Calories used

[colly]

I recently aquired a Garmin Edge 500 and have been logging my rides this year on two online sites.

One is 'Garmin' the other is 'Ride with GPS'. They give the same information but display it in slightly different ways.

Both accept the information uploaded from the Edge 500 and each gives pretty much the same results with regards to distance, hr, speed, eleveation and so on but when it comes to the calculated calories used they vary massively.

On Sunday I did around 35 miles with about 1600 ft of climbing and the calories Garmin suggest I used is around 900. Ride with GPS however suggests that I will have used something like 2500. I find that hard to believe but they do explain the method and also unlike Garmin they ask for not just my weight but the weight of the bike and me together.

I'm not really wanting to lose weight so I'm not counting calories but I wondered if anyone here could suggest why there is such a difference between the site.

Thanks.

 

[Garz]

I generally would take the garmin figure and multiply it by 0.8 (or 80%). Most electronics way over-estimate calories burned. FWIW I never log my calories, I am more interested in the distance, elevation and HR. If I could be lucky enough to afford a power meter then that would be more beneficial.


The reason they are out is due to the variables involved i.e. height, age , weight, fat %, metabolism, fitness level etc. They may use a different algorithm to get their estimate.

 

[colly]

Thanks Garz.

I think I already had an idea Garmin would be nearer the real figure anyway because that 'seemed' more realistic somehow. 80% of that then would perhaps be even more realistic.

 

[Fiona N]

I think Garz' idea will result in a significant under-tally. After all, if you rode 35 flat miles in two hours, you'd be looking at around 1000 kcal energy expended (@500 kcal / hr), if you were slower, then less, but add in about 500m of climbing and you've added a significant extra element.

The other thing to consider is what the websites are giving you - i.e. is it total energy expended by your body over the time interval (bearing in mind that basal metabolic requirements will be of the order of 100 kcal per hour i.e. 2400 kcal per day for a typical male) so sitting in a cafe for an hour will add to the total or is it just the additional calories due to riding and climbing - which is obviously a significantly smaller number.

 

[Dan B]

I would be very dubious of any calorie expenditure estimate for pretty much any activity of more than about 700-1000 per hour.

Most electronics devices overestimate because it makes their users feel better about themselves.

 

[colly]

Well. Since I posted I have looked at the Ride with GPS site and they say they point to this:

http://www.braydenwm.com/calburn.htm
and to this:
http://www.braydenwm.com/cal_vs_hr_ref_paper.pdf

as their method of calulation.

Checking on the Garmin site and scanning through the forum I see that a common gripe is that the Garmin 500 and others will, in the owners estimation at least, give a calorie count very much on the low side.

Indications on there also suggest that a count of 35 to 40 calories per mile are a good average/reasonable assumption depending on fitness, equipment, speed etc.

I did 35 miles the other day and if those estimates are right then I would have used something like 1225 - 1400 calories. The ride had a fair amount of climbing (1600ft) so perhaps that would be a low estimate.

Confused? Quite possibly, but it seems to me that there is no definitive way of calculation using HR alone so I'll most likely ignore it or at any rate take an average of the two readings I get.

 

[Fiona N]

I've done a sort of rough 'calibration' of energy expended by using the values I get from the turbo trained compared to what the HRM software (Polar) says.

The turbo has a power function (when I trained seriously, I used to have this function calibrated - before the days of Powertap etc.) and can obviously work out from the power you're generating how many calories you've expended to generate that power - independently of individual weight/sex/age etc. - using efficiency (which is estimated for the individual but it's not a hugely variable factor compared to body weight).

This gives a calorie expended total for the exercise while the Polar software generates an exertion factor based on your heart rate (sampled during the exercise every 5s or 15s - in my set-up - not just the average HR, as well as an exercise-dependent variable, as swimming isn't the same as running, for example). I've found that the exertion is about a factor of 4 less than the calories calculated by the turbo and I use this as a rough rule of thumb for cycling. Generally this means that I average a bit over 500kcal/hour on rides around South Lakes as I tend to ride hilly routes slower (recovering on downhill and flats) than flatter routes which I use to try and increase my average speed.

