Garmin 705 Calorie Counter

ob

Hi all

Does anyone know how the Garmin 705 calculates how many Calories you've burnt? I'd like to think it's some clever formula based on heart rate/cadence/speed/weight and that it's accurate, but I'm thinking it might be slightly off for me.

I've just been for a 57:00 ride where I supposedly burnt 1316 Calories. Please bear with me through the maths... I read somewhere that for every 1 KJ of energy put through the pedals, the body burns about 1 Calorie due to inefficiencies within the body, etc. This would mean that I put 1316KJ of energy through the pedals, or 1316000J.

=> 1316000J in 57 minutes

=> 23000J per minute, on average

=> 383J per second, on average

=> 383 Watts, on average

383 Watts is quite high.

This tells me one of 3 things:
a) I didn't burn anywhere near 1316 Calories, or
b) I did burn 1316 Calories, but the "1 Calorie per KJ through the pedals" assumption is wrong - either in general or for me personally, or
c) Everything was correct and I did average 383 Watts and I'm therefore amazing :P (not likely!)

Any thoughts anyone?

nferrar

The Garmins are well known for having a shite calorie calcuator, I think everyone jsut ignores it.

Bronzie

This is what you'd look like if you ate the calories the Garmin just told you you'd burnt:



The one on the left BTW

athers08

I went on a ride today with my Edge 705, here are the stats:

Time: 4hr 15min (moving)

Distance: 103km

Calories: 4065

avg Heart Rate: 149

I'm 80kg

I've only had the garmin unit a couple of weeks, and was starting to think that the calories total was a bit high, compared to my previous polar unit.

I use a fortius tacx turbo trainer with a polar hrm strap, and my last ride had these stats:-

Time: 1hr43min

Distance:- 53km

Avg Heart Rate: 139

Calories: 887

Garmin was 850 kcal per hour and tacx was 506 kcal per hour - obviously was trying a bit harder out on the road today, but thats a big difference.

Any thoughts?

a_n_t

nferrar wrote:

I think everyone jsut ignores it.

halfing it was the outcome on motionbased!

DaSy

Yeah my 705 is insane when it comes to calories. My Polar generally puts me around 800 cals an hour when I'm pushing fairly hard, as opposed to the 705 that gives me about 1300 cals.

I now just assume 800 x hours of ride to give a rough guide.

franklinmall

Hi everybody, first time poster here. I’ve been using a sort of mapping system by Telenav. It is really useful to me because I can see other people’s bike routes and the best part is calculating the calories I can burn. (see it here: http://maps.telenav.com/tnmap/). Just wondering if anybody has a calorie counter they recommend?

sampras38

a_n_t wrote:

nferrar wrote:

I think everyone jsut ignores it.

halfing it was the outcome on motionbased!

Yeah, that's pretty much how I read my 705. I guess you can try and work it out roughly per hour, but it'll still be miles off. You could burn anything from 600-900 per hour.

ride_whenever

there is not really an effective calorie counter, waaaaaaaaaaaaaaaaaay too many variables.

The only way would be to look at your CO2 output i think, then back calculate the amount of respiration that would correspond to, you'd possibly need lactate levels and body temperature as well.

Alex_Simmons/RST

ride_whenever wrote:

there is not really an effective calorie counter, waaaaaaaaaaaaaaaaaay too many variables.

The only way would be to look at your CO2 output i think, then back calculate the amount of respiration that would correspond to, you'd possibly need lactate levels and body temperature as well.

while that's true, if you have a reasonable understanding of your own cycling efficiency from performing an appropriate lab test (ranges typically from ~ 19-24%), then a power meter will provide the most accurate information on calorie usage. Cycling efficiency doesn't change much over the long term, making PM data highly reliable.

Gav2000

Try multiplying your weight in the Garmin by a factor of 0.6; an 80kg rider should therefore enter their weight in the Garmin as 48Kg. This reduces the number of calories it says you have burned to a more reasonable level.

Gav.

robbiedont

As far as I've been told, there is a way to calculate fairly accurately calorie consumption BUT its patented by Polar or Sunnto and they don't let anyone else use it!

hopper1

A certain young lady posted the other day, that although her 705 is set at 60% of her weight, her unit still recorded almost 66,000 cals on a recent ride!

I never even look at the Garmin calorie counter...

ut_och_cykla

I've also heard Garmin thingys dont give very believable calorie counts.

I have a Suunto HRM and hubby has another make - when we ride together we get similar figures (we are of similar weight) and these tie in well with various speed/watts/calorie counters on the web.

