city  :) Calories burnt 716, equivalent to 1497 per hour.

Cycling in yesterday by a route that is a couple of Km longer took 37 minutes 20, average HR 160, max 185 (my actual max is around 205, so I hadn't pushed too hard yesterday). Calories burnt 720, euivalent to 1157 per hour.

So, apparently, sitting in my car with an almost resting heart rate burns more calories per hour than riding my bike! No wonder I find myself chomping on sweets as bonk rations on long drives :-)

Re: HRM and calories
« Reply #1 on: April 24, 2008, 09:16:29 am »
This is why I ignore HRM/cycle-computer kcal counts. They're simply meaningless.

I think you're seeing this because the Edge series uses the current speed in its kcal calculations. So, for one 10 second period it would simply stick "50mph, 60bpm" into its kcal equation and out pops a number. It tots up these numbers and gives you the 716kcal burnt for driving in result.

My cycle-computer thinks that the slower I'm going, the fewer kcal I'm using. And the faster I'm going the more I'm using. Of course I'm usually going slowly uphill and working hard, but burning fewer calories than I am taking it easy going faster on the downhills.
"Yes please" said Squirrel "biscuits are our favourite things."

Re: HRM and calories
« Reply #2 on: April 24, 2008, 09:44:52 am »
Even when I use my HRM on my bike, I get a figure that's probably twice what I would expect.

Most of the time, I suspect I burn 300 - 400kcals an hour when cycling around here, or on a flattish audax.

Re: HRM and calories
« Reply #3 on: April 24, 2008, 10:04:33 am »
Even when I use my HRM on my bike, I get a figure that's probably twice what I would expect.

Most of the time, I suspect I burn 300 - 400kcals an hour when cycling around here, or on a flattish audax.

Based on lots of dull analysis of food intake, weight loss, HRM and cycle-computer figures, various web-pages, GPS tracklogs and elevation data, http://www.kreuzotter.de/english/espeed.htm and lots of handwaving, figures plucked from thin air and guesswork. I'd agree with that.

From what I can work out, my cycle computer (Cateye Velo 8) gives vaguely accurate figures (probably within 10% of the real consumption).

For my commute in (which I go at pretty hard and average about 28kph) it's about 500kcal/hour.

For an Audax (20-24 kph) it's 300-400 kcal/hour.

My Polar HRM gives kcal consumption figures pretty much almost double these, and therefore wrong.

But for running, the HRM kcal figure is reasonably accurate, but a little high, in that it fits with expected kcal consumption figures based on the treadmill speed and my weight.

I can maintain 160bpm on the bike for hours on end (indeed I averaged 160bpm for the first 200km Audax I did). But I can't maintain 160bpm whilst running for anywhere near as long.
"Yes please" said Squirrel "biscuits are our favourite things."

hellymedic

  • Just do it!
Re: HRM and calories
« Reply #4 on: April 24, 2008, 10:05:39 am »
Maybe you misread the HRM.
Driving around with a low heart rate will consume around 100kcal/hour.
Consuming 72Cal for your commute or 150 per hour sounds reasonable.
There's either a decimal point error or the algorithm is pants!

Re: HRM and calories
« Reply #5 on: April 24, 2008, 11:16:24 am »
Maybe you misread the HRM.
Driving around with a low heart rate will consume around 100kcal/hour.
Consuming 72Cal for your commute or 150 per hour sounds reasonable.
There's either a decimal point error or the algorithm is pants!

and/or there are electro-magnetic waves from the car affecting the HRM - this seems to be a common problem in gyms, where rotating flywheels in static bikes send out waves that  disrupt HRMs
"What a long, strange trip it's been", Truckin'

hellymedic

  • Just do it!
Re: HRM and calories
« Reply #6 on: April 24, 2008, 11:23:36 am »
Do mobile phones or Bluetooth gadgets interfere with HRMs then?

border-rider

Re: HRM and calories
« Reply #7 on: April 24, 2008, 11:25:10 am »
Do mobile phones or Bluetooth gadgets interfere with HRMs then?

Bluetooth no.  Mobile phones can if they're close, but it's the low frequency magnetic fields from the battery that causes the problem, not the mobile phone signal (usually)

HRMs use an audiofrequency magnetic field to communicate twixt chestband and readout, and anything that can swamp that can cause issues.  Shop antitheft systems, power lines and car environments all can.

Mrs MV's old car (Alfa) had an electromechanical gearshift system, with paddles on the steering wheel, and if I had the HRM on it used to go to 270 BPM every time I changed gear.  In my current car (Mercedes) it just sullenly reads zero while the engine is on.

tiermat

  • According to Jane, I'm a Unisex SpaceAdmin
Re: HRM and calories
« Reply #8 on: April 24, 2008, 11:31:52 am »
Apparently new (i.e <18 months old) BMWs cause problems with HRMs.  Dunno why, must just be something weird about them (apart from the obvious).

The place I used to ride around mid last year used to play havoc with my HRM, probably due to proliferation of Beemers AND power pylons.  I used to return from a ride to find my average HR was 260bpm, with a max of >300!!!!!
I feel like Captain Kirk, on a brand new planet every day, a little like King Kong on top of the Empire State

hellymedic

  • Just do it!
Re: HRM and calories
« Reply #9 on: April 24, 2008, 11:33:36 am »
Thanks. The OP's heart rate apparently never exceeded 66, which suggests there may not have been interference to me.