I'm happy that I have a 'rule of thumb' number - not the most precise but it does give me a feel for the work I've done - and I'm an anorak for numbers

 

[Dan B]

Well. Since I posted I have looked at the Ride with GPS site and they say they point to this:

http://www.braydenwm.com/calburn.htm
and to this:
http://www.braydenwm...r_ref_paper.pdf

as their method of calulation.

The same one as everyone else, then. I wonder why their answer is so high?


The paper says

The relationship between

heart rate and energy expenditure is linear only within a relatively narrow range
of approximately 90-150 beats x [min.sup.-1] (the so-called "flex heart rate") during physical activity During light activity or inactivity, there is
almost no slope to the relationship between heart rate and energy expenditure,
and for the purpose of measuring energy expenditure from heart rate it is
assumed that energy expenditure is equal to resting energy expenditure

I suspect that the 90 and 150 limits are averages across a population and in an individual should be adjusted so they actually relate to exertion levels (as it says, light activity expends no more energy than resting), but that the ridewithgps site don't make any such adjustment, and possibly you're getting a significant overestimate on any sections (downhills?) that you're not really exerting yourself much, but in which your heart rate is above the 90 limit. Am I making any sense here? I'm certainly not punctuating very well.

 

[overgeared]

your calorie consumption depends on your fitness (VO2max) and how much of it your use (how hard you go) and for how long. unless your garmin is wired up to a power meter or unless you know exactly your VO2max and can program that into one of these devices, and it's receiving a heart rate feed, then they have little hope of reporting accurately your energy consumption.

the difference between your two numbers 900 and 2400 is massive. maybe one unit is estimating energy spend at the pedals and the other is estimating total energy spend which is typically around 4 times higher (of every 100 calories you burn while cycling only around 25 are converted to mechanical work at the pedals).

have a look here for greater detail.

 

[amaferanga]

Based on my power meter I'd estimate that for a 35 mile hilly ride that takes 2 hours I'd burn about 1400-1600 calories. That'd be an average power of about 220 Watts. If you're a big powerful rider then that would be a very achievable Wattage, but if you're on the small side then even that might be a bit much for you (especially given that for hilly rides you spend a fair bit of time coasting so 220 Watts average would be more like ~270W average excluding zeros).

900 kcal is too low. 2500 is way too high - if you did 35 miles in an hour then maybe you'd burn around 2500 kcal.

 

[colly]

Based on my power meter I'd estimate that for a 35 mile hilly ride that takes 2 hours I'd burn about 1400-1600 calories. That'd be an average power of about 220 Watts. If you're a big powerful rider then that would be a very achievable Wattage, but if you're on the small side then even that might be a bit much for you (especially given that for hilly rides you spend a fair bit of time coasting so 220 Watts average would be more like ~270W average excluding zeros).

900 kcal is too low. 2500 is way too high - if you did 35 miles in an hour then maybe you'd burn around 2500 kcal.

Thanks thats very informative.

The actual stats I got from RWGPS are :

34.9 mi +1,585 ft
02:16:39 Max HR 162
Avg HR 141
Zone 1: 9m8s
Zone 2: 1h6m
Zone 3: 1h11m
Zone 4: 14m36s
Zone 5: 0s
Avg Watts 247
Calories 2848

I'm not a big bloke and seeing as how I am 59, and although I have been cycling regularly and often for years this years efforts are minimal to say the least I would guess that there is no way I could be pushing out 247watts as an average. Especially as you have access to a powermeter and reckon 220 would be about right for an average 17.5mph over two hours.

The actual stats from Garmin are :


Time: 02:18:15
Distance: 34,93 mi
Elevation Gain: 1.564 ft
Calories: 868 C
Avg Temperature: 41,9 °F

The average calorie count from the two sites comes in at 1858 which still seems high to me.

All very confusing.

Maybe I'll contact both sites and ask why they come up with such different results and see what they say. If I get a response from either or both places I'll post them.

Thanks again.