For an item that isnt exactly cheap I'm a bit gobsmacked that garmin (and other HRM manufacturers) havn't either fixed this issue or at least included a disclaimer in thier manual!

I can imagine there are people who have bought the whole bike/hRM/clothes kit (yes people do here in Sweden anyway - just walk into a bike shop and say kit me out as a fast cyclist!!) and who are training to get fitter and slimmer and scratching thier heads because the expensive bit of kit says thy're burning1500 kcal and they're eating accordingly when really they're only burning 700. oops!

amaferanga

But the algorithm used by Garmin seems to varies from device to device. My Garmin 310xt underestimates on calories.

Some algorithms may be better than others, but no way can you accurately determine calories burned from just speed, HR, elevation, etc.

ut_och_cykla

I agree - accuracy must be debatable when all its based on is weight, age, max pulse but nevertheless physics says that moving a body over a certain distance at a certain pace uses a given amount of energy - and that can be calculated and as ob points out with fairly simply maths
Garmin grossly overestimates - even though it also gets info about speed (and altitude?) . my opinion is that Suunto calculates pretty reliably for me when I look at times, terrain and weather conditions as well and yes a Power meter woudl do an even better job but How Gramin can sell a product that is so wrong is beyond me :?

Jeff Jones

I've been using a 705 in conjunction with a power meter and even with this data available it still gets the calories wrong.

e.g. this ride (http://connect.garmin.com/activity/34960400) burned about 220 (avgW) * 3600 (sec) * 5.1 (hrs) / 1000 = 4039 kJ = about the same in Calories, once the conversion and efficiency factors are cancelled.

Garmin's own calculator said I burned 6691 Calories.

It's so far out that it's not worth using. Although multiplying by 0.6 gets me 4014 Cal - not bad.

Heckler1974

Isn't there something about Garmin not being willing to licence the algorithm for accurate calorie count so it makes an educated guess that equates out to constant climbing?

alien

OK - the Garmin 705 calorie count is borked - we know this. Roughly 1/3 more than my Suunto setup which uses the 'firstbeat' analysis system.

Garmin *have* licensed this, but I spoke with the Garmin Edge product manager late last year and there are no plans to get this into the 705 or any software that they currently have available.

You're looking at the 'next gen' for this to be in their kit and your guess is as good as mine as to when the '805' will be announced/out that *may* have firstbeat inside.

Till then, swop systems if the calorie side is vital to you, or get your data into something that has a better analysis system.

sorry.

magliaceleste

Garmin don't actually need to licence anything. Lets face it if they just used their existing (rather poor) algorithm and then simply subtract 40% from the calories "used" then Bingo they would have something a damn sight closer than they have now.

Without a power meter it's all a bit of guesswork anyway. What is even worse is that even when you have a Powermeter, the Garmin still can't get it right. That's pathetic.

amaferanga

magliaceleste wrote:

Garmin don't actually need to licence anything. Lets face it if they just used their existing (rather poor) algorithm and then simply subtract 40% from the calories "used" then Bingo they would have something a damn sight closer than they have now.

Without a power meter it's all a bit of guesswork anyway. What is even worse is that even when you have a Powermeter, the Garmin still can't get it right. That's pathetic.

Like I said above, not all Garmins are equal. They seem to have different algorithms for different devices.

magliaceleste

I was referring to the 705 mentioned in the OP.

The point about power still stands regardless, AFAIK even the 500 still doesn't use power output (if available) to calculate cals.

andrewjoseph

My understanding is that the 705 (and others) does not use HR in conjunction with distance. time and weight.

I use Ascent (Mac software) to log all my 705 data onto, this calculates using HR and everything else. Gives me around 900-1000 Kcal/hour burnt.

This corresponds to the info from my cyclosport HR monitor.

The 705 and garmin software give 1000-1200 Kcal/hour.

When on my own I tend to ride at 80-90% of max HR for most of the ride.

Finbar Saunders

When I import my 705 data into SportTracks and click the little calculator thingy it recalculates my calories used value. I don't know if it takes the basic info from the Garmin file and applies a different algorithm but the value is always less than the Garmin value. But I have no idea how that compares to Polar data imported into SportTracks. Does anyone know?

magliaceleste

Sportstracks does it's own calculation from the raw data when you press the calc button.

The calories are still too high. That's comparing to the values obtained from Powermeters (more accurate than anything else) but not by as much as Garmin's crazy numbers.

I'll try and work out the rough %.

freehub

The Garmin calorie counter is designed for big fat Americans.

drewfromrisca

Yeah Will, why just fat americans?