My quartz analogue wristwatch used to interfere with my HRM, adding 60 only when the wristwatch was almost on top of the HRM display.

Re: HRM and calories
« Reply #10 on: April 24, 2008, 11:37:06 am »
Maybe you misread the HRM.

Nope, it's not easy to misread, but clearly is giving a ludicrous figure.

Quote
Driving around with a low heart rate will consume around 100kcal/hour.
Consuming 72Cal for your commute or 150 per hour sounds reasonable.
There's either a decimal point error or the algorithm is pants!

It seems to have been taking speed into account; since arriving at work I've burnt no calories  - so this ties in with no apparent interference from the car (a nice steady reading whenever I glanced at it, and no spurious maximum being recorded).

Actually, the algorithm does have the possibility of being quite sophisticated; the box knows how much I weigh, how much the bike weighs, the speed I'm travelling, my cadence, altitude and my heart rate. The only things it doesn't really know are what the inefficiencies in the system are (how poor my transmission or tyres are, how rubbish the road/track surface is - e.g. plugging through mud compared to smooth tarmac, how poorly my body works internally), and if it is me or an internal combustion engine pushing all that weight up the hills.

border-rider

Re: HRM and calories
« Reply #11 on: April 24, 2008, 11:38:40 am »
Thanks. The OP's heart rate apparently never exceeded 66, which suggests there may not have been interference to me.

I was going to say the same, but it is possible that there was interference and that the displayed value wasn;t the same as the one that was being used in the calculation, or there is another sensor or amplifier  (like cadence or speed) that is being swamped and causing weird software effetcs.  I've seen that happen just occasionally in high magnetic fields - an ionising radiation monitor which showed background levels but kepot setting off its dose rate alarm, for example

edit: or it was just using the car's speed ^^ :)

Quote
My quartz analogue wristwatch used to interfere with my HRM, adding 60 only when the wristwatch was almost on top of the HRM display.

Analogue watches are quite good magnetic field meters.  My old one used to spin if I went to the bad bits of power stations.

Re: HRM and calories
« Reply #12 on: April 24, 2008, 11:57:48 am »
Actually, the algorithm does have the possibility of being quite sophisticated; the box knows how much I weigh, how much the bike weighs, the speed I'm travelling, my cadence, altitude and my heart rate. The only things it doesn't really know are what the inefficiencies in the system are (how poor my transmission or tyres are, how rubbish the road/track surface is - e.g. plugging through mud compared to smooth tarmac, how poorly my body works internally), and if it is me or an internal combustion engine pushing all that weight up the hills.

It may know how much you and your bike weighs, and a whole load of other stuff, but it doesn't take into account the single biggest factor that affects the amount of effort you have to put in.

Wind resistence, which changes based on the wind velocity.

Using the default figures at: http://www.kreuzotter.de/english/espeed.htm and selecting "hands on the tops":-

With a 10mph tailwind you can cruise along at 23.8mph by only putting in 160W. That's 550kcal an hour.
With a 10mph headwind you may up your power input to 200W to so that you're doing 13.3mph. That's 688kcal an hour.

And with a 10mph headwind, to get to 23.8mph you'd need to put in close to 700W. That's 2407kcal. (Obviously you'd adopt a more aerodynamic position, but even with tri-bars you still need to put in 420W to get to that speed, and that's still 1444kcal an hour).

So without knowing the weather conditions, or power input (the Edge 705 can get data from some Power measuring devices), the figures can be wildly inaccurate.
"Yes please" said Squirrel "biscuits are our favourite things."

Re: HRM and calories
« Reply #13 on: April 24, 2008, 12:38:13 pm »
So without knowing the weather conditions, or power input (the Edge 705 can get data from some Power measuring devices), the figures can be wildly inaccurate.

I know that, it just amused me this morning to see such a graphic demonstration :-)

I'd be interested to try out a power meter, but not enough to spend the equivalent of another decent bike on it. Collecting data appeals to the engineer in me, though I'll readily admit that it isn't likely to make much difference to my performance :-(

Regulator

  • That's Councillor Regulator to you...
Re: HRM and calories
« Reply #14 on: April 24, 2008, 03:09:23 pm »
I've got quite a good sheet for working out calorie use at home.  If I remember, I'll stick the formula up later.  It was one I got from one of the sport scientists at Loughborough, which they use.
Quote from: clarion
I completely agree with Reg.

Green Party Councillor

Re: HRM and calories
« Reply #15 on: April 24, 2008, 03:17:22 pm »
I'd be interested to try out a power meter, but not enough to spend the equivalent of another decent bike on it. Collecting data appeals to the engineer in me, though I'll readily admit that it isn't likely to make much difference to my performance :-(

Same here (especially the data collection part, I am a dreadful statto) and after much searching/browsing/reading I've come to the conclusion that a bike mounted power meter is just a bit too much for my needs. I'm no racer, I don't even do TTs (but I'd like to have a go in the future). I don't like getting close to the vomit threshold. Give me a 300km Audax any day.

A simple HRM provides all you need to do the vast majority of training.

I am interested in the Garmin Edge GPS + HRM logging (which is why I'll be interested in the results of your dynamic memory experiment as it's one of the deciding factors of 305 vs 705) but that's more of a toy than a useful tool.

For analysing my performance, and targeted/specific training then I'm going to get a Tacx iMagic and do a small bit of turbo work. I can use the turbo for some interval training (much easier than trying to do it on the road) and also use the set rides for performance analysis.
"Yes please" said Squirrel "biscuits are our favourite things."